From 6893cd76152e805291c3c9f36fa81b330846434d Mon Sep 17 00:00:00 2001
From: Dan Gohman <gohman@apple.com>
Date: Tue, 13 Jan 2009 20:18:38 +0000
Subject: [PATCH] Make instcombine ensure that all allocas are explicitly
 aligned at at least their preferred alignment.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@62176 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Transforms/Scalar/InstructionCombining.cpp  | 17 +++++++++++------
 .../InstCombine/2009-01-08-AlignAlloca.ll       |  4 +++-
 .../InstCombine/loadstore-alignment.ll          |  2 +-
 3 files changed, 15 insertions(+), 8 deletions(-)

diff --git a/lib/Transforms/Scalar/InstructionCombining.cpp b/lib/Transforms/Scalar/InstructionCombining.cpp
index ee3596bde43..f640915386d 100644
--- a/lib/Transforms/Scalar/InstructionCombining.cpp
+++ b/lib/Transforms/Scalar/InstructionCombining.cpp
@@ -10775,12 +10775,17 @@ Instruction *InstCombiner::visitAllocationInst(AllocationInst &AI) {
     }
   }
 
-  // If alloca'ing a zero byte object, replace the alloca with a null pointer.
-  // Note that we only do this for alloca's, because malloc should allocate and
-  // return a unique pointer, even for a zero byte allocation.
-  if (isa<AllocaInst>(AI) && AI.getAllocatedType()->isSized() &&
-      TD->getTypePaddedSize(AI.getAllocatedType()) == 0)
-    return ReplaceInstUsesWith(AI, Constant::getNullValue(AI.getType()));
+  if (isa<AllocaInst>(AI) && AI.getAllocatedType()->isSized()) {
+    // If alloca'ing a zero byte object, replace the alloca with a null pointer.
+    // Note that we only do this for alloca's, because malloc should allocate and
+    // return a unique pointer, even for a zero byte allocation.
+    if (TD->getTypePaddedSize(AI.getAllocatedType()) == 0)
+      return ReplaceInstUsesWith(AI, Constant::getNullValue(AI.getType()));
+
+    // If the alignment is 0 (unspecified), assign it the preferred alignment.
+    if (AI.getAlignment() == 0)
+      AI.setAlignment(TD->getPrefTypeAlignment(AI.getAllocatedType()));
+  }
 
   return 0;
 }
diff --git a/test/Transforms/InstCombine/2009-01-08-AlignAlloca.ll b/test/Transforms/InstCombine/2009-01-08-AlignAlloca.ll
index c4c79a948ca..82b923ac95c 100644
--- a/test/Transforms/InstCombine/2009-01-08-AlignAlloca.ll
+++ b/test/Transforms/InstCombine/2009-01-08-AlignAlloca.ll
@@ -1,4 +1,6 @@
-; RUN: llvm-as < %s | opt -instcombine | llvm-dis | grep {, align 4} | count 4
+; RUN: llvm-as < %s | opt -instcombine | llvm-dis > %t
+; RUN: grep {, align 4} %t | count 3
+; RUN: grep {, align 8} %t | count 3
 ; rdar://6480438
 target datalayout = "e-p:32:32:32-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:32:64-f32:32:32-f64:32:64-v64:64:64-v128:128:128-a0:0:64-f80:128:128"
 target triple = "i386-apple-darwin9.6"
diff --git a/test/Transforms/InstCombine/loadstore-alignment.ll b/test/Transforms/InstCombine/loadstore-alignment.ll
index 82be575b328..ebea3e4fe83 100644
--- a/test/Transforms/InstCombine/loadstore-alignment.ll
+++ b/test/Transforms/InstCombine/loadstore-alignment.ll
@@ -1,4 +1,4 @@
-; RUN: llvm-as < %s | opt -instcombine | llvm-dis | grep {, align 16} | count 12
+; RUN: llvm-as < %s | opt -instcombine | llvm-dis | grep {, align 16} | count 14
 
 @x = external global <2 x i64>, align 16
 @xx = external global [13 x <2 x i64>], align 16