[llvm] r197791 - Transforms: Don't create bad weights when eliminating dead cases

[Justin Bogner]

Author: bogner
Date: Fri Dec 20 02:21:30 2013
New Revision: 197791

URL: http://llvm.org/viewvc/llvm-project?rev=197791&view=rev
Log:
Transforms: Don't create bad weights when eliminating dead cases

If we happen to eliminate every case in a switch that has branch
weights, we currently try to create metadata for the one remaining
branch, triggering an assert. Instead, we need to check that the
metadata we're trying to create is sensible.

Modified:
    llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp
    llvm/trunk/test/Transforms/SimplifyCFG/preserve-branchweights.ll

Modified: llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp?rev=197791&r1=197790&r2=197791&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp (original)
+++ llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp Fri Dec 20 02:21:30 2013
@@ -3222,7 +3222,7 @@ static bool EliminateDeadSwitchCases(Swi
     Case.getCaseSuccessor()->removePredecessor(SI->getParent());
     SI->removeCase(Case);
   }
-  if (HasWeight) {
+  if (HasWeight && Weights.size() >= 2) {
     SmallVector<uint32_t, 8> MDWeights(Weights.begin(), Weights.end());
     SI->setMetadata(LLVMContext::MD_prof,
                     MDBuilder(SI->getParent()->getContext()).

Modified: llvm/trunk/test/Transforms/SimplifyCFG/preserve-branchweights.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/SimplifyCFG/preserve-branchweights.ll?rev=197791&r1=197790&r2=197791&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/SimplifyCFG/preserve-branchweights.ll (original)
+++ llvm/trunk/test/Transforms/SimplifyCFG/preserve-branchweights.ll Fri Dec 20 02:21:30 2013
@@ -313,6 +313,31 @@ sw.epilog:
   ret void
 }
 
+;; If every case is dead, make sure they are all removed. This used to
+;; crash trying to merge the metadata.
+define void @test13(i32 %x) nounwind {
+entry:
+  %i = shl i32 %x, 1
+  switch i32 %i, label %a [
+    i32 21, label %b
+    i32 25, label %c
+  ], !prof !8
+; CHECK-LABEL: @test13(
+; CHECK-NEXT: entry:
+; CHECK-NEXT: call void @helper
+; CHECK-NEXT: ret void
+
+a:
+ call void @helper(i32 0) nounwind
+ ret void
+b:
+ call void @helper(i32 1) nounwind
+ ret void
+c:
+ call void @helper(i32 2) nounwind
+ ret void
+}
+
 !0 = metadata !{metadata !"branch_weights", i32 3, i32 5}
 !1 = metadata !{metadata !"branch_weights", i32 1, i32 1}
 !2 = metadata !{metadata !"branch_weights", i32 1, i32 2}