[SimplifyCFG] Don't create PHI nodes for constant bundle operands

Summary:
Constant bundle operands may need to retain their constant-ness for
correctness.  I'll admit that this is slightly odd, but it looks like
SimplifyCFG already does this for things like @llvm.frameaddress and
@llvm.stackmap, so I suppose adding one more case is not a big deal.

It is possible to add a mechanism to denote bundle operands that need to
remain constants, but that's probably too complicated for the time
being.

Reviewers: jmolloy

Subscribers: mcrosier, llvm-commits

Differential Revision: https://reviews.llvm.org/D25502

llvm-svn: 284028

1 files changed, 10 insertions, 1 deletions

diff --git a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
index 63b9f4061f2..a45a0c75b46 100644
--- a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -1362,7 +1362,16 @@ static bool canReplaceOperandWithVariable(const Instruction *I,
     // FIXME: many arithmetic intrinsics have no issue taking a
     // variable, however it's hard to distingish these from
     // specials such as @llvm.frameaddress that require a constant.
-    return !isa<IntrinsicInst>(I);
+    if (isa<IntrinsicInst>(I))
+      return false;
+
+    // Constant bundle operands may need to retain their constant-ness for
+    // correctness.
+    if (ImmutableCallSite(I).isBundleOperand(OpIdx))
+      return false;
+
+    return true;
+
   case Instruction::ShuffleVector:
     // Shufflevector masks are constant.
     return OpIdx != 2;