[llvm] r232201 - instcombine: alloca: Limit array size type promotion

[Duncan P. N. Exon Smith]

Author: dexonsmith
Date: Fri Mar 13 14:34:55 2015
New Revision: 232201

URL: http://llvm.org/viewvc/llvm-project?rev=232201&view=rev
Log:
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.

Modified:
    llvm/trunk/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp

Modified: llvm/trunk/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp?rev=232201&r1=232200&r2=232201&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp (original)
+++ llvm/trunk/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp Fri Mar 13 14:34:55 2015
@@ -169,15 +169,6 @@ static Instruction *simplifyAllocaArrayS
   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 *simplifyAllocaArrayS
   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;
 }