[llvm] r268935 - [CGP] avoid crashing from weightlessness

[Sanjay Patel via llvm-commits]

Author: spatel
Date: Mon May  9 12:31:55 2016
New Revision: 268935

URL: http://llvm.org/viewvc/llvm-project?rev=268935&view=rev
Log:
[CGP] avoid crashing from weightlessness

It's possible that we have branch weights with 0 values.
In that case, don't try to create an impossible BranchProbability.


Modified:
    llvm/trunk/lib/CodeGen/CodeGenPrepare.cpp
    llvm/trunk/test/CodeGen/X86/cmov-into-branch.ll

Modified: llvm/trunk/lib/CodeGen/CodeGenPrepare.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/CodeGenPrepare.cpp?rev=268935&r1=268934&r2=268935&view=diff
==============================================================================
--- llvm/trunk/lib/CodeGen/CodeGenPrepare.cpp (original)
+++ llvm/trunk/lib/CodeGen/CodeGenPrepare.cpp Mon May  9 12:31:55 2016
@@ -4559,9 +4559,11 @@ static bool isFormingBranchFromSelectPro
   if (SI->extractProfMetadata(TrueWeight, FalseWeight)) {
     uint64_t Max = std::max(TrueWeight, FalseWeight);
     uint64_t Sum = TrueWeight + FalseWeight;
-    auto Probability = BranchProbability::getBranchProbability(Max, Sum);
-    if (Probability > TLI->getPredictableBranchThreshold())
-      return true;
+    if (Sum != 0) {
+      auto Probability = BranchProbability::getBranchProbability(Max, Sum);
+      if (Probability > TLI->getPredictableBranchThreshold())
+        return true;
+    }
   }
 
   CmpInst *Cmp = dyn_cast<CmpInst>(SI->getCondition());

Modified: llvm/trunk/test/CodeGen/X86/cmov-into-branch.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/X86/cmov-into-branch.ll?rev=268935&r1=268934&r2=268935&view=diff
==============================================================================
--- llvm/trunk/test/CodeGen/X86/cmov-into-branch.ll (original)
+++ llvm/trunk/test/CodeGen/X86/cmov-into-branch.ll Mon May  9 12:31:55 2016
@@ -114,8 +114,22 @@ define i32 @weighted_select3(i32 %a, i32
   ret i32 %sel
 }
 
+; Weightlessness is no reason to die.
+define i32 @unweighted_select(i32 %a, i32 %b) {
+; CHECK-LABEL: unweighted_select:
+; CHECK:       # BB#0:
+; CHECK-NEXT:    testl %edi, %edi
+; CHECK-NEXT:    cmovnel %edi, %esi
+; CHECK-NEXT:    movl %esi, %eax
+; CHECK-NEXT:    retq
+;
+  %cmp = icmp ne i32 %a, 0
+  %sel = select i1 %cmp, i32 %a, i32 %b, !prof !3
+  ret i32 %sel
+}
 
 !0 = !{!"branch_weights", i32 1, i32 99}
 !1 = !{!"branch_weights", i32 1, i32 100}
 !2 = !{!"branch_weights", i32 100, i32 1}
+!3 = !{!"branch_weights", i32 0, i32 0}