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.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@197791 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Transforms/Utils/SimplifyCFG.cpp b/lib/Transforms/Utils/SimplifyCFG.cpp
index ff50b12cdb3fb62b743fd82364de9869c5237f92..0a45897961535a8994e95cb0963c542e4eb27b76 100644 (file)
--- a/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -3222,7 +3222,7 @@ static bool EliminateDeadSwitchCases(SwitchInst *SI) {
     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()).

diff --git a/test/Transforms/SimplifyCFG/preserve-branchweights.ll b/test/Transforms/SimplifyCFG/preserve-branchweights.ll
index 3c0bfebbd5649eb293a871ff4631dbbe6aff3f74..67f5636573d4519552f70bd1b7f8fc35f624471e 100644 (file)
--- a/test/Transforms/SimplifyCFG/preserve-branchweights.ll
+++ b/test/Transforms/SimplifyCFG/preserve-branchweights.ll
@@ -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}