instcombine: alloca: Canonicalize scalar allocation array size

As a follow-up to r232200, add an `-instcombine` to canonicalize scalar
allocations to `i32 1`.  Since r232200, `iX 1` (for X != 32) are only
created by RAUWs, so this shouldn't fire too often.  Nevertheless, it's
a cheap check and a nice cleanup.

llvm-svn: 232202

1 files changed, 10 insertions, 2 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp b/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
index deed58c425e..73dd40e4d19 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
@@ -166,8 +166,16 @@ isOnlyCopiedFromConstantGlobal(AllocaInst *AI,
 
 static Instruction *simplifyAllocaArraySize(InstCombiner &IC, AllocaInst &AI) {
   // Check for array size of 1 (scalar allocation).
-  if (!AI.isArrayAllocation())
-    return nullptr;
+  if (!AI.isArrayAllocation()) {
+    // i32 1 is the canonical array size for scalar allocations.
+    if (AI.getArraySize()->getType()->isIntegerTy(32))
+      return nullptr;
+
+    // Canonicalize it.
+    Value *V = IC.Builder->getInt32(1);
+    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())) {