Bug Summary

File:llvm/lib/Transforms/Utils/LoopPeel.cpp
Warning:line 834, column 3
Called C++ object pointer is null

Annotated Source Code

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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 -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~++20201129111111+e987fbdd85d/build-llvm/lib/Transforms/Utils -I /build/llvm-toolchain-snapshot-12~++20201129111111+e987fbdd85d/llvm/lib/Transforms/Utils -I /build/llvm-toolchain-snapshot-12~++20201129111111+e987fbdd85d/build-llvm/include -I /build/llvm-toolchain-snapshot-12~++20201129111111+e987fbdd85d/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~++20201129111111+e987fbdd85d/build-llvm/lib/Transforms/Utils -fdebug-prefix-map=/build/llvm-toolchain-snapshot-12~++20201129111111+e987fbdd85d=. -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-2020-11-29-190409-37574-1 -x c++ /build/llvm-toolchain-snapshot-12~++20201129111111+e987fbdd85d/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 if (L->getLoopLatch() != L->getExitingBlock())
119 return false;
120
121 return true;
122}
123
124// This function calculates the number of iterations after which the given Phi
125// becomes an invariant. The pre-calculated values are memorized in the map. The
126// function (shortcut is I) is calculated according to the following definition:
127// Given %x = phi <Inputs from above the loop>, ..., [%y, %back.edge].
128// If %y is a loop invariant, then I(%x) = 1.
129// If %y is a Phi from the loop header, I(%x) = I(%y) + 1.
130// Otherwise, I(%x) is infinite.
131// TODO: Actually if %y is an expression that depends only on Phi %z and some
132// loop invariants, we can estimate I(%x) = I(%z) + 1. The example
133// looks like:
134// %x = phi(0, %a), <-- becomes invariant starting from 3rd iteration.
135// %y = phi(0, 5),
136// %a = %y + 1.
137static unsigned calculateIterationsToInvariance(
138 PHINode *Phi, Loop *L, BasicBlock *BackEdge,
139 SmallDenseMap<PHINode *, unsigned> &IterationsToInvariance) {
140 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~++20201129111111+e987fbdd85d/llvm/lib/Transforms/Utils/LoopPeel.cpp"
, 141, __PRETTY_FUNCTION__))
141 "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~++20201129111111+e987fbdd85d/llvm/lib/Transforms/Utils/LoopPeel.cpp"
, 141, __PRETTY_FUNCTION__))
;
142 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~++20201129111111+e987fbdd85d/llvm/lib/Transforms/Utils/LoopPeel.cpp"
, 142, __PRETTY_FUNCTION__))
;
143 // If we already know the answer, take it from the map.
144 auto I = IterationsToInvariance.find(Phi);
145 if (I != IterationsToInvariance.end())
146 return I->second;
147
148 // Otherwise we need to analyze the input from the back edge.
149 Value *Input = Phi->getIncomingValueForBlock(BackEdge);
150 // Place infinity to map to avoid infinite recursion for cycled Phis. Such
151 // cycles can never stop on an invariant.
152 IterationsToInvariance[Phi] = InfiniteIterationsToInvariance;
153 unsigned ToInvariance = InfiniteIterationsToInvariance;
154
155 if (L->isLoopInvariant(Input))
156 ToInvariance = 1u;
157 else if (PHINode *IncPhi = dyn_cast<PHINode>(Input)) {
158 // Only consider Phis in header block.
159 if (IncPhi->getParent() != L->getHeader())
160 return InfiniteIterationsToInvariance;
161 // If the input becomes an invariant after X iterations, then our Phi
162 // becomes an invariant after X + 1 iterations.
163 unsigned InputToInvariance = calculateIterationsToInvariance(
164 IncPhi, L, BackEdge, IterationsToInvariance);
165 if (InputToInvariance != InfiniteIterationsToInvariance)
166 ToInvariance = InputToInvariance + 1u;
167 }
168
169 // If we found that this Phi lies in an invariant chain, update the map.
170 if (ToInvariance != InfiniteIterationsToInvariance)
171 IterationsToInvariance[Phi] = ToInvariance;
172 return ToInvariance;
173}
174
175// Return the number of iterations to peel off that make conditions in the
176// body true/false. For example, if we peel 2 iterations off the loop below,
177// the condition i < 2 can be evaluated at compile time.
178// for (i = 0; i < n; i++)
179// if (i < 2)
180// ..
181// else
182// ..
183// }
184static unsigned countToEliminateCompares(Loop &L, unsigned MaxPeelCount,
185 ScalarEvolution &SE) {
186 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~++20201129111111+e987fbdd85d/llvm/lib/Transforms/Utils/LoopPeel.cpp"
, 186, __PRETTY_FUNCTION__))
;
187 unsigned DesiredPeelCount = 0;
188
189 for (auto *BB : L.blocks()) {
190 auto *BI = dyn_cast<BranchInst>(BB->getTerminator());
191 if (!BI || BI->isUnconditional())
192 continue;
193
194 // Ignore loop exit condition.
195 if (L.getLoopLatch() == BB)
196 continue;
197
198 Value *Condition = BI->getCondition();
199 Value *LeftVal, *RightVal;
200 CmpInst::Predicate Pred;
201 if (!match(Condition, m_ICmp(Pred, m_Value(LeftVal), m_Value(RightVal))))
202 continue;
203
204 const SCEV *LeftSCEV = SE.getSCEV(LeftVal);
205 const SCEV *RightSCEV = SE.getSCEV(RightVal);
206
207 // Do not consider predicates that are known to be true or false
208 // independently of the loop iteration.
209 if (SE.isKnownPredicate(Pred, LeftSCEV, RightSCEV) ||
210 SE.isKnownPredicate(ICmpInst::getInversePredicate(Pred), LeftSCEV,
211 RightSCEV))
212 continue;
213
214 // Check if we have a condition with one AddRec and one non AddRec
215 // expression. Normalize LeftSCEV to be the AddRec.
216 if (!isa<SCEVAddRecExpr>(LeftSCEV)) {
217 if (isa<SCEVAddRecExpr>(RightSCEV)) {
218 std::swap(LeftSCEV, RightSCEV);
219 Pred = ICmpInst::getSwappedPredicate(Pred);
220 } else
221 continue;
222 }
223
224 const SCEVAddRecExpr *LeftAR = cast<SCEVAddRecExpr>(LeftSCEV);
225
226 // Avoid huge SCEV computations in the loop below, make sure we only
227 // consider AddRecs of the loop we are trying to peel.
228 if (!LeftAR->isAffine() || LeftAR->getLoop() != &L)
229 continue;
230 if (!(ICmpInst::isEquality(Pred) && LeftAR->hasNoSelfWrap()) &&
231 !SE.getMonotonicPredicateType(LeftAR, Pred))
232 continue;
233
234 // Check if extending the current DesiredPeelCount lets us evaluate Pred
235 // or !Pred in the loop body statically.
236 unsigned NewPeelCount = DesiredPeelCount;
237
238 const SCEV *IterVal = LeftAR->evaluateAtIteration(
239 SE.getConstant(LeftSCEV->getType(), NewPeelCount), SE);
240
241 // If the original condition is not known, get the negated predicate
242 // (which holds on the else branch) and check if it is known. This allows
243 // us to peel of iterations that make the original condition false.
244 if (!SE.isKnownPredicate(Pred, IterVal, RightSCEV))
245 Pred = ICmpInst::getInversePredicate(Pred);
246
247 const SCEV *Step = LeftAR->getStepRecurrence(SE);
248 const SCEV *NextIterVal = SE.getAddExpr(IterVal, Step);
249 auto PeelOneMoreIteration = [&IterVal, &NextIterVal, &SE, Step,
250 &NewPeelCount]() {
251 IterVal = NextIterVal;
252 NextIterVal = SE.getAddExpr(IterVal, Step);
253 NewPeelCount++;
254 };
255
256 auto CanPeelOneMoreIteration = [&NewPeelCount, &MaxPeelCount]() {
257 return NewPeelCount < MaxPeelCount;
258 };
259
260 while (CanPeelOneMoreIteration() &&
261 SE.isKnownPredicate(Pred, IterVal, RightSCEV))
262 PeelOneMoreIteration();
263
264 // With *that* peel count, does the predicate !Pred become known in the
265 // first iteration of the loop body after peeling?
266 if (!SE.isKnownPredicate(ICmpInst::getInversePredicate(Pred), IterVal,
267 RightSCEV))
268 continue; // If not, give up.
269
270 // However, for equality comparisons, that isn't always sufficient to
271 // eliminate the comparsion in loop body, we may need to peel one more
272 // iteration. See if that makes !Pred become unknown again.
273 if (ICmpInst::isEquality(Pred) &&
274 !SE.isKnownPredicate(ICmpInst::getInversePredicate(Pred), NextIterVal,
275 RightSCEV) &&
276 !SE.isKnownPredicate(Pred, IterVal, RightSCEV) &&
277 SE.isKnownPredicate(Pred, NextIterVal, RightSCEV)) {
278 if (!CanPeelOneMoreIteration())
279 continue; // Need to peel one more iteration, but can't. Give up.
280 PeelOneMoreIteration(); // Great!
281 }
282
283 DesiredPeelCount = std::max(DesiredPeelCount, NewPeelCount);
284 }
285
286 return DesiredPeelCount;
287}
288
289// Return the number of iterations we want to peel off.
290void llvm::computePeelCount(Loop *L, unsigned LoopSize,
291 TargetTransformInfo::PeelingPreferences &PP,
292 unsigned &TripCount, ScalarEvolution &SE,
293 unsigned Threshold) {
294 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~++20201129111111+e987fbdd85d/llvm/lib/Transforms/Utils/LoopPeel.cpp"
, 294, __PRETTY_FUNCTION__))
;
295 // Save the PP.PeelCount value set by the target in
296 // TTI.getPeelingPreferences or by the flag -unroll-peel-count.
297 unsigned TargetPeelCount = PP.PeelCount;
298 PP.PeelCount = 0;
299 if (!canPeel(L))
300 return;
301
302 // Only try to peel innermost loops by default.
303 // The constraint can be relaxed by the target in TTI.getUnrollingPreferences
304 // or by the flag -unroll-allow-loop-nests-peeling.
305 if (!PP.AllowLoopNestsPeeling && !L->isInnermost())
306 return;
307
308 // If the user provided a peel count, use that.
309 bool UserPeelCount = UnrollForcePeelCount.getNumOccurrences() > 0;
310 if (UserPeelCount) {
311 LLVM_DEBUG(dbgs() << "Force-peeling first " << UnrollForcePeelCountdo { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-peel")) { dbgs() << "Force-peeling first " <<
UnrollForcePeelCount << " iterations.\n"; } } while (false
)
312 << " iterations.\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-peel")) { dbgs() << "Force-peeling first " <<
UnrollForcePeelCount << " iterations.\n"; } } while (false
)
;
313 PP.PeelCount = UnrollForcePeelCount;
314 PP.PeelProfiledIterations = true;
315 return;
316 }
317
318 // Skip peeling if it's disabled.
319 if (!PP.AllowPeeling)
320 return;
321
322 unsigned AlreadyPeeled = 0;
323 if (auto Peeled = getOptionalIntLoopAttribute(L, PeeledCountMetaData))
324 AlreadyPeeled = *Peeled;
325 // Stop if we already peeled off the maximum number of iterations.
326 if (AlreadyPeeled >= UnrollPeelMaxCount)
327 return;
328
329 // Here we try to get rid of Phis which become invariants after 1, 2, ..., N
330 // iterations of the loop. For this we compute the number for iterations after
331 // which every Phi is guaranteed to become an invariant, and try to peel the
332 // maximum number of iterations among these values, thus turning all those
333 // Phis into invariants.
334 // First, check that we can peel at least one iteration.
335 if (2 * LoopSize <= Threshold && UnrollPeelMaxCount > 0) {
336 // Store the pre-calculated values here.
337 SmallDenseMap<PHINode *, unsigned> IterationsToInvariance;
338 // Now go through all Phis to calculate their the number of iterations they
339 // need to become invariants.
340 // Start the max computation with the UP.PeelCount value set by the target
341 // in TTI.getUnrollingPreferences or by the flag -unroll-peel-count.
342 unsigned DesiredPeelCount = TargetPeelCount;
343 BasicBlock *BackEdge = L->getLoopLatch();
344 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~++20201129111111+e987fbdd85d/llvm/lib/Transforms/Utils/LoopPeel.cpp"
, 344, __PRETTY_FUNCTION__))
;
345 for (auto BI = L->getHeader()->begin(); isa<PHINode>(&*BI); ++BI) {
346 PHINode *Phi = cast<PHINode>(&*BI);
347 unsigned ToInvariance = calculateIterationsToInvariance(
348 Phi, L, BackEdge, IterationsToInvariance);
349 if (ToInvariance != InfiniteIterationsToInvariance)
350 DesiredPeelCount = std::max(DesiredPeelCount, ToInvariance);
351 }
352
353 // Pay respect to limitations implied by loop size and the max peel count.
354 unsigned MaxPeelCount = UnrollPeelMaxCount;
355 MaxPeelCount = std::min(MaxPeelCount, Threshold / LoopSize - 1);
356
357 DesiredPeelCount = std::max(DesiredPeelCount,
358 countToEliminateCompares(*L, MaxPeelCount, SE));
359
360 if (DesiredPeelCount > 0) {
361 DesiredPeelCount = std::min(DesiredPeelCount, MaxPeelCount);
362 // Consider max peel count limitation.
363 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~++20201129111111+e987fbdd85d/llvm/lib/Transforms/Utils/LoopPeel.cpp"
, 363, __PRETTY_FUNCTION__))
;
364 if (DesiredPeelCount + AlreadyPeeled <= UnrollPeelMaxCount) {
365 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)
366 << " 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)
367 << " 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)
;
368 PP.PeelCount = DesiredPeelCount;
369 PP.PeelProfiledIterations = false;
370 return;
371 }
372 }
373 }
374
375 // Bail if we know the statically calculated trip count.
376 // In this case we rather prefer partial unrolling.
377 if (TripCount)
378 return;
379
380 // Do not apply profile base peeling if it is disabled.
381 if (!PP.PeelProfiledIterations)
382 return;
383 // If we don't know the trip count, but have reason to believe the average
384 // trip count is low, peeling should be beneficial, since we will usually
385 // hit the peeled section.
386 // We only do this in the presence of profile information, since otherwise
387 // our estimates of the trip count are not reliable enough.
388 if (L->getHeader()->getParent()->hasProfileData()) {
389 Optional<unsigned> PeelCount = getLoopEstimatedTripCount(L);
390 if (!PeelCount)
391 return;
392
393 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)
394 << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-peel")) { dbgs() << "Profile-based estimated trip count is "
<< *PeelCount << "\n"; } } while (false)
;
395
396 if (*PeelCount) {
397 if ((*PeelCount + AlreadyPeeled <= UnrollPeelMaxCount) &&
398 (LoopSize * (*PeelCount + 1) <= Threshold)) {
399 LLVM_DEBUG(dbgs() << "Peeling first " << *PeelCountdo { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-peel")) { dbgs() << "Peeling first " << *PeelCount
<< " iterations.\n"; } } while (false)
400 << " iterations.\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-peel")) { dbgs() << "Peeling first " << *PeelCount
<< " iterations.\n"; } } while (false)
;
401 PP.PeelCount = *PeelCount;
402 return;
403 }
404 LLVM_DEBUG(dbgs() << "Requested peel count: " << *PeelCount << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-peel")) { dbgs() << "Requested peel count: " <<
*PeelCount << "\n"; } } while (false)
;
405 LLVM_DEBUG(dbgs() << "Already peel count: " << AlreadyPeeled << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-peel")) { dbgs() << "Already peel count: " <<
AlreadyPeeled << "\n"; } } while (false)
;
406 LLVM_DEBUG(dbgs() << "Max peel count: " << UnrollPeelMaxCount << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-peel")) { dbgs() << "Max peel count: " << UnrollPeelMaxCount
<< "\n"; } } while (false)
;
407 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)
408 << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-peel")) { dbgs() << "Peel cost: " << LoopSize
* (*PeelCount + 1) << "\n"; } } while (false)
;
409 LLVM_DEBUG(dbgs() << "Max peel cost: " << Threshold << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-peel")) { dbgs() << "Max peel cost: " << Threshold
<< "\n"; } } while (false)
;
410 }
411 }
412}
413
414/// Update the branch weights of the latch of a peeled-off loop
415/// iteration.
416/// This sets the branch weights for the latch of the recently peeled off loop
417/// iteration correctly.
418/// Let F is a weight of the edge from latch to header.
419/// Let E is a weight of the edge from latch to exit.
420/// F/(F+E) is a probability to go to loop and E/(F+E) is a probability to
421/// go to exit.
422/// Then, Estimated TripCount = F / E.
423/// For I-th (counting from 0) peeled off iteration we set the the weights for
424/// the peeled latch as (TC - I, 1). It gives us reasonable distribution,
425/// The probability to go to exit 1/(TC-I) increases. At the same time
426/// the estimated trip count of remaining loop reduces by I.
427/// To avoid dealing with division rounding we can just multiple both part
428/// of weights to E and use weight as (F - I * E, E).
429///
430/// \param Header The copy of the header block that belongs to next iteration.
431/// \param LatchBR The copy of the latch branch that belongs to this iteration.
432/// \param[in,out] FallThroughWeight The weight of the edge from latch to
433/// header before peeling (in) and after peeled off one iteration (out).
434static void updateBranchWeights(BasicBlock *Header, BranchInst *LatchBR,
435 uint64_t ExitWeight,
436 uint64_t &FallThroughWeight) {
437 // FallThroughWeight is 0 means that there is no branch weights on original
438 // latch block or estimated trip count is zero.
439 if (!FallThroughWeight)
440 return;
441
442 unsigned HeaderIdx = (LatchBR->getSuccessor(0) == Header ? 0 : 1);
443 MDBuilder MDB(LatchBR->getContext());
444 MDNode *WeightNode =
445 HeaderIdx ? MDB.createBranchWeights(ExitWeight, FallThroughWeight)
446 : MDB.createBranchWeights(FallThroughWeight, ExitWeight);
447 LatchBR->setMetadata(LLVMContext::MD_prof, WeightNode);
448 FallThroughWeight =
449 FallThroughWeight > ExitWeight ? FallThroughWeight - ExitWeight : 1;
450}
451
452/// Initialize the weights.
453///
454/// \param Header The header block.
455/// \param LatchBR The latch branch.
456/// \param[out] ExitWeight The weight of the edge from Latch to Exit.
457/// \param[out] FallThroughWeight The weight of the edge from Latch to Header.
458static void initBranchWeights(BasicBlock *Header, BranchInst *LatchBR,
459 uint64_t &ExitWeight,
460 uint64_t &FallThroughWeight) {
461 uint64_t TrueWeight, FalseWeight;
462 if (!LatchBR->extractProfMetadata(TrueWeight, FalseWeight))
463 return;
464 unsigned HeaderIdx = LatchBR->getSuccessor(0) == Header ? 0 : 1;
465 ExitWeight = HeaderIdx ? TrueWeight : FalseWeight;
466 FallThroughWeight = HeaderIdx ? FalseWeight : TrueWeight;
467}
468
469/// Update the weights of original Latch block after peeling off all iterations.
470///
471/// \param Header The header block.
472/// \param LatchBR The latch branch.
473/// \param ExitWeight The weight of the edge from Latch to Exit.
474/// \param FallThroughWeight The weight of the edge from Latch to Header.
475static void fixupBranchWeights(BasicBlock *Header, BranchInst *LatchBR,
476 uint64_t ExitWeight,
477 uint64_t FallThroughWeight) {
478 // FallThroughWeight is 0 means that there is no branch weights on original
479 // latch block or estimated trip count is zero.
480 if (!FallThroughWeight)
481 return;
482
483 // Sets the branch weights on the loop exit.
484 MDBuilder MDB(LatchBR->getContext());
485 unsigned HeaderIdx = LatchBR->getSuccessor(0) == Header ? 0 : 1;
486 MDNode *WeightNode =
487 HeaderIdx ? MDB.createBranchWeights(ExitWeight, FallThroughWeight)
488 : MDB.createBranchWeights(FallThroughWeight, ExitWeight);
489 LatchBR->setMetadata(LLVMContext::MD_prof, WeightNode);
490}
491
492/// Clones the body of the loop L, putting it between \p InsertTop and \p
493/// InsertBot.
494/// \param IterNumber The serial number of the iteration currently being
495/// peeled off.
496/// \param ExitEdges The exit edges of the original loop.
497/// \param[out] NewBlocks A list of the blocks in the newly created clone
498/// \param[out] VMap The value map between the loop and the new clone.
499/// \param LoopBlocks A helper for DFS-traversal of the loop.
500/// \param LVMap A value-map that maps instructions from the original loop to
501/// instructions in the last peeled-off iteration.
502static void cloneLoopBlocks(
503 Loop *L, unsigned IterNumber, BasicBlock *InsertTop, BasicBlock *InsertBot,
504 SmallVectorImpl<std::pair<BasicBlock *, BasicBlock *>> &ExitEdges,
505 SmallVectorImpl<BasicBlock *> &NewBlocks, LoopBlocksDFS &LoopBlocks,
506 ValueToValueMapTy &VMap, ValueToValueMapTy &LVMap, DominatorTree *DT,
507 LoopInfo *LI) {
508 BasicBlock *Header = L->getHeader();
509 BasicBlock *Latch = L->getLoopLatch();
510 BasicBlock *PreHeader = L->getLoopPreheader();
511
512 Function *F = Header->getParent();
513 LoopBlocksDFS::RPOIterator BlockBegin = LoopBlocks.beginRPO();
514 LoopBlocksDFS::RPOIterator BlockEnd = LoopBlocks.endRPO();
515 Loop *ParentLoop = L->getParentLoop();
516
517 // For each block in the original loop, create a new copy,
518 // and update the value map with the newly created values.
519 for (LoopBlocksDFS::RPOIterator BB = BlockBegin; BB != BlockEnd; ++BB) {
520 BasicBlock *NewBB = CloneBasicBlock(*BB, VMap, ".peel", F);
521 NewBlocks.push_back(NewBB);
522
523 // If an original block is an immediate child of the loop L, its copy
524 // is a child of a ParentLoop after peeling. If a block is a child of
525 // a nested loop, it is handled in the cloneLoop() call below.
526 if (ParentLoop && LI->getLoopFor(*BB) == L)
527 ParentLoop->addBasicBlockToLoop(NewBB, *LI);
528
529 VMap[*BB] = NewBB;
530
531 // If dominator tree is available, insert nodes to represent cloned blocks.
532 if (DT) {
533 if (Header == *BB)
534 DT->addNewBlock(NewBB, InsertTop);
535 else {
536 DomTreeNode *IDom = DT->getNode(*BB)->getIDom();
537 // VMap must contain entry for IDom, as the iteration order is RPO.
538 DT->addNewBlock(NewBB, cast<BasicBlock>(VMap[IDom->getBlock()]));
539 }
540 }
541 }
542
543 // Recursively create the new Loop objects for nested loops, if any,
544 // to preserve LoopInfo.
545 for (Loop *ChildLoop : *L) {
546 cloneLoop(ChildLoop, ParentLoop, VMap, LI, nullptr);
547 }
548
549 // Hook-up the control flow for the newly inserted blocks.
550 // The new header is hooked up directly to the "top", which is either
551 // the original loop preheader (for the first iteration) or the previous
552 // iteration's exiting block (for every other iteration)
553 InsertTop->getTerminator()->setSuccessor(0, cast<BasicBlock>(VMap[Header]));
554
555 // Similarly, for the latch:
556 // The original exiting edge is still hooked up to the loop exit.
557 // The backedge now goes to the "bottom", which is either the loop's real
558 // header (for the last peeled iteration) or the copied header of the next
559 // iteration (for every other iteration)
560 BasicBlock *NewLatch = cast<BasicBlock>(VMap[Latch]);
561 BranchInst *LatchBR = cast<BranchInst>(NewLatch->getTerminator());
562 for (unsigned idx = 0, e = LatchBR->getNumSuccessors(); idx < e; ++idx)
563 if (LatchBR->getSuccessor(idx) == Header) {
564 LatchBR->setSuccessor(idx, InsertBot);
565 break;
566 }
567 if (DT)
568 DT->changeImmediateDominator(InsertBot, NewLatch);
569
570 // The new copy of the loop body starts with a bunch of PHI nodes
571 // that pick an incoming value from either the preheader, or the previous
572 // loop iteration. Since this copy is no longer part of the loop, we
573 // resolve this statically:
574 // For the first iteration, we use the value from the preheader directly.
575 // For any other iteration, we replace the phi with the value generated by
576 // the immediately preceding clone of the loop body (which represents
577 // the previous iteration).
578 for (BasicBlock::iterator I = Header->begin(); isa<PHINode>(I); ++I) {
579 PHINode *NewPHI = cast<PHINode>(VMap[&*I]);
580 if (IterNumber == 0) {
581 VMap[&*I] = NewPHI->getIncomingValueForBlock(PreHeader);
582 } else {
583 Value *LatchVal = NewPHI->getIncomingValueForBlock(Latch);
584 Instruction *LatchInst = dyn_cast<Instruction>(LatchVal);
585 if (LatchInst && L->contains(LatchInst))
586 VMap[&*I] = LVMap[LatchInst];
587 else
588 VMap[&*I] = LatchVal;
589 }
590 cast<BasicBlock>(VMap[Header])->getInstList().erase(NewPHI);
591 }
592
593 // Fix up the outgoing values - we need to add a value for the iteration
594 // we've just created. Note that this must happen *after* the incoming
595 // values are adjusted, since the value going out of the latch may also be
596 // a value coming into the header.
597 for (auto Edge : ExitEdges)
598 for (PHINode &PHI : Edge.second->phis()) {
599 Value *LatchVal = PHI.getIncomingValueForBlock(Edge.first);
600 Instruction *LatchInst = dyn_cast<Instruction>(LatchVal);
601 if (LatchInst && L->contains(LatchInst))
602 LatchVal = VMap[LatchVal];
603 PHI.addIncoming(LatchVal, cast<BasicBlock>(VMap[Edge.first]));
604 }
605
606 // LastValueMap is updated with the values for the current loop
607 // which are used the next time this function is called.
608 for (auto KV : VMap)
609 LVMap[KV.first] = KV.second;
610}
611
612TargetTransformInfo::PeelingPreferences llvm::gatherPeelingPreferences(
613 Loop *L, ScalarEvolution &SE, const TargetTransformInfo &TTI,
614 Optional<bool> UserAllowPeeling,
615 Optional<bool> UserAllowProfileBasedPeeling, bool UnrollingSpecficValues) {
616 TargetTransformInfo::PeelingPreferences PP;
617
618 // Set the default values.
619 PP.PeelCount = 0;
620 PP.AllowPeeling = true;
621 PP.AllowLoopNestsPeeling = false;
622 PP.PeelProfiledIterations = true;
623
624 // Get the target specifc values.
625 TTI.getPeelingPreferences(L, SE, PP);
626
627 // User specified values using cl::opt.
628 if (UnrollingSpecficValues) {
629 if (UnrollPeelCount.getNumOccurrences() > 0)
630 PP.PeelCount = UnrollPeelCount;
631 if (UnrollAllowPeeling.getNumOccurrences() > 0)
632 PP.AllowPeeling = UnrollAllowPeeling;
633 if (UnrollAllowLoopNestsPeeling.getNumOccurrences() > 0)
634 PP.AllowLoopNestsPeeling = UnrollAllowLoopNestsPeeling;
635 }
636
637 // User specifed values provided by argument.
638 if (UserAllowPeeling.hasValue())
639 PP.AllowPeeling = *UserAllowPeeling;
640 if (UserAllowProfileBasedPeeling.hasValue())
641 PP.PeelProfiledIterations = *UserAllowProfileBasedPeeling;
642
643 return PP;
644}
645
646/// Peel off the first \p PeelCount iterations of loop \p L.
647///
648/// Note that this does not peel them off as a single straight-line block.
649/// Rather, each iteration is peeled off separately, and needs to check the
650/// exit condition.
651/// For loops that dynamically execute \p PeelCount iterations or less
652/// this provides a benefit, since the peeled off iterations, which account
653/// for the bulk of dynamic execution, can be further simplified by scalar
654/// optimizations.
655bool llvm::peelLoop(Loop *L, unsigned PeelCount, LoopInfo *LI,
656 ScalarEvolution *SE, DominatorTree *DT, AssumptionCache *AC,
657 bool PreserveLCSSA) {
658 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~++20201129111111+e987fbdd85d/llvm/lib/Transforms/Utils/LoopPeel.cpp"
, 658, __PRETTY_FUNCTION__))
;
1
Assuming 'PeelCount' is > 0
2
'?' condition is true
659 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~++20201129111111+e987fbdd85d/llvm/lib/Transforms/Utils/LoopPeel.cpp"
, 659, __PRETTY_FUNCTION__))
;
3
'?' condition is true
660
661 LoopBlocksDFS LoopBlocks(L);
662 LoopBlocks.perform(LI);
663
664 BasicBlock *Header = L->getHeader();
665 BasicBlock *PreHeader = L->getLoopPreheader();
666 BasicBlock *Latch = L->getLoopLatch();
667 SmallVector<std::pair<BasicBlock *, BasicBlock *>, 4> ExitEdges;
668 L->getExitEdges(ExitEdges);
669
670 DenseMap<BasicBlock *, BasicBlock *> ExitIDom;
671 if (DT) {
4
Assuming 'DT' is null
5
Taking false branch
672 // We'd like to determine the idom of exit block after peeling one
673 // iteration.
674 // Let Exit is exit block.
675 // Let ExitingSet - is a set of predecessors of Exit block. They are exiting
676 // blocks.
677 // Let Latch' and ExitingSet' are copies after a peeling.
678 // We'd like to find an idom'(Exit) - idom of Exit after peeling.
679 // It is an evident that idom'(Exit) will be the nearest common dominator
680 // of ExitingSet and ExitingSet'.
681 // idom(Exit) is a nearest common dominator of ExitingSet.
682 // idom(Exit)' is a nearest common dominator of ExitingSet'.
683 // Taking into account that we have a single Latch, Latch' will dominate
684 // Header and idom(Exit).
685 // So the idom'(Exit) is nearest common dominator of idom(Exit)' and Latch'.
686 // All these basic blocks are in the same loop, so what we find is
687 // (nearest common dominator of idom(Exit) and Latch)'.
688 // In the loop below we remember nearest common dominator of idom(Exit) and
689 // Latch to update idom of Exit later.
690 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~++20201129111111+e987fbdd85d/llvm/lib/Transforms/Utils/LoopPeel.cpp"
, 690, __PRETTY_FUNCTION__))
;
691 for (auto Edge : ExitEdges) {
692 if (ExitIDom.count(Edge.second))
693 continue;
694 BasicBlock *BB = DT->findNearestCommonDominator(
695 DT->getNode(Edge.second)->getIDom()->getBlock(), Latch);
696 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~++20201129111111+e987fbdd85d/llvm/lib/Transforms/Utils/LoopPeel.cpp"
, 696, __PRETTY_FUNCTION__))
;
697 ExitIDom[Edge.second] = BB;
698 }
699 }
700
701 Function *F = Header->getParent();
702
703 // Set up all the necessary basic blocks. It is convenient to split the
704 // preheader into 3 parts - two blocks to anchor the peeled copy of the loop
705 // body, and a new preheader for the "real" loop.
706
707 // Peeling the first iteration transforms.
708 //
709 // PreHeader:
710 // ...
711 // Header:
712 // LoopBody
713 // If (cond) goto Header
714 // Exit:
715 //
716 // into
717 //
718 // InsertTop:
719 // LoopBody
720 // If (!cond) goto Exit
721 // InsertBot:
722 // NewPreHeader:
723 // ...
724 // Header:
725 // LoopBody
726 // If (cond) goto Header
727 // Exit:
728 //
729 // Each following iteration will split the current bottom anchor in two,
730 // and put the new copy of the loop body between these two blocks. That is,
731 // after peeling another iteration from the example above, we'll split
732 // InsertBot, and get:
733 //
734 // InsertTop:
735 // LoopBody
736 // If (!cond) goto Exit
737 // InsertBot:
738 // LoopBody
739 // If (!cond) goto Exit
740 // InsertBot.next:
741 // NewPreHeader:
742 // ...
743 // Header:
744 // LoopBody
745 // If (cond) goto Header
746 // Exit:
747
748 BasicBlock *InsertTop = SplitEdge(PreHeader, Header, DT, LI);
749 BasicBlock *InsertBot =
750 SplitBlock(InsertTop, InsertTop->getTerminator(), DT, LI);
751 BasicBlock *NewPreHeader =
752 SplitBlock(InsertBot, InsertBot->getTerminator(), DT, LI);
753
754 InsertTop->setName(Header->getName() + ".peel.begin");
755 InsertBot->setName(Header->getName() + ".peel.next");
756 NewPreHeader->setName(PreHeader->getName() + ".peel.newph");
757
758 ValueToValueMapTy LVMap;
759
760 // If we have branch weight information, we'll want to update it for the
761 // newly created branches.
762 BranchInst *LatchBR =
763 cast<BranchInst>(cast<BasicBlock>(Latch)->getTerminator());
6
'Latch' is a 'BasicBlock'
7
The object is a 'BranchInst'
764 uint64_t ExitWeight = 0, FallThroughWeight = 0;
765 initBranchWeights(Header, LatchBR, ExitWeight, FallThroughWeight);
766
767 // For each peeled-off iteration, make a copy of the loop.
768 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 809
769 SmallVector<BasicBlock *, 8> NewBlocks;
770 ValueToValueMapTy VMap;
771
772 cloneLoopBlocks(L, Iter, InsertTop, InsertBot, ExitEdges, NewBlocks,
773 LoopBlocks, VMap, LVMap, DT, LI);
774
775 // Remap to use values from the current iteration instead of the
776 // previous one.
777 remapInstructionsInBlocks(NewBlocks, VMap);
778
779 if (DT
8.1
'DT' is null
) {
9
Taking false branch
780 // Latches of the cloned loops dominate over the loop exit, so idom of the
781 // latter is the first cloned loop body, as original PreHeader dominates
782 // the original loop body.
783 if (Iter == 0)
784 for (auto Exit : ExitIDom)
785 DT->changeImmediateDominator(Exit.first,
786 cast<BasicBlock>(LVMap[Exit.second]));
787#ifdef EXPENSIVE_CHECKS
788 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~++20201129111111+e987fbdd85d/llvm/lib/Transforms/Utils/LoopPeel.cpp"
, 788, __PRETTY_FUNCTION__))
;
789#endif
790 }
791
792 auto *LatchBRCopy = cast<BranchInst>(VMap[LatchBR]);
793 updateBranchWeights(InsertBot, LatchBRCopy, ExitWeight, FallThroughWeight);
794 // Remove Loop metadata from the latch branch instruction
795 // because it is not the Loop's latch branch anymore.
796 LatchBRCopy->setMetadata(LLVMContext::MD_loop, nullptr);
797
798 InsertTop = InsertBot;
799 InsertBot = SplitBlock(InsertBot, InsertBot->getTerminator(), DT, LI);
800 InsertBot->setName(Header->getName() + ".peel.next");
801
802 F->getBasicBlockList().splice(InsertTop->getIterator(),
803 F->getBasicBlockList(),
804 NewBlocks[0]->getIterator(), F->end());
805 }
806
807 // Now adjust the phi nodes in the loop header to get their initial values
808 // from the last peeled-off iteration instead of the preheader.
809 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 819
810 PHINode *PHI = cast<PHINode>(I);
811 Value *NewVal = PHI->getIncomingValueForBlock(Latch);
812 Instruction *LatchInst = dyn_cast<Instruction>(NewVal);
813 if (LatchInst && L->contains(LatchInst))
814 NewVal = LVMap[LatchInst];
815
816 PHI->setIncomingValueForBlock(NewPreHeader, NewVal);
817 }
818
819 fixupBranchWeights(Header, LatchBR, ExitWeight, FallThroughWeight);
820
821 // Update Metadata for count of peeled off iterations.
822 unsigned AlreadyPeeled = 0;
823 if (auto Peeled = getOptionalIntLoopAttribute(L, PeeledCountMetaData))
14
Assuming the condition is false
15
Taking false branch
824 AlreadyPeeled = *Peeled;
825 addStringMetadataToLoop(L, PeeledCountMetaData, AlreadyPeeled + PeelCount);
826
827 if (Loop *ParentLoop = L->getParentLoop())
16
Assuming 'ParentLoop' is null
17
Taking false branch
828 L = ParentLoop;
829
830 // We modified the loop, update SE.
831 SE->forgetTopmostLoop(L);
832
833 // Finally DomtTree must be correct.
834 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~++20201129111111+e987fbdd85d/llvm/lib/Transforms/Utils/LoopPeel.cpp"
, 834, __PRETTY_FUNCTION__))
;
18
Called C++ object pointer is null
835
836 // FIXME: Incrementally update loop-simplify
837 simplifyLoop(L, DT, LI, SE, AC, nullptr, PreserveLCSSA);
838
839 NumPeeled++;
840
841 return true;
842}