Teach instcombine to promote alloca array sizes.

llvm-svn: 104945

2 files changed, 29 insertions, 3 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp b/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
index 0f2a24f59bd..fd3d5347028 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
@@ -22,6 +22,18 @@ using namespace llvm;
 STATISTIC(NumDeadStore, "Number of dead stores eliminated");
 
 Instruction *InstCombiner::visitAllocaInst(AllocaInst &AI) {
+  // Ensure that the alloca array size argument has type intptr_t, so that
+  // any casting is exposed early.
+  if (TD) {
+    const Type *IntPtrTy = TD->getIntPtrType(AI.getContext());
+    if (AI.getArraySize()->getType() != IntPtrTy) {
+      Value *V = 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 (AI.isArrayAllocation()) {  // Check C != 1
     if (const ConstantInt *C = dyn_cast<ConstantInt>(AI.getArraySize())) {
diff --git a/llvm/test/Transforms/InstCombine/alloca.ll b/llvm/test/Transforms/InstCombine/alloca.ll
index b9add4d7c21..e4d13673454 100644
--- a/llvm/test/Transforms/InstCombine/alloca.ll
+++ b/llvm/test/Transforms/InstCombine/alloca.ll
@@ -1,12 +1,13 @@
-; Zero byte allocas should be deleted.
 target datalayout = "E-p:64:64:64-a0:0:8-f32:32:32-f64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:32:64-v64:64:64-v128:128:128"
 
-; RUN: opt < %s -instcombine -S | \
-; RUN:   not grep alloca
+; RUN: opt < %s -instcombine -S | FileCheck %s
 ; END.
 
 declare void @use(...)
 
+; Zero byte allocas should be deleted.
+; CHECK: @test
+; CHECK-NOT: alloca
 define void @test() {
         %X = alloca [0 x i32]           ; <[0 x i32]*> [#uses=1]
         call void (...)* @use( [0 x i32]* %X )
@@ -17,12 +18,18 @@ define void @test() {
         ret void
 }
 
+; Zero byte allocas should be deleted.
+; CHECK: @test2
+; CHECK-NOT: alloca
 define void @test2() {
         %A = alloca i32         ; <i32*> [#uses=1]
         store i32 123, i32* %A
         ret void
 }
 
+; Zero byte allocas should be deleted.
+; CHECK: @test3
+; CHECK-NOT: alloca
 define void @test3() {
         %A = alloca { i32 }             ; <{ i32 }*> [#uses=1]
         %B = getelementptr { i32 }* %A, i32 0, i32 0            ; <i32*> [#uses=1]
@@ -30,3 +37,10 @@ define void @test3() {
         ret void
 }
 
+; CHECK: @test4
+; CHECK: = zext i32 %n to i64
+; CHECK: %A = alloca i32, i64 %
+define i32* @test4(i32 %n) {
+  %A = alloca i32, i32 %n
+  ret i32* %A
+}