[llvm] 7b9f8e1 - [PGO][CHR] Guard against 0-to-0 branch weight and avoid division by zero crash.

[Hiroshi Yamauchi via llvm-commits]

Author: Hiroshi Yamauchi
Date: 2020-01-13T14:38:58-08:00
New Revision: 7b9f8e17d15d7516b186c0a85de71133b780f939

URL: https://github.com/llvm/llvm-project/commit/7b9f8e17d15d7516b186c0a85de71133b780f939
DIFF: https://github.com/llvm/llvm-project/commit/7b9f8e17d15d7516b186c0a85de71133b780f939.diff

LOG: [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

Added: 
    

Modified: 
    llvm/lib/Transforms/Instrumentation/ControlHeightReduction.cpp
    llvm/test/Transforms/PGOProfile/chr.ll

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Transforms/Instrumentation/ControlHeightReduction.cpp b/llvm/lib/Transforms/Instrumentation/ControlHeightReduction.cpp
index 9bd1596852dd..d35abb92dd08 100644
--- a/llvm/lib/Transforms/Instrumentation/ControlHeightReduction.cpp
+++ b/llvm/lib/Transforms/Instrumentation/ControlHeightReduction.cpp
@@ -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;

diff  --git a/llvm/test/Transforms/PGOProfile/chr.ll b/llvm/test/Transforms/PGOProfile/chr.ll
index 0221a4fd000c..021ec2533501 100644
--- a/llvm/test/Transforms/PGOProfile/chr.ll
+++ b/llvm/test/Transforms/PGOProfile/chr.ll
@@ -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}