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[LoopFusion] Bails out if only the second candidate is guarded (PR48060) 

If only the second candidate loop is guarded while the first one is not, fusioning
two loops might not be valid but this check is currently missing.

Fixes https://bugs.llvm.org/show_bug.cgi?id=48060

Reviewed By: sidbav

Differential Revision: https://reviews.llvm.org/D99716
This commit is contained in:
Ta-Wei Tu 2021-04-06 01:08:35 +08:00
parent df64f471d1
commit 6a82ace5f2
2 changed files with 79 additions and 0 deletions
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10
llvm/lib/Transforms/Scalar/LoopFuse.cpp
View File

@ -99,6 +99,8 @@ STATISTIC(NonEmptyExitBlock, "Candidate has a non-empty exit block with "
STATISTIC(NonEmptyGuardBlock, "Candidate has a non-empty guard block with "
"instructions that cannot be moved");
STATISTIC(NotRotated, "Candidate is not rotated");
STATISTIC(OnlySecondCandidateIsGuarded,
"The second candidate is guarded while the first one is not");
enum FusionDependenceAnalysisChoice {
FUSION_DEPENDENCE_ANALYSIS_SCEV,
@ -891,6 +893,14 @@ private:
continue;
}
if (!FC0->GuardBranch && FC1->GuardBranch) {
LLVM_DEBUG(dbgs() << "The second candidate is guarded while the "
"first one is not. Not fusing.\n");
reportLoopFusion<OptimizationRemarkMissed>(
*FC0, *FC1, OnlySecondCandidateIsGuarded);
continue;
}
// Ensure that FC0 and FC1 have identical guards.
// If one (or both) are not guarded, this check is not necessary.
if (FC0->GuardBranch && FC1->GuardBranch &&

69
llvm/test/Transforms/LoopFusion/pr48060.ll Normal file
View File

@ -0,0 +1,69 @@
; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
; RUN: opt -S -loop-fusion < %s | FileCheck %s
; RUN: opt -S -loop-fusion -pass-remarks-output=%t < %s
; RUN: FileCheck --input-file=%t %s --check-prefix REMARKS
define dso_local void @pr48060(i1 %cond) {
; CHECK-LABEL: @pr48060(
; CHECK-NEXT: entry:
; CHECK-NEXT: br label [[FOR_1_PH:%.*]]
; CHECK: for.1.ph:
; CHECK-NEXT: br label [[FOR_1:%.*]]
; CHECK: for.1:
; CHECK-NEXT: [[I:%.*]] = phi i32 [ 0, [[FOR_1_PH]] ], [ [[I_NEXT:%.*]], [[FOR_1]] ]
; CHECK-NEXT: [[I_NEXT]] = add i32 [[I]], 1
; CHECK-NEXT: [[COND_1:%.*]] = icmp eq i32 [[I_NEXT]], 10
; CHECK-NEXT: br i1 [[COND_1]], label [[FOR_1_EXIT:%.*]], label [[FOR_1]]
; CHECK: for.1.exit:
; CHECK-NEXT: br i1 [[COND:%.*]], label [[END:%.*]], label [[FOR_2_PH:%.*]]
; CHECK: for.2.ph:
; CHECK-NEXT: br label [[FOR_2:%.*]]
; CHECK: for.2:
; CHECK-NEXT: [[J:%.*]] = phi i32 [ 0, [[FOR_2_PH]] ], [ [[J_NEXT:%.*]], [[FOR_2]] ]
; CHECK-NEXT: [[J_NEXT]] = add i32 [[J]], 1
; CHECK-NEXT: [[COND_2:%.*]] = icmp eq i32 [[J_NEXT]], 10
; CHECK-NEXT: br i1 [[COND_2]], label [[FOR_2_EXIT:%.*]], label [[FOR_2]]
; CHECK: for.2.exit:
; CHECK-NEXT: br label [[END]]
; CHECK: end:
; CHECK-NEXT: ret void
;
; REMARKS: --- !Missed
; REMARKS-NEXT: Pass: loop-fusion
; REMARKS-NEXT: Name: OnlySecondCandidateIsGuarded
; REMARKS-NEXT: Function: pr48060
; REMARKS-NEXT: Args:
; REMARKS: - Cand1: for.1.ph
; REMARKS: - Cand2: for.2.ph
; REMARKS: - String: The second candidate is guarded while the first one is not
entry:
br label %for.1.ph
for.1.ph: ; preds = %entry
br label %for.1
for.1: ; preds = %for.1, %for.1.ph
%i = phi i32 [ 0, %for.1.ph ], [ %i.next, %for.1 ]
%i.next = add i32 %i, 1
%cond.1 = icmp eq i32 %i.next, 10
br i1 %cond.1, label %for.1.exit, label %for.1
for.1.exit: ; preds = %for.1
br i1 %cond, label %end, label %for.2.ph
for.2.ph: ; preds = %for.1.exit
br label %for.2
for.2: ; preds = %for.2, %for.2.ph
%j = phi i32 [ 0, %for.2.ph ], [ %j.next, %for.2 ]
%j.next = add i32 %j, 1
%cond.2 = icmp eq i32 %j.next, 10
br i1 %cond.2, label %for.2.exit, label %for.2
for.2.exit: ; preds = %for.2
br label %end
end: ; preds = %for.1.exit, %for.2.exit
ret void
}