instcombine: alloca: Limit array size type promotion

Move type promotion of the size of the array allocation to the end of
`simplifyAllocaArraySize()`.  This avoids promoting the type of the
array size if it's a `ConstantInt`, since the next -instcombine
iteration will drop it to a scalar allocation anyway.  Similarly, this
avoids promoting the type if it's an `UndefValue`, in which case the
alloca gets RAUW'ed.

This is NFC when considered over the lifetime of -instcombine, since
it's just reducing the number of iterations needed to reach fixed point.

llvm-svn: 232201

1 files changed, 9 insertions, 9 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp b/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
index a44a8deda1a..deed58c425e 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
@@ -169,15 +169,6 @@ static Instruction *simplifyAllocaArraySize(InstCombiner &IC, AllocaInst &AI) {
   if (!AI.isArrayAllocation())
     return nullptr;
 
-  // Ensure that the alloca array size argument has type intptr_t, so that
-  // any casting is exposed early.
-  Type *IntPtrTy = IC.getDataLayout().getIntPtrType(AI.getType());
-  if (AI.getArraySize()->getType() != IntPtrTy) {
-    Value *V = IC.Builder->CreateIntCast(AI.getArraySize(), IntPtrTy, false);
-    AI.setOperand(0, V);
-    return &AI;
-  }
-
   // Convert: alloca Ty, C - where C is a constant != 1 into: alloca [C x Ty], 1
   if (const ConstantInt *C = dyn_cast<ConstantInt>(AI.getArraySize())) {
     Type *NewTy = ArrayType::get(AI.getAllocatedType(), C->getZExtValue());
@@ -209,6 +200,15 @@ static Instruction *simplifyAllocaArraySize(InstCombiner &IC, AllocaInst &AI) {
   if (isa<UndefValue>(AI.getArraySize()))
     return IC.ReplaceInstUsesWith(AI, Constant::getNullValue(AI.getType()));
 
+  // Ensure that the alloca array size argument has type intptr_t, so that
+  // any casting is exposed early.
+  Type *IntPtrTy = IC.getDataLayout().getIntPtrType(AI.getType());
+  if (AI.getArraySize()->getType() != IntPtrTy) {
+    Value *V = IC.Builder->CreateIntCast(AI.getArraySize(), IntPtrTy, false);
+    AI.setOperand(0, V);
+    return &AI;
+  }
+
   return nullptr;
 }