Bug Summary

File:llvm/lib/Transforms/Utils/LoopUnrollPeel.cpp
Warning:line 790, column 3
Called C++ object pointer is null

Annotated Source Code

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clang -cc1 -triple x86_64-pc-linux-gnu -analyze -disable-free -disable-llvm-verifier -discard-value-names -main-file-name LoopUnrollPeel.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 -mthread-model posix -mframe-pointer=none -fmath-errno -fno-rounding-math -masm-verbose -mconstructor-aliases -munwind-tables -target-cpu x86-64 -dwarf-column-info -fno-split-dwarf-inlining -debugger-tuning=gdb -ffunction-sections -fdata-sections -resource-dir /usr/lib/llvm-11/lib/clang/11.0.0 -D _DEBUG -D _GNU_SOURCE -D __STDC_CONSTANT_MACROS -D __STDC_FORMAT_MACROS -D __STDC_LIMIT_MACROS -I /build/llvm-toolchain-snapshot-11~++20200309111110+2c36c23f347/build-llvm/lib/Transforms/Utils -I /build/llvm-toolchain-snapshot-11~++20200309111110+2c36c23f347/llvm/lib/Transforms/Utils -I /build/llvm-toolchain-snapshot-11~++20200309111110+2c36c23f347/build-llvm/include -I /build/llvm-toolchain-snapshot-11~++20200309111110+2c36c23f347/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-11/lib/clang/11.0.0/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-11~++20200309111110+2c36c23f347/build-llvm/lib/Transforms/Utils -fdebug-prefix-map=/build/llvm-toolchain-snapshot-11~++20200309111110+2c36c23f347=. -ferror-limit 19 -fmessage-length 0 -fvisibility-inlines-hidden -stack-protector 2 -fgnuc-version=4.2.1 -fobjc-runtime=gcc -fdiagnostics-show-option -vectorize-loops -vectorize-slp -analyzer-output=html -analyzer-config stable-report-filename=true -faddrsig -o /tmp/scan-build-2020-03-09-184146-41876-1 -x c++ /build/llvm-toolchain-snapshot-11~++20200309111110+2c36c23f347/llvm/lib/Transforms/Utils/LoopUnrollPeel.cpp
1//===- UnrollLoopPeel.cpp - Loop peeling utilities ------------------------===//
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// This file implements some loop unrolling utilities for peeling loops
10// with dynamically inferred (from PGO) trip counts. See LoopUnroll.cpp for
11// unrolling loops with compile-time constant trip counts.
12//
13//===----------------------------------------------------------------------===//
14
15#include "llvm/ADT/DenseMap.h"
16#include "llvm/ADT/Optional.h"
17#include "llvm/ADT/SmallVector.h"
18#include "llvm/ADT/Statistic.h"
19#include "llvm/Analysis/LoopInfo.h"
20#include "llvm/Analysis/LoopIterator.h"
21#include "llvm/Analysis/ScalarEvolution.h"
22#include "llvm/Analysis/ScalarEvolutionExpressions.h"
23#include "llvm/Analysis/TargetTransformInfo.h"
24#include "llvm/IR/BasicBlock.h"
25#include "llvm/IR/Dominators.h"
26#include "llvm/IR/Function.h"
27#include "llvm/IR/InstrTypes.h"
28#include "llvm/IR/Instruction.h"
29#include "llvm/IR/Instructions.h"
30#include "llvm/IR/LLVMContext.h"
31#include "llvm/IR/MDBuilder.h"
32#include "llvm/IR/Metadata.h"
33#include "llvm/IR/PatternMatch.h"
34#include "llvm/Support/Casting.h"
35#include "llvm/Support/CommandLine.h"
36#include "llvm/Support/Debug.h"
37#include "llvm/Support/raw_ostream.h"
38#include "llvm/Transforms/Utils/BasicBlockUtils.h"
39#include "llvm/Transforms/Utils/Cloning.h"
40#include "llvm/Transforms/Utils/LoopSimplify.h"
41#include "llvm/Transforms/Utils/LoopUtils.h"
42#include "llvm/Transforms/Utils/UnrollLoop.h"
43#include "llvm/Transforms/Utils/ValueMapper.h"
44#include <algorithm>
45#include <cassert>
46#include <cstdint>
47#include <limits>
48
49using namespace llvm;
50using namespace llvm::PatternMatch;
51
52#define DEBUG_TYPE"loop-unroll" "loop-unroll"
53
54STATISTIC(NumPeeled, "Number of loops peeled")static llvm::Statistic NumPeeled = {"loop-unroll", "NumPeeled"
, "Number of loops peeled"};
55
56static cl::opt<unsigned> UnrollPeelMaxCount(
57 "unroll-peel-max-count", cl::init(7), cl::Hidden,
58 cl::desc("Max average trip count which will cause loop peeling."));
59
60static cl::opt<unsigned> UnrollForcePeelCount(
61 "unroll-force-peel-count", cl::init(0), cl::Hidden,
62 cl::desc("Force a peel count regardless of profiling information."));
63
64static cl::opt<bool> UnrollPeelMultiDeoptExit(
65 "unroll-peel-multi-deopt-exit", cl::init(true), cl::Hidden,
66 cl::desc("Allow peeling of loops with multiple deopt exits."));
67
68static const char *PeeledCountMetaData = "llvm.loop.peeled.count";
69
70// Designates that a Phi is estimated to become invariant after an "infinite"
71// number of loop iterations (i.e. only may become an invariant if the loop is
72// fully unrolled).
73static const unsigned InfiniteIterationsToInvariance =
74 std::numeric_limits<unsigned>::max();
75
76// Check whether we are capable of peeling this loop.
77bool llvm::canPeel(Loop *L) {
78 // Make sure the loop is in simplified form
79 if (!L->isLoopSimplifyForm())
80 return false;
81
82 if (UnrollPeelMultiDeoptExit) {
83 SmallVector<BasicBlock *, 4> Exits;
84 L->getUniqueNonLatchExitBlocks(Exits);
85
86 if (!Exits.empty()) {
87 // Latch's terminator is a conditional branch, Latch is exiting and
88 // all non Latch exits ends up with deoptimize.
89 const BasicBlock *Latch = L->getLoopLatch();
90 const BranchInst *T = dyn_cast<BranchInst>(Latch->getTerminator());
91 return T && T->isConditional() && L->isLoopExiting(Latch) &&
92 all_of(Exits, [](const BasicBlock *BB) {
93 return BB->getTerminatingDeoptimizeCall();
94 });
95 }
96 }
97
98 // Only peel loops that contain a single exit
99 if (!L->getExitingBlock() || !L->getUniqueExitBlock())
100 return false;
101
102 // Don't try to peel loops where the latch is not the exiting block.
103 // This can be an indication of two different things:
104 // 1) The loop is not rotated.
105 // 2) The loop contains irreducible control flow that involves the latch.
106 if (L->getLoopLatch() != L->getExitingBlock())
107 return false;
108
109 return true;
110}
111
112// This function calculates the number of iterations after which the given Phi
113// becomes an invariant. The pre-calculated values are memorized in the map. The
114// function (shortcut is I) is calculated according to the following definition:
115// Given %x = phi <Inputs from above the loop>, ..., [%y, %back.edge].
116// If %y is a loop invariant, then I(%x) = 1.
117// If %y is a Phi from the loop header, I(%x) = I(%y) + 1.
118// Otherwise, I(%x) is infinite.
119// TODO: Actually if %y is an expression that depends only on Phi %z and some
120// loop invariants, we can estimate I(%x) = I(%z) + 1. The example
121// looks like:
122// %x = phi(0, %a), <-- becomes invariant starting from 3rd iteration.
123// %y = phi(0, 5),
124// %a = %y + 1.
125static unsigned calculateIterationsToInvariance(
126 PHINode *Phi, Loop *L, BasicBlock *BackEdge,
127 SmallDenseMap<PHINode *, unsigned> &IterationsToInvariance) {
128 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-11~++20200309111110+2c36c23f347/llvm/lib/Transforms/Utils/LoopUnrollPeel.cpp"
, 129, __PRETTY_FUNCTION__))
129 "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-11~++20200309111110+2c36c23f347/llvm/lib/Transforms/Utils/LoopUnrollPeel.cpp"
, 129, __PRETTY_FUNCTION__));
130 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-11~++20200309111110+2c36c23f347/llvm/lib/Transforms/Utils/LoopUnrollPeel.cpp"
, 130, __PRETTY_FUNCTION__));
131 // If we already know the answer, take it from the map.
132 auto I = IterationsToInvariance.find(Phi);
133 if (I != IterationsToInvariance.end())
134 return I->second;
135
136 // Otherwise we need to analyze the input from the back edge.
137 Value *Input = Phi->getIncomingValueForBlock(BackEdge);
138 // Place infinity to map to avoid infinite recursion for cycled Phis. Such
139 // cycles can never stop on an invariant.
140 IterationsToInvariance[Phi] = InfiniteIterationsToInvariance;
141 unsigned ToInvariance = InfiniteIterationsToInvariance;
142
143 if (L->isLoopInvariant(Input))
144 ToInvariance = 1u;
145 else if (PHINode *IncPhi = dyn_cast<PHINode>(Input)) {
146 // Only consider Phis in header block.
147 if (IncPhi->getParent() != L->getHeader())
148 return InfiniteIterationsToInvariance;
149 // If the input becomes an invariant after X iterations, then our Phi
150 // becomes an invariant after X + 1 iterations.
151 unsigned InputToInvariance = calculateIterationsToInvariance(
152 IncPhi, L, BackEdge, IterationsToInvariance);
153 if (InputToInvariance != InfiniteIterationsToInvariance)
154 ToInvariance = InputToInvariance + 1u;
155 }
156
157 // If we found that this Phi lies in an invariant chain, update the map.
158 if (ToInvariance != InfiniteIterationsToInvariance)
159 IterationsToInvariance[Phi] = ToInvariance;
160 return ToInvariance;
161}
162
163// Return the number of iterations to peel off that make conditions in the
164// body true/false. For example, if we peel 2 iterations off the loop below,
165// the condition i < 2 can be evaluated at compile time.
166// for (i = 0; i < n; i++)
167// if (i < 2)
168// ..
169// else
170// ..
171// }
172static unsigned countToEliminateCompares(Loop &L, unsigned MaxPeelCount,
173 ScalarEvolution &SE) {
174 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-11~++20200309111110+2c36c23f347/llvm/lib/Transforms/Utils/LoopUnrollPeel.cpp"
, 174, __PRETTY_FUNCTION__));
175 unsigned DesiredPeelCount = 0;
176
177 for (auto *BB : L.blocks()) {
178 auto *BI = dyn_cast<BranchInst>(BB->getTerminator());
179 if (!BI || BI->isUnconditional())
180 continue;
181
182 // Ignore loop exit condition.
183 if (L.getLoopLatch() == BB)
184 continue;
185
186 Value *Condition = BI->getCondition();
187 Value *LeftVal, *RightVal;
188 CmpInst::Predicate Pred;
189 if (!match(Condition, m_ICmp(Pred, m_Value(LeftVal), m_Value(RightVal))))
190 continue;
191
192 const SCEV *LeftSCEV = SE.getSCEV(LeftVal);
193 const SCEV *RightSCEV = SE.getSCEV(RightVal);
194
195 // Do not consider predicates that are known to be true or false
196 // independently of the loop iteration.
197 if (SE.isKnownPredicate(Pred, LeftSCEV, RightSCEV) ||
198 SE.isKnownPredicate(ICmpInst::getInversePredicate(Pred), LeftSCEV,
199 RightSCEV))
200 continue;
201
202 // Check if we have a condition with one AddRec and one non AddRec
203 // expression. Normalize LeftSCEV to be the AddRec.
204 if (!isa<SCEVAddRecExpr>(LeftSCEV)) {
205 if (isa<SCEVAddRecExpr>(RightSCEV)) {
206 std::swap(LeftSCEV, RightSCEV);
207 Pred = ICmpInst::getSwappedPredicate(Pred);
208 } else
209 continue;
210 }
211
212 const SCEVAddRecExpr *LeftAR = cast<SCEVAddRecExpr>(LeftSCEV);
213
214 // Avoid huge SCEV computations in the loop below, make sure we only
215 // consider AddRecs of the loop we are trying to peel.
216 if (!LeftAR->isAffine() || LeftAR->getLoop() != &L)
217 continue;
218 bool Increasing;
219 if (!(ICmpInst::isEquality(Pred) && LeftAR->hasNoSelfWrap()) &&
220 !SE.isMonotonicPredicate(LeftAR, Pred, Increasing))
221 continue;
222 (void)Increasing;
223
224 // Check if extending the current DesiredPeelCount lets us evaluate Pred
225 // or !Pred in the loop body statically.
226 unsigned NewPeelCount = DesiredPeelCount;
227
228 const SCEV *IterVal = LeftAR->evaluateAtIteration(
229 SE.getConstant(LeftSCEV->getType(), NewPeelCount), SE);
230
231 // If the original condition is not known, get the negated predicate
232 // (which holds on the else branch) and check if it is known. This allows
233 // us to peel of iterations that make the original condition false.
234 if (!SE.isKnownPredicate(Pred, IterVal, RightSCEV))
235 Pred = ICmpInst::getInversePredicate(Pred);
236
237 const SCEV *Step = LeftAR->getStepRecurrence(SE);
238 const SCEV *NextIterVal = SE.getAddExpr(IterVal, Step);
239 auto PeelOneMoreIteration = [&IterVal, &NextIterVal, &SE, Step,
240 &NewPeelCount]() {
241 IterVal = NextIterVal;
242 NextIterVal = SE.getAddExpr(IterVal, Step);
243 NewPeelCount++;
244 };
245
246 auto CanPeelOneMoreIteration = [&NewPeelCount, &MaxPeelCount]() {
247 return NewPeelCount < MaxPeelCount;
248 };
249
250 while (CanPeelOneMoreIteration() &&
251 SE.isKnownPredicate(Pred, IterVal, RightSCEV))
252 PeelOneMoreIteration();
253
254 // With *that* peel count, does the predicate !Pred become known in the
255 // first iteration of the loop body after peeling?
256 if (!SE.isKnownPredicate(ICmpInst::getInversePredicate(Pred), IterVal,
257 RightSCEV))
258 continue; // If not, give up.
259
260 // However, for equality comparisons, that isn't always sufficient to
261 // eliminate the comparsion in loop body, we may need to peel one more
262 // iteration. See if that makes !Pred become unknown again.
263 if (ICmpInst::isEquality(Pred) &&
264 !SE.isKnownPredicate(ICmpInst::getInversePredicate(Pred), NextIterVal,
265 RightSCEV)) {
266 assert(!SE.isKnownPredicate(Pred, IterVal, RightSCEV) &&((!SE.isKnownPredicate(Pred, IterVal, RightSCEV) && SE
.isKnownPredicate(Pred, NextIterVal, RightSCEV) && "Expected Pred to go from known to unknown."
) ? static_cast<void> (0) : __assert_fail ("!SE.isKnownPredicate(Pred, IterVal, RightSCEV) && SE.isKnownPredicate(Pred, NextIterVal, RightSCEV) && \"Expected Pred to go from known to unknown.\""
, "/build/llvm-toolchain-snapshot-11~++20200309111110+2c36c23f347/llvm/lib/Transforms/Utils/LoopUnrollPeel.cpp"
, 268, __PRETTY_FUNCTION__))
267 SE.isKnownPredicate(Pred, NextIterVal, RightSCEV) &&((!SE.isKnownPredicate(Pred, IterVal, RightSCEV) && SE
.isKnownPredicate(Pred, NextIterVal, RightSCEV) && "Expected Pred to go from known to unknown."
) ? static_cast<void> (0) : __assert_fail ("!SE.isKnownPredicate(Pred, IterVal, RightSCEV) && SE.isKnownPredicate(Pred, NextIterVal, RightSCEV) && \"Expected Pred to go from known to unknown.\""
, "/build/llvm-toolchain-snapshot-11~++20200309111110+2c36c23f347/llvm/lib/Transforms/Utils/LoopUnrollPeel.cpp"
, 268, __PRETTY_FUNCTION__))
268 "Expected Pred to go from known to unknown.")((!SE.isKnownPredicate(Pred, IterVal, RightSCEV) && SE
.isKnownPredicate(Pred, NextIterVal, RightSCEV) && "Expected Pred to go from known to unknown."
) ? static_cast<void> (0) : __assert_fail ("!SE.isKnownPredicate(Pred, IterVal, RightSCEV) && SE.isKnownPredicate(Pred, NextIterVal, RightSCEV) && \"Expected Pred to go from known to unknown.\""
, "/build/llvm-toolchain-snapshot-11~++20200309111110+2c36c23f347/llvm/lib/Transforms/Utils/LoopUnrollPeel.cpp"
, 268, __PRETTY_FUNCTION__));
269 if (!CanPeelOneMoreIteration())
270 continue; // Need to peel one more iteration, but can't. Give up.
271 PeelOneMoreIteration(); // Great!
272 }
273
274 DesiredPeelCount = std::max(DesiredPeelCount, NewPeelCount);
275 }
276
277 return DesiredPeelCount;
278}
279
280// Return the number of iterations we want to peel off.
281void llvm::computePeelCount(Loop *L, unsigned LoopSize,
282 TargetTransformInfo::UnrollingPreferences &UP,
283 unsigned &TripCount, ScalarEvolution &SE) {
284 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-11~++20200309111110+2c36c23f347/llvm/lib/Transforms/Utils/LoopUnrollPeel.cpp"
, 284, __PRETTY_FUNCTION__));
285 // Save the UP.PeelCount value set by the target in
286 // TTI.getUnrollingPreferences or by the flag -unroll-peel-count.
287 unsigned TargetPeelCount = UP.PeelCount;
288 UP.PeelCount = 0;
289 if (!canPeel(L))
290 return;
291
292 // Only try to peel innermost loops by default.
293 // The constraint can be relaxed by the target in TTI.getUnrollingPreferences
294 // or by the flag -unroll-allow-loop-nests-peeling.
295 if (!UP.AllowLoopNestsPeeling && !L->empty())
296 return;
297
298 // If the user provided a peel count, use that.
299 bool UserPeelCount = UnrollForcePeelCount.getNumOccurrences() > 0;
300 if (UserPeelCount) {
301 LLVM_DEBUG(dbgs() << "Force-peeling first " << UnrollForcePeelCountdo { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-unroll")) { dbgs() << "Force-peeling first " <<
UnrollForcePeelCount << " iterations.\n"; } } while (false
)
302 << " iterations.\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-unroll")) { dbgs() << "Force-peeling first " <<
UnrollForcePeelCount << " iterations.\n"; } } while (false
);
303 UP.PeelCount = UnrollForcePeelCount;
304 UP.PeelProfiledIterations = true;
305 return;
306 }
307
308 // Skip peeling if it's disabled.
309 if (!UP.AllowPeeling)
310 return;
311
312 unsigned AlreadyPeeled = 0;
313 if (auto Peeled = getOptionalIntLoopAttribute(L, PeeledCountMetaData))
314 AlreadyPeeled = *Peeled;
315 // Stop if we already peeled off the maximum number of iterations.
316 if (AlreadyPeeled >= UnrollPeelMaxCount)
317 return;
318
319 // Here we try to get rid of Phis which become invariants after 1, 2, ..., N
320 // iterations of the loop. For this we compute the number for iterations after
321 // which every Phi is guaranteed to become an invariant, and try to peel the
322 // maximum number of iterations among these values, thus turning all those
323 // Phis into invariants.
324 // First, check that we can peel at least one iteration.
325 if (2 * LoopSize <= UP.Threshold && UnrollPeelMaxCount > 0) {
326 // Store the pre-calculated values here.
327 SmallDenseMap<PHINode *, unsigned> IterationsToInvariance;
328 // Now go through all Phis to calculate their the number of iterations they
329 // need to become invariants.
330 // Start the max computation with the UP.PeelCount value set by the target
331 // in TTI.getUnrollingPreferences or by the flag -unroll-peel-count.
332 unsigned DesiredPeelCount = TargetPeelCount;
333 BasicBlock *BackEdge = L->getLoopLatch();
334 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-11~++20200309111110+2c36c23f347/llvm/lib/Transforms/Utils/LoopUnrollPeel.cpp"
, 334, __PRETTY_FUNCTION__));
335 for (auto BI = L->getHeader()->begin(); isa<PHINode>(&*BI); ++BI) {
336 PHINode *Phi = cast<PHINode>(&*BI);
337 unsigned ToInvariance = calculateIterationsToInvariance(
338 Phi, L, BackEdge, IterationsToInvariance);
339 if (ToInvariance != InfiniteIterationsToInvariance)
340 DesiredPeelCount = std::max(DesiredPeelCount, ToInvariance);
341 }
342
343 // Pay respect to limitations implied by loop size and the max peel count.
344 unsigned MaxPeelCount = UnrollPeelMaxCount;
345 MaxPeelCount = std::min(MaxPeelCount, UP.Threshold / LoopSize - 1);
346
347 DesiredPeelCount = std::max(DesiredPeelCount,
348 countToEliminateCompares(*L, MaxPeelCount, SE));
349
350 if (DesiredPeelCount > 0) {
351 DesiredPeelCount = std::min(DesiredPeelCount, MaxPeelCount);
352 // Consider max peel count limitation.
353 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-11~++20200309111110+2c36c23f347/llvm/lib/Transforms/Utils/LoopUnrollPeel.cpp"
, 353, __PRETTY_FUNCTION__));
354 if (DesiredPeelCount + AlreadyPeeled <= UnrollPeelMaxCount) {
355 LLVM_DEBUG(dbgs() << "Peel " << DesiredPeelCountdo { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-unroll")) { dbgs() << "Peel " << DesiredPeelCount
<< " iteration(s) to turn" << " some Phis into invariants.\n"
; } } while (false)
356 << " iteration(s) to turn"do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-unroll")) { dbgs() << "Peel " << DesiredPeelCount
<< " iteration(s) to turn" << " some Phis into invariants.\n"
; } } while (false)
357 << " some Phis into invariants.\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-unroll")) { dbgs() << "Peel " << DesiredPeelCount
<< " iteration(s) to turn" << " some Phis into invariants.\n"
; } } while (false);
358 UP.PeelCount = DesiredPeelCount;
359 UP.PeelProfiledIterations = false;
360 return;
361 }
362 }
363 }
364
365 // Bail if we know the statically calculated trip count.
366 // In this case we rather prefer partial unrolling.
367 if (TripCount)
368 return;
369
370 // Do not apply profile base peeling if it is disabled.
371 if (!UP.PeelProfiledIterations)
372 return;
373 // If we don't know the trip count, but have reason to believe the average
374 // trip count is low, peeling should be beneficial, since we will usually
375 // hit the peeled section.
376 // We only do this in the presence of profile information, since otherwise
377 // our estimates of the trip count are not reliable enough.
378 if (L->getHeader()->getParent()->hasProfileData()) {
379 Optional<unsigned> PeelCount = getLoopEstimatedTripCount(L);
380 if (!PeelCount)
381 return;
382
383 LLVM_DEBUG(dbgs() << "Profile-based estimated trip count is " << *PeelCountdo { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-unroll")) { dbgs() << "Profile-based estimated trip count is "
<< *PeelCount << "\n"; } } while (false)
384 << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-unroll")) { dbgs() << "Profile-based estimated trip count is "
<< *PeelCount << "\n"; } } while (false);
385
386 if (*PeelCount) {
387 if ((*PeelCount + AlreadyPeeled <= UnrollPeelMaxCount) &&
388 (LoopSize * (*PeelCount + 1) <= UP.Threshold)) {
389 LLVM_DEBUG(dbgs() << "Peeling first " << *PeelCountdo { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-unroll")) { dbgs() << "Peeling first " << *
PeelCount << " iterations.\n"; } } while (false)
390 << " iterations.\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-unroll")) { dbgs() << "Peeling first " << *
PeelCount << " iterations.\n"; } } while (false);
391 UP.PeelCount = *PeelCount;
392 return;
393 }
394 LLVM_DEBUG(dbgs() << "Requested peel count: " << *PeelCount << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-unroll")) { dbgs() << "Requested peel count: " <<
*PeelCount << "\n"; } } while (false);
395 LLVM_DEBUG(dbgs() << "Already peel count: " << AlreadyPeeled << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-unroll")) { dbgs() << "Already peel count: " <<
AlreadyPeeled << "\n"; } } while (false);
396 LLVM_DEBUG(dbgs() << "Max peel count: " << UnrollPeelMaxCount << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-unroll")) { dbgs() << "Max peel count: " <<
UnrollPeelMaxCount << "\n"; } } while (false);
397 LLVM_DEBUG(dbgs() << "Peel cost: " << LoopSize * (*PeelCount + 1)do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-unroll")) { dbgs() << "Peel cost: " << LoopSize
* (*PeelCount + 1) << "\n"; } } while (false)
398 << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-unroll")) { dbgs() << "Peel cost: " << LoopSize
* (*PeelCount + 1) << "\n"; } } while (false);
399 LLVM_DEBUG(dbgs() << "Max peel cost: " << UP.Threshold << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-unroll")) { dbgs() << "Max peel cost: " <<
UP.Threshold << "\n"; } } while (false);
400 }
401 }
402}
403
404/// Update the branch weights of the latch of a peeled-off loop
405/// iteration.
406/// This sets the branch weights for the latch of the recently peeled off loop
407/// iteration correctly.
408/// Let F is a weight of the edge from latch to header.
409/// Let E is a weight of the edge from latch to exit.
410/// F/(F+E) is a probability to go to loop and E/(F+E) is a probability to
411/// go to exit.
412/// Then, Estimated TripCount = F / E.
413/// For I-th (counting from 0) peeled off iteration we set the the weights for
414/// the peeled latch as (TC - I, 1). It gives us reasonable distribution,
415/// The probability to go to exit 1/(TC-I) increases. At the same time
416/// the estimated trip count of remaining loop reduces by I.
417/// To avoid dealing with division rounding we can just multiple both part
418/// of weights to E and use weight as (F - I * E, E).
419///
420/// \param Header The copy of the header block that belongs to next iteration.
421/// \param LatchBR The copy of the latch branch that belongs to this iteration.
422/// \param[in,out] FallThroughWeight The weight of the edge from latch to
423/// header before peeling (in) and after peeled off one iteration (out).
424static void updateBranchWeights(BasicBlock *Header, BranchInst *LatchBR,
425 uint64_t ExitWeight,
426 uint64_t &FallThroughWeight) {
427 // FallThroughWeight is 0 means that there is no branch weights on original
428 // latch block or estimated trip count is zero.
429 if (!FallThroughWeight)
430 return;
431
432 unsigned HeaderIdx = (LatchBR->getSuccessor(0) == Header ? 0 : 1);
433 MDBuilder MDB(LatchBR->getContext());
434 MDNode *WeightNode =
435 HeaderIdx ? MDB.createBranchWeights(ExitWeight, FallThroughWeight)
436 : MDB.createBranchWeights(FallThroughWeight, ExitWeight);
437 LatchBR->setMetadata(LLVMContext::MD_prof, WeightNode);
438 FallThroughWeight =
439 FallThroughWeight > ExitWeight ? FallThroughWeight - ExitWeight : 1;
440}
441
442/// Initialize the weights.
443///
444/// \param Header The header block.
445/// \param LatchBR The latch branch.
446/// \param[out] ExitWeight The weight of the edge from Latch to Exit.
447/// \param[out] FallThroughWeight The weight of the edge from Latch to Header.
448static void initBranchWeights(BasicBlock *Header, BranchInst *LatchBR,
449 uint64_t &ExitWeight,
450 uint64_t &FallThroughWeight) {
451 uint64_t TrueWeight, FalseWeight;
452 if (!LatchBR->extractProfMetadata(TrueWeight, FalseWeight))
453 return;
454 unsigned HeaderIdx = LatchBR->getSuccessor(0) == Header ? 0 : 1;
455 ExitWeight = HeaderIdx ? TrueWeight : FalseWeight;
456 FallThroughWeight = HeaderIdx ? FalseWeight : TrueWeight;
457}
458
459/// Update the weights of original Latch block after peeling off all iterations.
460///
461/// \param Header The header block.
462/// \param LatchBR The latch branch.
463/// \param ExitWeight The weight of the edge from Latch to Exit.
464/// \param FallThroughWeight The weight of the edge from Latch to Header.
465static void fixupBranchWeights(BasicBlock *Header, BranchInst *LatchBR,
466 uint64_t ExitWeight,
467 uint64_t FallThroughWeight) {
468 // FallThroughWeight is 0 means that there is no branch weights on original
469 // latch block or estimated trip count is zero.
470 if (!FallThroughWeight)
471 return;
472
473 // Sets the branch weights on the loop exit.
474 MDBuilder MDB(LatchBR->getContext());
475 unsigned HeaderIdx = LatchBR->getSuccessor(0) == Header ? 0 : 1;
476 MDNode *WeightNode =
477 HeaderIdx ? MDB.createBranchWeights(ExitWeight, FallThroughWeight)
478 : MDB.createBranchWeights(FallThroughWeight, ExitWeight);
479 LatchBR->setMetadata(LLVMContext::MD_prof, WeightNode);
480}
481
482/// Clones the body of the loop L, putting it between \p InsertTop and \p
483/// InsertBot.
484/// \param IterNumber The serial number of the iteration currently being
485/// peeled off.
486/// \param ExitEdges The exit edges of the original loop.
487/// \param[out] NewBlocks A list of the blocks in the newly created clone
488/// \param[out] VMap The value map between the loop and the new clone.
489/// \param LoopBlocks A helper for DFS-traversal of the loop.
490/// \param LVMap A value-map that maps instructions from the original loop to
491/// instructions in the last peeled-off iteration.
492static void cloneLoopBlocks(
493 Loop *L, unsigned IterNumber, BasicBlock *InsertTop, BasicBlock *InsertBot,
494 SmallVectorImpl<std::pair<BasicBlock *, BasicBlock *> > &ExitEdges,
495 SmallVectorImpl<BasicBlock *> &NewBlocks, LoopBlocksDFS &LoopBlocks,
496 ValueToValueMapTy &VMap, ValueToValueMapTy &LVMap, DominatorTree *DT,
497 LoopInfo *LI) {
498 BasicBlock *Header = L->getHeader();
499 BasicBlock *Latch = L->getLoopLatch();
500 BasicBlock *PreHeader = L->getLoopPreheader();
501
502 Function *F = Header->getParent();
503 LoopBlocksDFS::RPOIterator BlockBegin = LoopBlocks.beginRPO();
504 LoopBlocksDFS::RPOIterator BlockEnd = LoopBlocks.endRPO();
505 Loop *ParentLoop = L->getParentLoop();
506
507 // For each block in the original loop, create a new copy,
508 // and update the value map with the newly created values.
509 for (LoopBlocksDFS::RPOIterator BB = BlockBegin; BB != BlockEnd; ++BB) {
510 BasicBlock *NewBB = CloneBasicBlock(*BB, VMap, ".peel", F);
511 NewBlocks.push_back(NewBB);
512
513 // If an original block is an immediate child of the loop L, its copy
514 // is a child of a ParentLoop after peeling. If a block is a child of
515 // a nested loop, it is handled in the cloneLoop() call below.
516 if (ParentLoop && LI->getLoopFor(*BB) == L)
517 ParentLoop->addBasicBlockToLoop(NewBB, *LI);
518
519 VMap[*BB] = NewBB;
520
521 // If dominator tree is available, insert nodes to represent cloned blocks.
522 if (DT) {
523 if (Header == *BB)
524 DT->addNewBlock(NewBB, InsertTop);
525 else {
526 DomTreeNode *IDom = DT->getNode(*BB)->getIDom();
527 // VMap must contain entry for IDom, as the iteration order is RPO.
528 DT->addNewBlock(NewBB, cast<BasicBlock>(VMap[IDom->getBlock()]));
529 }
530 }
531 }
532
533 // Recursively create the new Loop objects for nested loops, if any,
534 // to preserve LoopInfo.
535 for (Loop *ChildLoop : *L) {
536 cloneLoop(ChildLoop, ParentLoop, VMap, LI, nullptr);
537 }
538
539 // Hook-up the control flow for the newly inserted blocks.
540 // The new header is hooked up directly to the "top", which is either
541 // the original loop preheader (for the first iteration) or the previous
542 // iteration's exiting block (for every other iteration)
543 InsertTop->getTerminator()->setSuccessor(0, cast<BasicBlock>(VMap[Header]));
544
545 // Similarly, for the latch:
546 // The original exiting edge is still hooked up to the loop exit.
547 // The backedge now goes to the "bottom", which is either the loop's real
548 // header (for the last peeled iteration) or the copied header of the next
549 // iteration (for every other iteration)
550 BasicBlock *NewLatch = cast<BasicBlock>(VMap[Latch]);
551 BranchInst *LatchBR = cast<BranchInst>(NewLatch->getTerminator());
552 for (unsigned idx = 0, e = LatchBR->getNumSuccessors(); idx < e; ++idx)
553 if (LatchBR->getSuccessor(idx) == Header) {
554 LatchBR->setSuccessor(idx, InsertBot);
555 break;
556 }
557 if (DT)
558 DT->changeImmediateDominator(InsertBot, NewLatch);
559
560 // The new copy of the loop body starts with a bunch of PHI nodes
561 // that pick an incoming value from either the preheader, or the previous
562 // loop iteration. Since this copy is no longer part of the loop, we
563 // resolve this statically:
564 // For the first iteration, we use the value from the preheader directly.
565 // For any other iteration, we replace the phi with the value generated by
566 // the immediately preceding clone of the loop body (which represents
567 // the previous iteration).
568 for (BasicBlock::iterator I = Header->begin(); isa<PHINode>(I); ++I) {
569 PHINode *NewPHI = cast<PHINode>(VMap[&*I]);
570 if (IterNumber == 0) {
571 VMap[&*I] = NewPHI->getIncomingValueForBlock(PreHeader);
572 } else {
573 Value *LatchVal = NewPHI->getIncomingValueForBlock(Latch);
574 Instruction *LatchInst = dyn_cast<Instruction>(LatchVal);
575 if (LatchInst && L->contains(LatchInst))
576 VMap[&*I] = LVMap[LatchInst];
577 else
578 VMap[&*I] = LatchVal;
579 }
580 cast<BasicBlock>(VMap[Header])->getInstList().erase(NewPHI);
581 }
582
583 // Fix up the outgoing values - we need to add a value for the iteration
584 // we've just created. Note that this must happen *after* the incoming
585 // values are adjusted, since the value going out of the latch may also be
586 // a value coming into the header.
587 for (auto Edge : ExitEdges)
588 for (PHINode &PHI : Edge.second->phis()) {
589 Value *LatchVal = PHI.getIncomingValueForBlock(Edge.first);
590 Instruction *LatchInst = dyn_cast<Instruction>(LatchVal);
591 if (LatchInst && L->contains(LatchInst))
592 LatchVal = VMap[LatchVal];
593 PHI.addIncoming(LatchVal, cast<BasicBlock>(VMap[Edge.first]));
594 }
595
596 // LastValueMap is updated with the values for the current loop
597 // which are used the next time this function is called.
598 for (auto KV : VMap)
599 LVMap[KV.first] = KV.second;
600}
601
602/// Peel off the first \p PeelCount iterations of loop \p L.
603///
604/// Note that this does not peel them off as a single straight-line block.
605/// Rather, each iteration is peeled off separately, and needs to check the
606/// exit condition.
607/// For loops that dynamically execute \p PeelCount iterations or less
608/// this provides a benefit, since the peeled off iterations, which account
609/// for the bulk of dynamic execution, can be further simplified by scalar
610/// optimizations.
611bool llvm::peelLoop(Loop *L, unsigned PeelCount, LoopInfo *LI,
612 ScalarEvolution *SE, DominatorTree *DT,
613 AssumptionCache *AC, bool PreserveLCSSA) {
614 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-11~++20200309111110+2c36c23f347/llvm/lib/Transforms/Utils/LoopUnrollPeel.cpp"
, 614, __PRETTY_FUNCTION__));
1
Assuming 'PeelCount' is > 0
→
2
←
'?' condition is true
→
615 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-11~++20200309111110+2c36c23f347/llvm/lib/Transforms/Utils/LoopUnrollPeel.cpp"
, 615, __PRETTY_FUNCTION__));
3
←
'?' condition is true
→
616
617 LoopBlocksDFS LoopBlocks(L);
618 LoopBlocks.perform(LI);
619
620 BasicBlock *Header = L->getHeader();
621 BasicBlock *PreHeader = L->getLoopPreheader();
622 BasicBlock *Latch = L->getLoopLatch();
623 SmallVector<std::pair<BasicBlock *, BasicBlock *>, 4> ExitEdges;
624 L->getExitEdges(ExitEdges);
625
626 DenseMap<BasicBlock *, BasicBlock *> ExitIDom;
627 if (DT) {
4
←
Assuming 'DT' is null
→
5
←
Taking false branch
→
628 // We'd like to determine the idom of exit block after peeling one
629 // iteration.
630 // Let Exit is exit block.
631 // Let ExitingSet - is a set of predecessors of Exit block. They are exiting
632 // blocks.
633 // Let Latch' and ExitingSet' are copies after a peeling.
634 // We'd like to find an idom'(Exit) - idom of Exit after peeling.
635 // It is an evident that idom'(Exit) will be the nearest common dominator
636 // of ExitingSet and ExitingSet'.
637 // idom(Exit) is a nearest common dominator of ExitingSet.
638 // idom(Exit)' is a nearest common dominator of ExitingSet'.
639 // Taking into account that we have a single Latch, Latch' will dominate
640 // Header and idom(Exit).
641 // So the idom'(Exit) is nearest common dominator of idom(Exit)' and Latch'.
642 // All these basic blocks are in the same loop, so what we find is
643 // (nearest common dominator of idom(Exit) and Latch)'.
644 // In the loop below we remember nearest common dominator of idom(Exit) and
645 // Latch to update idom of Exit later.
646 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-11~++20200309111110+2c36c23f347/llvm/lib/Transforms/Utils/LoopUnrollPeel.cpp"
, 646, __PRETTY_FUNCTION__));
647 for (auto Edge : ExitEdges) {
648 if (ExitIDom.count(Edge.second))
649 continue;
650 BasicBlock *BB = DT->findNearestCommonDominator(
651 DT->getNode(Edge.second)->getIDom()->getBlock(), Latch);
652 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-11~++20200309111110+2c36c23f347/llvm/lib/Transforms/Utils/LoopUnrollPeel.cpp"
, 652, __PRETTY_FUNCTION__));
653 ExitIDom[Edge.second] = BB;
654 }
655 }
656
657 Function *F = Header->getParent();
658
659 // Set up all the necessary basic blocks. It is convenient to split the
660 // preheader into 3 parts - two blocks to anchor the peeled copy of the loop
661 // body, and a new preheader for the "real" loop.
662
663 // Peeling the first iteration transforms.
664 //
665 // PreHeader:
666 // ...
667 // Header:
668 // LoopBody
669 // If (cond) goto Header
670 // Exit:
671 //
672 // into
673 //
674 // InsertTop:
675 // LoopBody
676 // If (!cond) goto Exit
677 // InsertBot:
678 // NewPreHeader:
679 // ...
680 // Header:
681 // LoopBody
682 // If (cond) goto Header
683 // Exit:
684 //
685 // Each following iteration will split the current bottom anchor in two,
686 // and put the new copy of the loop body between these two blocks. That is,
687 // after peeling another iteration from the example above, we'll split
688 // InsertBot, and get:
689 //
690 // InsertTop:
691 // LoopBody
692 // If (!cond) goto Exit
693 // InsertBot:
694 // LoopBody
695 // If (!cond) goto Exit
696 // InsertBot.next:
697 // NewPreHeader:
698 // ...
699 // Header:
700 // LoopBody
701 // If (cond) goto Header
702 // Exit:
703
704 BasicBlock *InsertTop = SplitEdge(PreHeader, Header, DT, LI);
705 BasicBlock *InsertBot =
706 SplitBlock(InsertTop, InsertTop->getTerminator(), DT, LI);
707 BasicBlock *NewPreHeader =
708 SplitBlock(InsertBot, InsertBot->getTerminator(), DT, LI);
709
710 InsertTop->setName(Header->getName() + ".peel.begin");
711 InsertBot->setName(Header->getName() + ".peel.next");
712 NewPreHeader->setName(PreHeader->getName() + ".peel.newph");
713
714 ValueToValueMapTy LVMap;
715
716 // If we have branch weight information, we'll want to update it for the
717 // newly created branches.
718 BranchInst *LatchBR =
719 cast<BranchInst>(cast<BasicBlock>(Latch)->getTerminator());
6
←
'Latch' is a 'BasicBlock'
→
7
←
The object is a 'BranchInst'
→
720 uint64_t ExitWeight = 0, FallThroughWeight = 0;
721 initBranchWeights(Header, LatchBR, ExitWeight, FallThroughWeight);
722
723 // For each peeled-off iteration, make a copy of the loop.
724 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 765
→
725 SmallVector<BasicBlock *, 8> NewBlocks;
726 ValueToValueMapTy VMap;
727
728 cloneLoopBlocks(L, Iter, InsertTop, InsertBot, ExitEdges, NewBlocks,
729 LoopBlocks, VMap, LVMap, DT, LI);
730
731 // Remap to use values from the current iteration instead of the
732 // previous one.
733 remapInstructionsInBlocks(NewBlocks, VMap);
734
735 if (DT
8.1
'DT' is null
) {
9
←
Taking false branch
→
736 // Latches of the cloned loops dominate over the loop exit, so idom of the
737 // latter is the first cloned loop body, as original PreHeader dominates
738 // the original loop body.
739 if (Iter == 0)
740 for (auto Exit : ExitIDom)
741 DT->changeImmediateDominator(Exit.first,
742 cast<BasicBlock>(LVMap[Exit.second]));
743#ifdef EXPENSIVE_CHECKS
744 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-11~++20200309111110+2c36c23f347/llvm/lib/Transforms/Utils/LoopUnrollPeel.cpp"
, 744, __PRETTY_FUNCTION__));
745#endif
746 }
747
748 auto *LatchBRCopy = cast<BranchInst>(VMap[LatchBR]);
749 updateBranchWeights(InsertBot, LatchBRCopy, ExitWeight, FallThroughWeight);
750 // Remove Loop metadata from the latch branch instruction
751 // because it is not the Loop's latch branch anymore.
752 LatchBRCopy->setMetadata(LLVMContext::MD_loop, nullptr);
753
754 InsertTop = InsertBot;
755 InsertBot = SplitBlock(InsertBot, InsertBot->getTerminator(), DT, LI);
756 InsertBot->setName(Header->getName() + ".peel.next");
757
758 F->getBasicBlockList().splice(InsertTop->getIterator(),
759 F->getBasicBlockList(),
760 NewBlocks[0]->getIterator(), F->end());
761 }
762
763 // Now adjust the phi nodes in the loop header to get their initial values
764 // from the last peeled-off iteration instead of the preheader.
765 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 775
→
766 PHINode *PHI = cast<PHINode>(I);
767 Value *NewVal = PHI->getIncomingValueForBlock(Latch);
768 Instruction *LatchInst = dyn_cast<Instruction>(NewVal);
769 if (LatchInst && L->contains(LatchInst))
770 NewVal = LVMap[LatchInst];
771
772 PHI->setIncomingValueForBlock(NewPreHeader, NewVal);
773 }
774
775 fixupBranchWeights(Header, LatchBR, ExitWeight, FallThroughWeight);
776
777 // Update Metadata for count of peeled off iterations.
778 unsigned AlreadyPeeled = 0;
779 if (auto Peeled = getOptionalIntLoopAttribute(L, PeeledCountMetaData))
14
←
Assuming the condition is false
→
15
←
Taking false branch
→
780 AlreadyPeeled = *Peeled;
781 addStringMetadataToLoop(L, PeeledCountMetaData, AlreadyPeeled + PeelCount);
782
783 if (Loop *ParentLoop = L->getParentLoop())
16
←
Assuming 'ParentLoop' is null
→
17
←
Taking false branch
→
784 L = ParentLoop;
785
786 // We modified the loop, update SE.
787 SE->forgetTopmostLoop(L);
788
789 // Finally DomtTree must be correct.
790 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-11~++20200309111110+2c36c23f347/llvm/lib/Transforms/Utils/LoopUnrollPeel.cpp"
, 790, __PRETTY_FUNCTION__));
18
←
Called C++ object pointer is null
791
792 // FIXME: Incrementally update loop-simplify
793 simplifyLoop(L, DT, LI, SE, AC, nullptr, PreserveLCSSA);
794
795 NumPeeled++;
796
797 return true;
798}