Fix instcombine to obey requested alignment when merging allocas.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@164117 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp b/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
index 6ecb4c52c4014c80e19d7aa1ba72a11dee373e09..5b6cf4a4a83f3daa85443a80f62d53732074aa2c 100644 (file)
--- a/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
+++ b/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
@@ -246,12 +246,16 @@ Instruction *InstCombiner::visitAllocaInst(AllocaInst &AI) {
           return &AI;
         }
 
+        // If the alignment of the entry block alloca is 0 (unspecified),
+        // assign it the preferred alignment.
+        if (EntryAI->getAlignment() == 0)
+          EntryAI->setAlignment(
+            TD->getPrefTypeAlignment(EntryAI->getAllocatedType()));
         // Replace this zero-sized alloca with the one at the start of the entry
         // block after ensuring that the address will be aligned enough for both
         // types.
-        unsigned MaxAlign =
-          std::max(TD->getPrefTypeAlignment(EntryAI->getAllocatedType()),
-                   TD->getPrefTypeAlignment(AI.getAllocatedType()));
+        unsigned MaxAlign = std::max(EntryAI->getAlignment(),
+                                     AI.getAlignment());
         EntryAI->setAlignment(MaxAlign);
         if (AI.getType() != EntryAI->getType())
           return new BitCastInst(EntryAI, AI.getType());

diff --git a/test/Transforms/InstCombine/2012-09-17-ZeroSizedAlloca.ll b/test/Transforms/InstCombine/2012-09-17-ZeroSizedAlloca.ll
new file mode 100644 (file)
index 0000000..ba025e9
--- /dev/null
+++ b/test/Transforms/InstCombine/2012-09-17-ZeroSizedAlloca.ll
@@ -0,0 +1,24 @@
+; RUN: opt -S -instcombine < %s | FileCheck %s
+
+; When merging zero sized alloca check that requested alignments of the allocas
+; are obeyed.
+
+@x = global i8* null, align 8
+@y = global i8* null, align 8
+
+target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64-S128"
+target triple = "x86_64-apple-macosx10.8.0"
+
+; CHECK: @f
+; CHECK-NEXT: alloca [0 x i8], align 1024
+; CHECK-NOT: alloca
+; CHECK: ret void
+define void @f() {
+  %1 = alloca [0 x i8], align 1
+  %2 = alloca [0 x i8], align 1024
+  %3 = getelementptr inbounds [0 x i8]* %1, i64 0, i64 0
+  %4 = getelementptr inbounds [0 x i8]* %2, i64 0, i64 0
+  store i8* %3, i8** @x, align 8
+  store i8* %4, i8** @y, align 8
+  ret void
+}