Bug Summary

File:llvm/lib/Transforms/Utils/LoopPeel.cpp
Warning:line 839, column 3
Called C++ object pointer is null

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clang -cc1 -cc1 -triple x86_64-pc-linux-gnu -analyze -disable-free -disable-llvm-verifier -discard-value-names -main-file-name LoopPeel.cpp -analyzer-store=region -analyzer-opt-analyze-nested-blocks -analyzer-checker=core -analyzer-checker=apiModeling -analyzer-checker=unix -analyzer-checker=deadcode -analyzer-checker=cplusplus -analyzer-checker=security.insecureAPI.UncheckedReturn -analyzer-checker=security.insecureAPI.getpw -analyzer-checker=security.insecureAPI.gets -analyzer-checker=security.insecureAPI.mktemp -analyzer-checker=security.insecureAPI.mkstemp -analyzer-checker=security.insecureAPI.vfork -analyzer-checker=nullability.NullPassedToNonnull -analyzer-checker=nullability.NullReturnedFromNonnull -analyzer-output plist -w -setup-static-analyzer -analyzer-config-compatibility-mode=true -mrelocation-model pic -pic-level 2 -fhalf-no-semantic-interposition -mframe-pointer=none -fmath-errno -fno-rounding-math -mconstructor-aliases -munwind-tables -target-cpu x86-64 -tune-cpu generic -fno-split-dwarf-inlining -debugger-tuning=gdb -ffunction-sections -fdata-sections -resource-dir /usr/lib/llvm-12/lib/clang/12.0.0 -D _DEBUG -D _GNU_SOURCE -D __STDC_CONSTANT_MACROS -D __STDC_FORMAT_MACROS -D __STDC_LIMIT_MACROS -I /build/llvm-toolchain-snapshot-12~++20210125100614+2cdb34efdac5/build-llvm/lib/Transforms/Utils -I /build/llvm-toolchain-snapshot-12~++20210125100614+2cdb34efdac5/llvm/lib/Transforms/Utils -I /build/llvm-toolchain-snapshot-12~++20210125100614+2cdb34efdac5/build-llvm/include -I /build/llvm-toolchain-snapshot-12~++20210125100614+2cdb34efdac5/llvm/include -U NDEBUG -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/6.3.0/../../../../include/c++/6.3.0 -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/6.3.0/../../../../include/x86_64-linux-gnu/c++/6.3.0 -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/6.3.0/../../../../include/x86_64-linux-gnu/c++/6.3.0 -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/6.3.0/../../../../include/c++/6.3.0/backward -internal-isystem /usr/local/include -internal-isystem /usr/lib/llvm-12/lib/clang/12.0.0/include -internal-externc-isystem /usr/include/x86_64-linux-gnu -internal-externc-isystem /include -internal-externc-isystem /usr/include -O2 -Wno-unused-parameter -Wwrite-strings -Wno-missing-field-initializers -Wno-long-long -Wno-maybe-uninitialized -Wno-comment -std=c++14 -fdeprecated-macro -fdebug-compilation-dir /build/llvm-toolchain-snapshot-12~++20210125100614+2cdb34efdac5/build-llvm/lib/Transforms/Utils -fdebug-prefix-map=/build/llvm-toolchain-snapshot-12~++20210125100614+2cdb34efdac5=. -ferror-limit 19 -fvisibility-inlines-hidden -stack-protector 2 -fgnuc-version=4.2.1 -vectorize-loops -vectorize-slp -analyzer-output=html -analyzer-config stable-report-filename=true -faddrsig -o /tmp/scan-build-2021-01-26-035717-31997-1 -x c++ /build/llvm-toolchain-snapshot-12~++20210125100614+2cdb34efdac5/llvm/lib/Transforms/Utils/LoopPeel.cpp
1//===- LoopPeel.cpp -------------------------------------------------------===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8//
9// Loop Peeling Utilities.
10//===----------------------------------------------------------------------===//
11
12#include "llvm/Transforms/Utils/LoopPeel.h"
13#include "llvm/ADT/DenseMap.h"
14#include "llvm/ADT/Optional.h"
15#include "llvm/ADT/SmallVector.h"
16#include "llvm/ADT/Statistic.h"
17#include "llvm/Analysis/LoopInfo.h"
18#include "llvm/Analysis/LoopIterator.h"
19#include "llvm/Analysis/ScalarEvolution.h"
20#include "llvm/Analysis/ScalarEvolutionExpressions.h"
21#include "llvm/Analysis/TargetTransformInfo.h"
22#include "llvm/IR/BasicBlock.h"
23#include "llvm/IR/Dominators.h"
24#include "llvm/IR/Function.h"
25#include "llvm/IR/InstrTypes.h"
26#include "llvm/IR/Instruction.h"
27#include "llvm/IR/Instructions.h"
28#include "llvm/IR/LLVMContext.h"
29#include "llvm/IR/MDBuilder.h"
30#include "llvm/IR/Metadata.h"
31#include "llvm/IR/PatternMatch.h"
32#include "llvm/Support/Casting.h"
33#include "llvm/Support/CommandLine.h"
34#include "llvm/Support/Debug.h"
35#include "llvm/Support/raw_ostream.h"
36#include "llvm/Transforms/Utils/BasicBlockUtils.h"
37#include "llvm/Transforms/Utils/Cloning.h"
38#include "llvm/Transforms/Utils/LoopSimplify.h"
39#include "llvm/Transforms/Utils/LoopUtils.h"
40#include "llvm/Transforms/Utils/UnrollLoop.h"
41#include "llvm/Transforms/Utils/ValueMapper.h"
42#include <algorithm>
43#include <cassert>
44#include <cstdint>
45#include <limits>
46
47using namespace llvm;
48using namespace llvm::PatternMatch;
49
50#define DEBUG_TYPE"loop-peel" "loop-peel"
51
52STATISTIC(NumPeeled, "Number of loops peeled")static llvm::Statistic NumPeeled = {"loop-peel", "NumPeeled",
"Number of loops peeled"};
53
54static cl::opt<unsigned> UnrollPeelCount(
55 "unroll-peel-count", cl::Hidden,
56 cl::desc("Set the unroll peeling count, for testing purposes"));
57
58static cl::opt<bool>
59 UnrollAllowPeeling("unroll-allow-peeling", cl::init(true), cl::Hidden,
60 cl::desc("Allows loops to be peeled when the dynamic "
61 "trip count is known to be low."));
62
63static cl::opt<bool>
64 UnrollAllowLoopNestsPeeling("unroll-allow-loop-nests-peeling",
65 cl::init(false), cl::Hidden,
66 cl::desc("Allows loop nests to be peeled."));
67
68static cl::opt<unsigned> UnrollPeelMaxCount(
69 "unroll-peel-max-count", cl::init(7), cl::Hidden,
70 cl::desc("Max average trip count which will cause loop peeling."));
71
72static cl::opt<unsigned> UnrollForcePeelCount(
73 "unroll-force-peel-count", cl::init(0), cl::Hidden,
74 cl::desc("Force a peel count regardless of profiling information."));
75
76static cl::opt<bool> UnrollPeelMultiDeoptExit(
77 "unroll-peel-multi-deopt-exit", cl::init(true), cl::Hidden,
78 cl::desc("Allow peeling of loops with multiple deopt exits."));
79
80static const char *PeeledCountMetaData = "llvm.loop.peeled.count";
81
82// Designates that a Phi is estimated to become invariant after an "infinite"
83// number of loop iterations (i.e. only may become an invariant if the loop is
84// fully unrolled).
85static const unsigned InfiniteIterationsToInvariance =
86 std::numeric_limits<unsigned>::max();
87
88// Check whether we are capable of peeling this loop.
89bool llvm::canPeel(Loop *L) {
90 // Make sure the loop is in simplified form
91 if (!L->isLoopSimplifyForm())
92 return false;
93
94 if (UnrollPeelMultiDeoptExit) {
95 SmallVector<BasicBlock *, 4> Exits;
96 L->getUniqueNonLatchExitBlocks(Exits);
97
98 if (!Exits.empty()) {
99 // Latch's terminator is a conditional branch, Latch is exiting and
100 // all non Latch exits ends up with deoptimize.
101 const BasicBlock *Latch = L->getLoopLatch();
102 const BranchInst *T = dyn_cast<BranchInst>(Latch->getTerminator());
103 return T && T->isConditional() && L->isLoopExiting(Latch) &&
104 all_of(Exits, [](const BasicBlock *BB) {
105 return BB->getTerminatingDeoptimizeCall();
106 });
107 }
108 }
109
110 // Only peel loops that contain a single exit
111 if (!L->getExitingBlock() || !L->getUniqueExitBlock())
112 return false;
113
114 // Don't try to peel loops where the latch is not the exiting block.
115 // This can be an indication of two different things:
116 // 1) The loop is not rotated.
117 // 2) The loop contains irreducible control flow that involves the latch.
118 const BasicBlock *Latch = L->getLoopLatch();
119 if (Latch != L->getExitingBlock())
120 return false;
121
122 // Peeling is only supported if the latch is a branch.
123 if (!isa<BranchInst>(Latch->getTerminator()))
124 return false;
125
126 return true;
127}
128
129// This function calculates the number of iterations after which the given Phi
130// becomes an invariant. The pre-calculated values are memorized in the map. The
131// function (shortcut is I) is calculated according to the following definition:
132// Given %x = phi <Inputs from above the loop>, ..., [%y, %back.edge].
133// If %y is a loop invariant, then I(%x) = 1.
134// If %y is a Phi from the loop header, I(%x) = I(%y) + 1.
135// Otherwise, I(%x) is infinite.
136// TODO: Actually if %y is an expression that depends only on Phi %z and some
137// loop invariants, we can estimate I(%x) = I(%z) + 1. The example
138// looks like:
139// %x = phi(0, %a), <-- becomes invariant starting from 3rd iteration.
140// %y = phi(0, 5),
141// %a = %y + 1.
142static unsigned calculateIterationsToInvariance(
143 PHINode *Phi, Loop *L, BasicBlock *BackEdge,
144 SmallDenseMap<PHINode *, unsigned> &IterationsToInvariance) {
145 assert(Phi->getParent() == L->getHeader() &&((Phi->getParent() == L->getHeader() && "Non-loop Phi should not be checked for turning into invariant."
) ? static_cast<void> (0) : __assert_fail ("Phi->getParent() == L->getHeader() && \"Non-loop Phi should not be checked for turning into invariant.\""
, "/build/llvm-toolchain-snapshot-12~++20210125100614+2cdb34efdac5/llvm/lib/Transforms/Utils/LoopPeel.cpp"
, 146, __PRETTY_FUNCTION__))
146 "Non-loop Phi should not be checked for turning into invariant.")((Phi->getParent() == L->getHeader() && "Non-loop Phi should not be checked for turning into invariant."
) ? static_cast<void> (0) : __assert_fail ("Phi->getParent() == L->getHeader() && \"Non-loop Phi should not be checked for turning into invariant.\""
, "/build/llvm-toolchain-snapshot-12~++20210125100614+2cdb34efdac5/llvm/lib/Transforms/Utils/LoopPeel.cpp"
, 146, __PRETTY_FUNCTION__));
147 assert(BackEdge == L->getLoopLatch() && "Wrong latch?")((BackEdge == L->getLoopLatch() && "Wrong latch?")
? static_cast<void> (0) : __assert_fail ("BackEdge == L->getLoopLatch() && \"Wrong latch?\""
, "/build/llvm-toolchain-snapshot-12~++20210125100614+2cdb34efdac5/llvm/lib/Transforms/Utils/LoopPeel.cpp"
, 147, __PRETTY_FUNCTION__));
148 // If we already know the answer, take it from the map.
149 auto I = IterationsToInvariance.find(Phi);
150 if (I != IterationsToInvariance.end())
151 return I->second;
152
153 // Otherwise we need to analyze the input from the back edge.
154 Value *Input = Phi->getIncomingValueForBlock(BackEdge);
155 // Place infinity to map to avoid infinite recursion for cycled Phis. Such
156 // cycles can never stop on an invariant.
157 IterationsToInvariance[Phi] = InfiniteIterationsToInvariance;
158 unsigned ToInvariance = InfiniteIterationsToInvariance;
159
160 if (L->isLoopInvariant(Input))
161 ToInvariance = 1u;
162 else if (PHINode *IncPhi = dyn_cast<PHINode>(Input)) {
163 // Only consider Phis in header block.
164 if (IncPhi->getParent() != L->getHeader())
165 return InfiniteIterationsToInvariance;
166 // If the input becomes an invariant after X iterations, then our Phi
167 // becomes an invariant after X + 1 iterations.
168 unsigned InputToInvariance = calculateIterationsToInvariance(
169 IncPhi, L, BackEdge, IterationsToInvariance);
170 if (InputToInvariance != InfiniteIterationsToInvariance)
171 ToInvariance = InputToInvariance + 1u;
172 }
173
174 // If we found that this Phi lies in an invariant chain, update the map.
175 if (ToInvariance != InfiniteIterationsToInvariance)
176 IterationsToInvariance[Phi] = ToInvariance;
177 return ToInvariance;
178}
179
180// Return the number of iterations to peel off that make conditions in the
181// body true/false. For example, if we peel 2 iterations off the loop below,
182// the condition i < 2 can be evaluated at compile time.
183// for (i = 0; i < n; i++)
184// if (i < 2)
185// ..
186// else
187// ..
188// }
189static unsigned countToEliminateCompares(Loop &L, unsigned MaxPeelCount,
190 ScalarEvolution &SE) {
191 assert(L.isLoopSimplifyForm() && "Loop needs to be in loop simplify form")((L.isLoopSimplifyForm() && "Loop needs to be in loop simplify form"
) ? static_cast<void> (0) : __assert_fail ("L.isLoopSimplifyForm() && \"Loop needs to be in loop simplify form\""
, "/build/llvm-toolchain-snapshot-12~++20210125100614+2cdb34efdac5/llvm/lib/Transforms/Utils/LoopPeel.cpp"
, 191, __PRETTY_FUNCTION__));
192 unsigned DesiredPeelCount = 0;
193
194 for (auto *BB : L.blocks()) {
195 auto *BI = dyn_cast<BranchInst>(BB->getTerminator());
196 if (!BI || BI->isUnconditional())
197 continue;
198
199 // Ignore loop exit condition.
200 if (L.getLoopLatch() == BB)
201 continue;
202
203 Value *Condition = BI->getCondition();
204 Value *LeftVal, *RightVal;
205 CmpInst::Predicate Pred;
206 if (!match(Condition, m_ICmp(Pred, m_Value(LeftVal), m_Value(RightVal))))
207 continue;
208
209 const SCEV *LeftSCEV = SE.getSCEV(LeftVal);
210 const SCEV *RightSCEV = SE.getSCEV(RightVal);
211
212 // Do not consider predicates that are known to be true or false
213 // independently of the loop iteration.
214 if (SE.isKnownPredicate(Pred, LeftSCEV, RightSCEV) ||
215 SE.isKnownPredicate(ICmpInst::getInversePredicate(Pred), LeftSCEV,
216 RightSCEV))
217 continue;
218
219 // Check if we have a condition with one AddRec and one non AddRec
220 // expression. Normalize LeftSCEV to be the AddRec.
221 if (!isa<SCEVAddRecExpr>(LeftSCEV)) {
222 if (isa<SCEVAddRecExpr>(RightSCEV)) {
223 std::swap(LeftSCEV, RightSCEV);
224 Pred = ICmpInst::getSwappedPredicate(Pred);
225 } else
226 continue;
227 }
228
229 const SCEVAddRecExpr *LeftAR = cast<SCEVAddRecExpr>(LeftSCEV);
230
231 // Avoid huge SCEV computations in the loop below, make sure we only
232 // consider AddRecs of the loop we are trying to peel.
233 if (!LeftAR->isAffine() || LeftAR->getLoop() != &L)
234 continue;
235 if (!(ICmpInst::isEquality(Pred) && LeftAR->hasNoSelfWrap()) &&
236 !SE.getMonotonicPredicateType(LeftAR, Pred))
237 continue;
238
239 // Check if extending the current DesiredPeelCount lets us evaluate Pred
240 // or !Pred in the loop body statically.
241 unsigned NewPeelCount = DesiredPeelCount;
242
243 const SCEV *IterVal = LeftAR->evaluateAtIteration(
244 SE.getConstant(LeftSCEV->getType(), NewPeelCount), SE);
245
246 // If the original condition is not known, get the negated predicate
247 // (which holds on the else branch) and check if it is known. This allows
248 // us to peel of iterations that make the original condition false.
249 if (!SE.isKnownPredicate(Pred, IterVal, RightSCEV))
250 Pred = ICmpInst::getInversePredicate(Pred);
251
252 const SCEV *Step = LeftAR->getStepRecurrence(SE);
253 const SCEV *NextIterVal = SE.getAddExpr(IterVal, Step);
254 auto PeelOneMoreIteration = [&IterVal, &NextIterVal, &SE, Step,
255 &NewPeelCount]() {
256 IterVal = NextIterVal;
257 NextIterVal = SE.getAddExpr(IterVal, Step);
258 NewPeelCount++;
259 };
260
261 auto CanPeelOneMoreIteration = [&NewPeelCount, &MaxPeelCount]() {
262 return NewPeelCount < MaxPeelCount;
263 };
264
265 while (CanPeelOneMoreIteration() &&
266 SE.isKnownPredicate(Pred, IterVal, RightSCEV))
267 PeelOneMoreIteration();
268
269 // With *that* peel count, does the predicate !Pred become known in the
270 // first iteration of the loop body after peeling?
271 if (!SE.isKnownPredicate(ICmpInst::getInversePredicate(Pred), IterVal,
272 RightSCEV))
273 continue; // If not, give up.
274
275 // However, for equality comparisons, that isn't always sufficient to
276 // eliminate the comparsion in loop body, we may need to peel one more
277 // iteration. See if that makes !Pred become unknown again.
278 if (ICmpInst::isEquality(Pred) &&
279 !SE.isKnownPredicate(ICmpInst::getInversePredicate(Pred), NextIterVal,
280 RightSCEV) &&
281 !SE.isKnownPredicate(Pred, IterVal, RightSCEV) &&
282 SE.isKnownPredicate(Pred, NextIterVal, RightSCEV)) {
283 if (!CanPeelOneMoreIteration())
284 continue; // Need to peel one more iteration, but can't. Give up.
285 PeelOneMoreIteration(); // Great!
286 }
287
288 DesiredPeelCount = std::max(DesiredPeelCount, NewPeelCount);
289 }
290
291 return DesiredPeelCount;
292}
293
294// Return the number of iterations we want to peel off.
295void llvm::computePeelCount(Loop *L, unsigned LoopSize,
296 TargetTransformInfo::PeelingPreferences &PP,
297 unsigned &TripCount, ScalarEvolution &SE,
298 unsigned Threshold) {
299 assert(LoopSize > 0 && "Zero loop size is not allowed!")((LoopSize > 0 && "Zero loop size is not allowed!"
) ? static_cast<void> (0) : __assert_fail ("LoopSize > 0 && \"Zero loop size is not allowed!\""
, "/build/llvm-toolchain-snapshot-12~++20210125100614+2cdb34efdac5/llvm/lib/Transforms/Utils/LoopPeel.cpp"
, 299, __PRETTY_FUNCTION__));
300 // Save the PP.PeelCount value set by the target in
301 // TTI.getPeelingPreferences or by the flag -unroll-peel-count.
302 unsigned TargetPeelCount = PP.PeelCount;
303 PP.PeelCount = 0;
304 if (!canPeel(L))
305 return;
306
307 // Only try to peel innermost loops by default.
308 // The constraint can be relaxed by the target in TTI.getUnrollingPreferences
309 // or by the flag -unroll-allow-loop-nests-peeling.
310 if (!PP.AllowLoopNestsPeeling && !L->isInnermost())
311 return;
312
313 // If the user provided a peel count, use that.
314 bool UserPeelCount = UnrollForcePeelCount.getNumOccurrences() > 0;
315 if (UserPeelCount) {
316 LLVM_DEBUG(dbgs() << "Force-peeling first " << UnrollForcePeelCountdo { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-peel")) { dbgs() << "Force-peeling first " <<
UnrollForcePeelCount << " iterations.\n"; } } while (false
)
317 << " iterations.\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-peel")) { dbgs() << "Force-peeling first " <<
UnrollForcePeelCount << " iterations.\n"; } } while (false
);
318 PP.PeelCount = UnrollForcePeelCount;
319 PP.PeelProfiledIterations = true;
320 return;
321 }
322
323 // Skip peeling if it's disabled.
324 if (!PP.AllowPeeling)
325 return;
326
327 unsigned AlreadyPeeled = 0;
328 if (auto Peeled = getOptionalIntLoopAttribute(L, PeeledCountMetaData))
329 AlreadyPeeled = *Peeled;
330 // Stop if we already peeled off the maximum number of iterations.
331 if (AlreadyPeeled >= UnrollPeelMaxCount)
332 return;
333
334 // Here we try to get rid of Phis which become invariants after 1, 2, ..., N
335 // iterations of the loop. For this we compute the number for iterations after
336 // which every Phi is guaranteed to become an invariant, and try to peel the
337 // maximum number of iterations among these values, thus turning all those
338 // Phis into invariants.
339 // First, check that we can peel at least one iteration.
340 if (2 * LoopSize <= Threshold && UnrollPeelMaxCount > 0) {
341 // Store the pre-calculated values here.
342 SmallDenseMap<PHINode *, unsigned> IterationsToInvariance;
343 // Now go through all Phis to calculate their the number of iterations they
344 // need to become invariants.
345 // Start the max computation with the UP.PeelCount value set by the target
346 // in TTI.getUnrollingPreferences or by the flag -unroll-peel-count.
347 unsigned DesiredPeelCount = TargetPeelCount;
348 BasicBlock *BackEdge = L->getLoopLatch();
349 assert(BackEdge && "Loop is not in simplified form?")((BackEdge && "Loop is not in simplified form?") ? static_cast
<void> (0) : __assert_fail ("BackEdge && \"Loop is not in simplified form?\""
, "/build/llvm-toolchain-snapshot-12~++20210125100614+2cdb34efdac5/llvm/lib/Transforms/Utils/LoopPeel.cpp"
, 349, __PRETTY_FUNCTION__));
350 for (auto BI = L->getHeader()->begin(); isa<PHINode>(&*BI); ++BI) {
351 PHINode *Phi = cast<PHINode>(&*BI);
352 unsigned ToInvariance = calculateIterationsToInvariance(
353 Phi, L, BackEdge, IterationsToInvariance);
354 if (ToInvariance != InfiniteIterationsToInvariance)
355 DesiredPeelCount = std::max(DesiredPeelCount, ToInvariance);
356 }
357
358 // Pay respect to limitations implied by loop size and the max peel count.
359 unsigned MaxPeelCount = UnrollPeelMaxCount;
360 MaxPeelCount = std::min(MaxPeelCount, Threshold / LoopSize - 1);
361
362 DesiredPeelCount = std::max(DesiredPeelCount,
363 countToEliminateCompares(*L, MaxPeelCount, SE));
364
365 if (DesiredPeelCount > 0) {
366 DesiredPeelCount = std::min(DesiredPeelCount, MaxPeelCount);
367 // Consider max peel count limitation.
368 assert(DesiredPeelCount > 0 && "Wrong loop size estimation?")((DesiredPeelCount > 0 && "Wrong loop size estimation?"
) ? static_cast<void> (0) : __assert_fail ("DesiredPeelCount > 0 && \"Wrong loop size estimation?\""
, "/build/llvm-toolchain-snapshot-12~++20210125100614+2cdb34efdac5/llvm/lib/Transforms/Utils/LoopPeel.cpp"
, 368, __PRETTY_FUNCTION__));
369 if (DesiredPeelCount + AlreadyPeeled <= UnrollPeelMaxCount) {
370 LLVM_DEBUG(dbgs() << "Peel " << DesiredPeelCountdo { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-peel")) { dbgs() << "Peel " << DesiredPeelCount
<< " iteration(s) to turn" << " some Phis into invariants.\n"
; } } while (false)
371 << " iteration(s) to turn"do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-peel")) { dbgs() << "Peel " << DesiredPeelCount
<< " iteration(s) to turn" << " some Phis into invariants.\n"
; } } while (false)
372 << " some Phis into invariants.\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-peel")) { dbgs() << "Peel " << DesiredPeelCount
<< " iteration(s) to turn" << " some Phis into invariants.\n"
; } } while (false);
373 PP.PeelCount = DesiredPeelCount;
374 PP.PeelProfiledIterations = false;
375 return;
376 }
377 }
378 }
379
380 // Bail if we know the statically calculated trip count.
381 // In this case we rather prefer partial unrolling.
382 if (TripCount)
383 return;
384
385 // Do not apply profile base peeling if it is disabled.
386 if (!PP.PeelProfiledIterations)
387 return;
388 // If we don't know the trip count, but have reason to believe the average
389 // trip count is low, peeling should be beneficial, since we will usually
390 // hit the peeled section.
391 // We only do this in the presence of profile information, since otherwise
392 // our estimates of the trip count are not reliable enough.
393 if (L->getHeader()->getParent()->hasProfileData()) {
394 Optional<unsigned> PeelCount = getLoopEstimatedTripCount(L);
395 if (!PeelCount)
396 return;
397
398 LLVM_DEBUG(dbgs() << "Profile-based estimated trip count is " << *PeelCountdo { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-peel")) { dbgs() << "Profile-based estimated trip count is "
<< *PeelCount << "\n"; } } while (false)
399 << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-peel")) { dbgs() << "Profile-based estimated trip count is "
<< *PeelCount << "\n"; } } while (false);
400
401 if (*PeelCount) {
402 if ((*PeelCount + AlreadyPeeled <= UnrollPeelMaxCount) &&
403 (LoopSize * (*PeelCount + 1) <= Threshold)) {
404 LLVM_DEBUG(dbgs() << "Peeling first " << *PeelCountdo { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-peel")) { dbgs() << "Peeling first " << *PeelCount
<< " iterations.\n"; } } while (false)
405 << " iterations.\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-peel")) { dbgs() << "Peeling first " << *PeelCount
<< " iterations.\n"; } } while (false);
406 PP.PeelCount = *PeelCount;
407 return;
408 }
409 LLVM_DEBUG(dbgs() << "Requested peel count: " << *PeelCount << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-peel")) { dbgs() << "Requested peel count: " <<
*PeelCount << "\n"; } } while (false);
410 LLVM_DEBUG(dbgs() << "Already peel count: " << AlreadyPeeled << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-peel")) { dbgs() << "Already peel count: " <<
AlreadyPeeled << "\n"; } } while (false);
411 LLVM_DEBUG(dbgs() << "Max peel count: " << UnrollPeelMaxCount << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-peel")) { dbgs() << "Max peel count: " << UnrollPeelMaxCount
<< "\n"; } } while (false);
412 LLVM_DEBUG(dbgs() << "Peel cost: " << LoopSize * (*PeelCount + 1)do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-peel")) { dbgs() << "Peel cost: " << LoopSize
* (*PeelCount + 1) << "\n"; } } while (false)
413 << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-peel")) { dbgs() << "Peel cost: " << LoopSize
* (*PeelCount + 1) << "\n"; } } while (false);
414 LLVM_DEBUG(dbgs() << "Max peel cost: " << Threshold << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-peel")) { dbgs() << "Max peel cost: " << Threshold
<< "\n"; } } while (false);
415 }
416 }
417}
418
419/// Update the branch weights of the latch of a peeled-off loop
420/// iteration.
421/// This sets the branch weights for the latch of the recently peeled off loop
422/// iteration correctly.
423/// Let F is a weight of the edge from latch to header.
424/// Let E is a weight of the edge from latch to exit.
425/// F/(F+E) is a probability to go to loop and E/(F+E) is a probability to
426/// go to exit.
427/// Then, Estimated TripCount = F / E.
428/// For I-th (counting from 0) peeled off iteration we set the the weights for
429/// the peeled latch as (TC - I, 1). It gives us reasonable distribution,
430/// The probability to go to exit 1/(TC-I) increases. At the same time
431/// the estimated trip count of remaining loop reduces by I.
432/// To avoid dealing with division rounding we can just multiple both part
433/// of weights to E and use weight as (F - I * E, E).
434///
435/// \param Header The copy of the header block that belongs to next iteration.
436/// \param LatchBR The copy of the latch branch that belongs to this iteration.
437/// \param[in,out] FallThroughWeight The weight of the edge from latch to
438/// header before peeling (in) and after peeled off one iteration (out).
439static void updateBranchWeights(BasicBlock *Header, BranchInst *LatchBR,
440 uint64_t ExitWeight,
441 uint64_t &FallThroughWeight) {
442 // FallThroughWeight is 0 means that there is no branch weights on original
443 // latch block or estimated trip count is zero.
444 if (!FallThroughWeight)
445 return;
446
447 unsigned HeaderIdx = (LatchBR->getSuccessor(0) == Header ? 0 : 1);
448 MDBuilder MDB(LatchBR->getContext());
449 MDNode *WeightNode =
450 HeaderIdx ? MDB.createBranchWeights(ExitWeight, FallThroughWeight)
451 : MDB.createBranchWeights(FallThroughWeight, ExitWeight);
452 LatchBR->setMetadata(LLVMContext::MD_prof, WeightNode);
453 FallThroughWeight =
454 FallThroughWeight > ExitWeight ? FallThroughWeight - ExitWeight : 1;
455}
456
457/// Initialize the weights.
458///
459/// \param Header The header block.
460/// \param LatchBR The latch branch.
461/// \param[out] ExitWeight The weight of the edge from Latch to Exit.
462/// \param[out] FallThroughWeight The weight of the edge from Latch to Header.
463static void initBranchWeights(BasicBlock *Header, BranchInst *LatchBR,
464 uint64_t &ExitWeight,
465 uint64_t &FallThroughWeight) {
466 uint64_t TrueWeight, FalseWeight;
467 if (!LatchBR->extractProfMetadata(TrueWeight, FalseWeight))
468 return;
469 unsigned HeaderIdx = LatchBR->getSuccessor(0) == Header ? 0 : 1;
470 ExitWeight = HeaderIdx ? TrueWeight : FalseWeight;
471 FallThroughWeight = HeaderIdx ? FalseWeight : TrueWeight;
472}
473
474/// Update the weights of original Latch block after peeling off all iterations.
475///
476/// \param Header The header block.
477/// \param LatchBR The latch branch.
478/// \param ExitWeight The weight of the edge from Latch to Exit.
479/// \param FallThroughWeight The weight of the edge from Latch to Header.
480static void fixupBranchWeights(BasicBlock *Header, BranchInst *LatchBR,
481 uint64_t ExitWeight,
482 uint64_t FallThroughWeight) {
483 // FallThroughWeight is 0 means that there is no branch weights on original
484 // latch block or estimated trip count is zero.
485 if (!FallThroughWeight)
486 return;
487
488 // Sets the branch weights on the loop exit.
489 MDBuilder MDB(LatchBR->getContext());
490 unsigned HeaderIdx = LatchBR->getSuccessor(0) == Header ? 0 : 1;
491 MDNode *WeightNode =
492 HeaderIdx ? MDB.createBranchWeights(ExitWeight, FallThroughWeight)
493 : MDB.createBranchWeights(FallThroughWeight, ExitWeight);
494 LatchBR->setMetadata(LLVMContext::MD_prof, WeightNode);
495}
496
497/// Clones the body of the loop L, putting it between \p InsertTop and \p
498/// InsertBot.
499/// \param IterNumber The serial number of the iteration currently being
500/// peeled off.
501/// \param ExitEdges The exit edges of the original loop.
502/// \param[out] NewBlocks A list of the blocks in the newly created clone
503/// \param[out] VMap The value map between the loop and the new clone.
504/// \param LoopBlocks A helper for DFS-traversal of the loop.
505/// \param LVMap A value-map that maps instructions from the original loop to
506/// instructions in the last peeled-off iteration.
507static void cloneLoopBlocks(
508 Loop *L, unsigned IterNumber, BasicBlock *InsertTop, BasicBlock *InsertBot,
509 SmallVectorImpl<std::pair<BasicBlock *, BasicBlock *>> &ExitEdges,
510 SmallVectorImpl<BasicBlock *> &NewBlocks, LoopBlocksDFS &LoopBlocks,
511 ValueToValueMapTy &VMap, ValueToValueMapTy &LVMap, DominatorTree *DT,
512 LoopInfo *LI) {
513 BasicBlock *Header = L->getHeader();
514 BasicBlock *Latch = L->getLoopLatch();
515 BasicBlock *PreHeader = L->getLoopPreheader();
516
517 Function *F = Header->getParent();
518 LoopBlocksDFS::RPOIterator BlockBegin = LoopBlocks.beginRPO();
519 LoopBlocksDFS::RPOIterator BlockEnd = LoopBlocks.endRPO();
520 Loop *ParentLoop = L->getParentLoop();
521
522 // For each block in the original loop, create a new copy,
523 // and update the value map with the newly created values.
524 for (LoopBlocksDFS::RPOIterator BB = BlockBegin; BB != BlockEnd; ++BB) {
525 BasicBlock *NewBB = CloneBasicBlock(*BB, VMap, ".peel", F);
526 NewBlocks.push_back(NewBB);
527
528 // If an original block is an immediate child of the loop L, its copy
529 // is a child of a ParentLoop after peeling. If a block is a child of
530 // a nested loop, it is handled in the cloneLoop() call below.
531 if (ParentLoop && LI->getLoopFor(*BB) == L)
532 ParentLoop->addBasicBlockToLoop(NewBB, *LI);
533
534 VMap[*BB] = NewBB;
535
536 // If dominator tree is available, insert nodes to represent cloned blocks.
537 if (DT) {
538 if (Header == *BB)
539 DT->addNewBlock(NewBB, InsertTop);
540 else {
541 DomTreeNode *IDom = DT->getNode(*BB)->getIDom();
542 // VMap must contain entry for IDom, as the iteration order is RPO.
543 DT->addNewBlock(NewBB, cast<BasicBlock>(VMap[IDom->getBlock()]));
544 }
545 }
546 }
547
548 // Recursively create the new Loop objects for nested loops, if any,
549 // to preserve LoopInfo.
550 for (Loop *ChildLoop : *L) {
551 cloneLoop(ChildLoop, ParentLoop, VMap, LI, nullptr);
552 }
553
554 // Hook-up the control flow for the newly inserted blocks.
555 // The new header is hooked up directly to the "top", which is either
556 // the original loop preheader (for the first iteration) or the previous
557 // iteration's exiting block (for every other iteration)
558 InsertTop->getTerminator()->setSuccessor(0, cast<BasicBlock>(VMap[Header]));
559
560 // Similarly, for the latch:
561 // The original exiting edge is still hooked up to the loop exit.
562 // The backedge now goes to the "bottom", which is either the loop's real
563 // header (for the last peeled iteration) or the copied header of the next
564 // iteration (for every other iteration)
565 BasicBlock *NewLatch = cast<BasicBlock>(VMap[Latch]);
566 BranchInst *LatchBR = cast<BranchInst>(NewLatch->getTerminator());
567 for (unsigned idx = 0, e = LatchBR->getNumSuccessors(); idx < e; ++idx)
568 if (LatchBR->getSuccessor(idx) == Header) {
569 LatchBR->setSuccessor(idx, InsertBot);
570 break;
571 }
572 if (DT)
573 DT->changeImmediateDominator(InsertBot, NewLatch);
574
575 // The new copy of the loop body starts with a bunch of PHI nodes
576 // that pick an incoming value from either the preheader, or the previous
577 // loop iteration. Since this copy is no longer part of the loop, we
578 // resolve this statically:
579 // For the first iteration, we use the value from the preheader directly.
580 // For any other iteration, we replace the phi with the value generated by
581 // the immediately preceding clone of the loop body (which represents
582 // the previous iteration).
583 for (BasicBlock::iterator I = Header->begin(); isa<PHINode>(I); ++I) {
584 PHINode *NewPHI = cast<PHINode>(VMap[&*I]);
585 if (IterNumber == 0) {
586 VMap[&*I] = NewPHI->getIncomingValueForBlock(PreHeader);
587 } else {
588 Value *LatchVal = NewPHI->getIncomingValueForBlock(Latch);
589 Instruction *LatchInst = dyn_cast<Instruction>(LatchVal);
590 if (LatchInst && L->contains(LatchInst))
591 VMap[&*I] = LVMap[LatchInst];
592 else
593 VMap[&*I] = LatchVal;
594 }
595 cast<BasicBlock>(VMap[Header])->getInstList().erase(NewPHI);
596 }
597
598 // Fix up the outgoing values - we need to add a value for the iteration
599 // we've just created. Note that this must happen *after* the incoming
600 // values are adjusted, since the value going out of the latch may also be
601 // a value coming into the header.
602 for (auto Edge : ExitEdges)
603 for (PHINode &PHI : Edge.second->phis()) {
604 Value *LatchVal = PHI.getIncomingValueForBlock(Edge.first);
605 Instruction *LatchInst = dyn_cast<Instruction>(LatchVal);
606 if (LatchInst && L->contains(LatchInst))
607 LatchVal = VMap[LatchVal];
608 PHI.addIncoming(LatchVal, cast<BasicBlock>(VMap[Edge.first]));
609 }
610
611 // LastValueMap is updated with the values for the current loop
612 // which are used the next time this function is called.
613 for (auto KV : VMap)
614 LVMap[KV.first] = KV.second;
615}
616
617TargetTransformInfo::PeelingPreferences llvm::gatherPeelingPreferences(
618 Loop *L, ScalarEvolution &SE, const TargetTransformInfo &TTI,
619 Optional<bool> UserAllowPeeling,
620 Optional<bool> UserAllowProfileBasedPeeling, bool UnrollingSpecficValues) {
621 TargetTransformInfo::PeelingPreferences PP;
622
623 // Set the default values.
624 PP.PeelCount = 0;
625 PP.AllowPeeling = true;
626 PP.AllowLoopNestsPeeling = false;
627 PP.PeelProfiledIterations = true;
628
629 // Get the target specifc values.
630 TTI.getPeelingPreferences(L, SE, PP);
631
632 // User specified values using cl::opt.
633 if (UnrollingSpecficValues) {
634 if (UnrollPeelCount.getNumOccurrences() > 0)
635 PP.PeelCount = UnrollPeelCount;
636 if (UnrollAllowPeeling.getNumOccurrences() > 0)
637 PP.AllowPeeling = UnrollAllowPeeling;
638 if (UnrollAllowLoopNestsPeeling.getNumOccurrences() > 0)
639 PP.AllowLoopNestsPeeling = UnrollAllowLoopNestsPeeling;
640 }
641
642 // User specifed values provided by argument.
643 if (UserAllowPeeling.hasValue())
644 PP.AllowPeeling = *UserAllowPeeling;
645 if (UserAllowProfileBasedPeeling.hasValue())
646 PP.PeelProfiledIterations = *UserAllowProfileBasedPeeling;
647
648 return PP;
649}
650
651/// Peel off the first \p PeelCount iterations of loop \p L.
652///
653/// Note that this does not peel them off as a single straight-line block.
654/// Rather, each iteration is peeled off separately, and needs to check the
655/// exit condition.
656/// For loops that dynamically execute \p PeelCount iterations or less
657/// this provides a benefit, since the peeled off iterations, which account
658/// for the bulk of dynamic execution, can be further simplified by scalar
659/// optimizations.
660bool llvm::peelLoop(Loop *L, unsigned PeelCount, LoopInfo *LI,
661 ScalarEvolution *SE, DominatorTree *DT, AssumptionCache *AC,
662 bool PreserveLCSSA) {
663 assert(PeelCount > 0 && "Attempt to peel out zero iterations?")((PeelCount > 0 && "Attempt to peel out zero iterations?"
) ? static_cast<void> (0) : __assert_fail ("PeelCount > 0 && \"Attempt to peel out zero iterations?\""
, "/build/llvm-toolchain-snapshot-12~++20210125100614+2cdb34efdac5/llvm/lib/Transforms/Utils/LoopPeel.cpp"
, 663, __PRETTY_FUNCTION__));
1
Assuming 'PeelCount' is > 0
→
2
←
'?' condition is true
→
664 assert(canPeel(L) && "Attempt to peel a loop which is not peelable?")((canPeel(L) && "Attempt to peel a loop which is not peelable?"
) ? static_cast<void> (0) : __assert_fail ("canPeel(L) && \"Attempt to peel a loop which is not peelable?\""
, "/build/llvm-toolchain-snapshot-12~++20210125100614+2cdb34efdac5/llvm/lib/Transforms/Utils/LoopPeel.cpp"
, 664, __PRETTY_FUNCTION__));
3
←
'?' condition is true
→
665
666 LoopBlocksDFS LoopBlocks(L);
667 LoopBlocks.perform(LI);
668
669 BasicBlock *Header = L->getHeader();
670 BasicBlock *PreHeader = L->getLoopPreheader();
671 BasicBlock *Latch = L->getLoopLatch();
672 SmallVector<std::pair<BasicBlock *, BasicBlock *>, 4> ExitEdges;
673 L->getExitEdges(ExitEdges);
674
675 DenseMap<BasicBlock *, BasicBlock *> ExitIDom;
676 if (DT) {
4
←
Assuming 'DT' is null
→
5
←
Taking false branch
→
677 // We'd like to determine the idom of exit block after peeling one
678 // iteration.
679 // Let Exit is exit block.
680 // Let ExitingSet - is a set of predecessors of Exit block. They are exiting
681 // blocks.
682 // Let Latch' and ExitingSet' are copies after a peeling.
683 // We'd like to find an idom'(Exit) - idom of Exit after peeling.
684 // It is an evident that idom'(Exit) will be the nearest common dominator
685 // of ExitingSet and ExitingSet'.
686 // idom(Exit) is a nearest common dominator of ExitingSet.
687 // idom(Exit)' is a nearest common dominator of ExitingSet'.
688 // Taking into account that we have a single Latch, Latch' will dominate
689 // Header and idom(Exit).
690 // So the idom'(Exit) is nearest common dominator of idom(Exit)' and Latch'.
691 // All these basic blocks are in the same loop, so what we find is
692 // (nearest common dominator of idom(Exit) and Latch)'.
693 // In the loop below we remember nearest common dominator of idom(Exit) and
694 // Latch to update idom of Exit later.
695 assert(L->hasDedicatedExits() && "No dedicated exits?")((L->hasDedicatedExits() && "No dedicated exits?")
? static_cast<void> (0) : __assert_fail ("L->hasDedicatedExits() && \"No dedicated exits?\""
, "/build/llvm-toolchain-snapshot-12~++20210125100614+2cdb34efdac5/llvm/lib/Transforms/Utils/LoopPeel.cpp"
, 695, __PRETTY_FUNCTION__));
696 for (auto Edge : ExitEdges) {
697 if (ExitIDom.count(Edge.second))
698 continue;
699 BasicBlock *BB = DT->findNearestCommonDominator(
700 DT->getNode(Edge.second)->getIDom()->getBlock(), Latch);
701 assert(L->contains(BB) && "IDom is not in a loop")((L->contains(BB) && "IDom is not in a loop") ? static_cast
<void> (0) : __assert_fail ("L->contains(BB) && \"IDom is not in a loop\""
, "/build/llvm-toolchain-snapshot-12~++20210125100614+2cdb34efdac5/llvm/lib/Transforms/Utils/LoopPeel.cpp"
, 701, __PRETTY_FUNCTION__));
702 ExitIDom[Edge.second] = BB;
703 }
704 }
705
706 Function *F = Header->getParent();
707
708 // Set up all the necessary basic blocks. It is convenient to split the
709 // preheader into 3 parts - two blocks to anchor the peeled copy of the loop
710 // body, and a new preheader for the "real" loop.
711
712 // Peeling the first iteration transforms.
713 //
714 // PreHeader:
715 // ...
716 // Header:
717 // LoopBody
718 // If (cond) goto Header
719 // Exit:
720 //
721 // into
722 //
723 // InsertTop:
724 // LoopBody
725 // If (!cond) goto Exit
726 // InsertBot:
727 // NewPreHeader:
728 // ...
729 // Header:
730 // LoopBody
731 // If (cond) goto Header
732 // Exit:
733 //
734 // Each following iteration will split the current bottom anchor in two,
735 // and put the new copy of the loop body between these two blocks. That is,
736 // after peeling another iteration from the example above, we'll split
737 // InsertBot, and get:
738 //
739 // InsertTop:
740 // LoopBody
741 // If (!cond) goto Exit
742 // InsertBot:
743 // LoopBody
744 // If (!cond) goto Exit
745 // InsertBot.next:
746 // NewPreHeader:
747 // ...
748 // Header:
749 // LoopBody
750 // If (cond) goto Header
751 // Exit:
752
753 BasicBlock *InsertTop = SplitEdge(PreHeader, Header, DT, LI);
754 BasicBlock *InsertBot =
755 SplitBlock(InsertTop, InsertTop->getTerminator(), DT, LI);
756 BasicBlock *NewPreHeader =
757 SplitBlock(InsertBot, InsertBot->getTerminator(), DT, LI);
758
759 InsertTop->setName(Header->getName() + ".peel.begin");
760 InsertBot->setName(Header->getName() + ".peel.next");
761 NewPreHeader->setName(PreHeader->getName() + ".peel.newph");
762
763 ValueToValueMapTy LVMap;
764
765 // If we have branch weight information, we'll want to update it for the
766 // newly created branches.
767 BranchInst *LatchBR =
768 cast<BranchInst>(cast<BasicBlock>(Latch)->getTerminator());
6
←
'Latch' is a 'BasicBlock'
→
7
←
The object is a 'BranchInst'
→
769 uint64_t ExitWeight = 0, FallThroughWeight = 0;
770 initBranchWeights(Header, LatchBR, ExitWeight, FallThroughWeight);
771
772 // For each peeled-off iteration, make a copy of the loop.
773 for (unsigned Iter = 0; Iter
7.1
'Iter' is < 'PeelCount'
 < PeelCount; ++Iter) {
8
←
Loop condition is true. Entering loop body
→
10
←
Assuming 'Iter' is >= 'PeelCount'
→
11
←
Loop condition is false. Execution continues on line 814
→
774 SmallVector<BasicBlock *, 8> NewBlocks;
775 ValueToValueMapTy VMap;
776
777 cloneLoopBlocks(L, Iter, InsertTop, InsertBot, ExitEdges, NewBlocks,
778 LoopBlocks, VMap, LVMap, DT, LI);
779
780 // Remap to use values from the current iteration instead of the
781 // previous one.
782 remapInstructionsInBlocks(NewBlocks, VMap);
783
784 if (DT
8.1
'DT' is null
) {
9
←
Taking false branch
→
785 // Latches of the cloned loops dominate over the loop exit, so idom of the
786 // latter is the first cloned loop body, as original PreHeader dominates
787 // the original loop body.
788 if (Iter == 0)
789 for (auto Exit : ExitIDom)
790 DT->changeImmediateDominator(Exit.first,
791 cast<BasicBlock>(LVMap[Exit.second]));
792#ifdef EXPENSIVE_CHECKS
793 assert(DT->verify(DominatorTree::VerificationLevel::Fast))((DT->verify(DominatorTree::VerificationLevel::Fast)) ? static_cast
<void> (0) : __assert_fail ("DT->verify(DominatorTree::VerificationLevel::Fast)"
, "/build/llvm-toolchain-snapshot-12~++20210125100614+2cdb34efdac5/llvm/lib/Transforms/Utils/LoopPeel.cpp"
, 793, __PRETTY_FUNCTION__));
794#endif
795 }
796
797 auto *LatchBRCopy = cast<BranchInst>(VMap[LatchBR]);
798 updateBranchWeights(InsertBot, LatchBRCopy, ExitWeight, FallThroughWeight);
799 // Remove Loop metadata from the latch branch instruction
800 // because it is not the Loop's latch branch anymore.
801 LatchBRCopy->setMetadata(LLVMContext::MD_loop, nullptr);
802
803 InsertTop = InsertBot;
804 InsertBot = SplitBlock(InsertBot, InsertBot->getTerminator(), DT, LI);
805 InsertBot->setName(Header->getName() + ".peel.next");
806
807 F->getBasicBlockList().splice(InsertTop->getIterator(),
808 F->getBasicBlockList(),
809 NewBlocks[0]->getIterator(), F->end());
810 }
811
812 // Now adjust the phi nodes in the loop header to get their initial values
813 // from the last peeled-off iteration instead of the preheader.
814 for (BasicBlock::iterator I = Header->begin(); isa<PHINode>(I); ++I) {
12
←
Assuming 'I' is not a 'PHINode'
→
13
←
Loop condition is false. Execution continues on line 824
→
815 PHINode *PHI = cast<PHINode>(I);
816 Value *NewVal = PHI->getIncomingValueForBlock(Latch);
817 Instruction *LatchInst = dyn_cast<Instruction>(NewVal);
818 if (LatchInst && L->contains(LatchInst))
819 NewVal = LVMap[LatchInst];
820
821 PHI->setIncomingValueForBlock(NewPreHeader, NewVal);
822 }
823
824 fixupBranchWeights(Header, LatchBR, ExitWeight, FallThroughWeight);
825
826 // Update Metadata for count of peeled off iterations.
827 unsigned AlreadyPeeled = 0;
828 if (auto Peeled = getOptionalIntLoopAttribute(L, PeeledCountMetaData))
14
←
Assuming the condition is false
→
15
←
Taking false branch
→
829 AlreadyPeeled = *Peeled;
830 addStringMetadataToLoop(L, PeeledCountMetaData, AlreadyPeeled + PeelCount);
831
832 if (Loop *ParentLoop = L->getParentLoop())
16
←
Assuming 'ParentLoop' is null
→
17
←
Taking false branch
→
833 L = ParentLoop;
834
835 // We modified the loop, update SE.
836 SE->forgetTopmostLoop(L);
837
838 // Finally DomtTree must be correct.
839 assert(DT->verify(DominatorTree::VerificationLevel::Fast))((DT->verify(DominatorTree::VerificationLevel::Fast)) ? static_cast
<void> (0) : __assert_fail ("DT->verify(DominatorTree::VerificationLevel::Fast)"
, "/build/llvm-toolchain-snapshot-12~++20210125100614+2cdb34efdac5/llvm/lib/Transforms/Utils/LoopPeel.cpp"
, 839, __PRETTY_FUNCTION__));
18
←
Called C++ object pointer is null
840
841 // FIXME: Incrementally update loop-simplify
842 simplifyLoop(L, DT, LI, SE, AC, nullptr, PreserveLCSSA);
843
844 NumPeeled++;
845
846 return true;
847}