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[PGO][CHR] Guard against 0-to-0 branch weight and avoid division by zero crash. 

Summary: This fixes a crash in internal builds under SamplePGO.

Reviewers: davidxl

Subscribers: hiraditya, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D72653
This commit is contained in:
Hiroshi Yamauchi 2020-01-13 14:19:45 -08:00
parent a506f7f910
commit 7b9f8e17d1
2 changed files with 30 additions and 0 deletions
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4
llvm/lib/Transforms/Instrumentation/ControlHeightReduction.cpp
View File

@ -625,6 +625,10 @@ static bool checkMDProf(MDNode *MD, BranchProbability &TrueProb,
assert(SumWt >= TrueWt && SumWt >= FalseWt &&
"Overflow calculating branch probabilities.");
// Guard against 0-to-0 branch weights to avoid a division-by-zero crash.
if (SumWt == 0)
return false;
TrueProb = BranchProbability::getBranchProbability(TrueWt, SumWt);
FalseProb = BranchProbability::getBranchProbability(FalseWt, SumWt);
return true;

26
llvm/test/Transforms/PGOProfile/chr.ll
View File

@ -2463,6 +2463,31 @@ end:
ret i64 99
}
; Test to not crash upon a 0:0 branch_weight metadata.
define void @test_chr_24(i32* %i) !prof !14 {
entry:
%0 = load i32, i32* %i
%1 = and i32 %0, 1
%2 = icmp eq i32 %1, 0
br i1 %2, label %bb1, label %bb0, !prof !17
bb0:
call void @foo()
br label %bb1
bb1:
%3 = and i32 %0, 2
%4 = icmp eq i32 %3, 0
br i1 %4, label %bb3, label %bb2, !prof !17
bb2:
call void @foo()
br label %bb3
bb3:
ret void
}
!llvm.module.flags = !{!0}
!0 = !{i32 1, !"ProfileSummary", !1}
!1 = !{!2, !3, !4, !5, !6, !7, !8, !9}
@ -2482,6 +2507,7 @@ end:
!14 = !{!"function_entry_count", i64 100}
!15 = !{!"branch_weights", i32 0, i32 1}
!16 = !{!"branch_weights", i32 1, i32 1}
!17 = !{!"branch_weights", i32 0, i32 0}
; CHECK: !15 = !{!"branch_weights", i32 1000, i32 0}
; CHECK: !16 = !{!"branch_weights", i32 0, i32 1}
; CHECK: !17 = !{!"branch_weights", i32 1, i32 1}