[PATCH] D81449: [JumpThreading] Handle zero !prof branch_weights

[Yevgeny Rouban via Phabricator via llvm-commits]

yrouban created this revision.
yrouban added reviewers: kazu, nikic, yamauchi, ebrevnov, efriedma.
Herald added a subscriber: hiraditya.
Herald added a project: LLVM.

Avoid division by zero in //updatePredecessorProfileMetadata()//. 
A test is added.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D81449

Files:
  llvm/lib/Transforms/Scalar/JumpThreading.cpp
  llvm/test/Transforms/JumpThreading/threading_prof3.ll


Index: llvm/test/Transforms/JumpThreading/threading_prof3.ll
===================================================================
--- /dev/null
+++ llvm/test/Transforms/JumpThreading/threading_prof3.ll
@@ -0,0 +1,30 @@
+; RUN: opt -jump-threading -S < %s | FileCheck %s
+; RUN: opt -passes=jump-threading -S < %s | FileCheck %s
+
+; Check that all zero branch weights do not cause a crash.
+define void @zero_branch_weights(i32 %tmp, i32 %tmp3) {
+bb:
+  %tmp1 = icmp eq i32 %tmp, 1
+  br i1 %tmp1, label %bb5, label %bb2
+; CHECK-NOT: br i1 %tmp1,{{.*}} !prof
+
+bb2:                                              
+  %tmp4 = icmp ne i32 %tmp3, 1
+  br label %bb5
+; CHECK: br i1 %tmp4, {{.*}} !prof ![[PROF:[0-9]+]]
+
+bb5:                                             
+  %tmp6 = phi i1 [ false, %bb ], [ %tmp4, %bb2 ]
+  br i1 %tmp6, label %bb8, label %bb7, !prof !{!"branch_weights", i32 0, i32 0}
+
+bb7:                                            
+  br label %bb9
+
+bb8: 
+  br label %bb9
+
+bb9:                                           
+  ret void
+}
+
+;CHECK: ![[PROF]] = !{!"branch_weights", i32 0, i32 0}
Index: llvm/lib/Transforms/Scalar/JumpThreading.cpp
===================================================================
--- llvm/lib/Transforms/Scalar/JumpThreading.cpp
+++ llvm/lib/Transforms/Scalar/JumpThreading.cpp
@@ -216,7 +216,8 @@
 
   BranchProbability BP;
   uint64_t TrueWeight, FalseWeight;
-  if (!CondBr->extractProfMetadata(TrueWeight, FalseWeight))
+  if (!CondBr->extractProfMetadata(TrueWeight, FalseWeight) ||
+      TrueWeight + FalseWeight == 0)
     return;
 
   // Returns the outgoing edge of the dominating predecessor block


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