Modify constraints in `llvm::canReplaceOperandWithVariable`

Summary:
`Instruction::Switch`: only first operand can be set to a non-constant value.
`Instruction::InsertValue` both the first and the second operand can be set to a non-constant value.
`Instruction::Alloca` return true for non-static allocation.

Reviewers: efriedma

Reviewed By: efriedma

Subscribers: srhines, pirama, llvm-commits

Differential Revision: https://reviews.llvm.org/D34905

llvm-svn: 307294

1 files changed, 8 insertions, 2 deletions

diff --git a/llvm/lib/Transforms/Utils/Local.cpp b/llvm/lib/Transforms/Utils/Local.cpp
index 5127eba..e4c94ac 100644
--- a/llvm/lib/Transforms/Utils/Local.cpp
+++ b/llvm/lib/Transforms/Utils/Local.cpp
@@ -2182,12 +2182,18 @@ bool llvm::canReplaceOperandWithVariable(const Instruction *I, unsigned OpIdx) {
   case Instruction::ShuffleVector:
     // Shufflevector masks are constant.
     return OpIdx != 2;
+  case Instruction::Switch:
   case Instruction::ExtractValue:
-  case Instruction::InsertValue:
     // All operands apart from the first are constant.
     return OpIdx == 0;
+  case Instruction::InsertValue:
+    // All operands apart from the first and the second are constant.
+    return OpIdx < 2;
   case Instruction::Alloca:
-    return false;
+    // Static allocas (constant size in the entry block) are handled by
+    // prologue/epilogue insertion so they're free anyway. We definitely don't
+    // want to make them non-constant.
+    return !dyn_cast<AllocaInst>(I)->isStaticAlloca();
   case Instruction::GetElementPtr:
     if (OpIdx == 0)
       return true;