From 0fd353376b2741fc477c5fe05a5f18ae3abc4f60 Mon Sep 17 00:00:00 2001
From: Dan Gohman <gohman@apple.com>
Date: Tue, 3 Aug 2010 18:20:32 +0000
Subject: [PATCH] Make instcombine set explicit alignments on load or store
 instructions with alignment 0, so that subsequent passes don't need to bother
 checking the TargetData ABI size manually.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@110128 91177308-0d34-0410-b5e6-96231b3b80d8
---
 .../InstCombine/InstCombineLoadStoreAlloca.cpp     | 20 +++++++++----
 test/Transforms/InstCombine/align-addr.ll          | 33 ++++++++++++++++++++--
 test/Transforms/InstCombine/align-inc.ll           | 12 --------
 3 files changed, 45 insertions(+), 20 deletions(-)
 delete mode 100644 test/Transforms/InstCombine/align-inc.ll

diff --git a/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp b/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
index 5001896a5b3..b68fbc2db5c 100644
--- a/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
+++ b/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
@@ -146,10 +146,14 @@ Instruction *InstCombiner::visitLoadInst(LoadInst &LI) {
   if (TD) {
     unsigned KnownAlign =
       GetOrEnforceKnownAlignment(Op, TD->getPrefTypeAlignment(LI.getType()));
-    if (KnownAlign >
-        (LI.getAlignment() == 0 ? TD->getABITypeAlignment(LI.getType()) :
-                                  LI.getAlignment()))
+    unsigned LoadAlign = LI.getAlignment();
+    unsigned EffectiveLoadAlign = LoadAlign != 0 ? LoadAlign :
+      TD->getABITypeAlignment(LI.getType());
+
+    if (KnownAlign > EffectiveLoadAlign)
       LI.setAlignment(KnownAlign);
+    else if (LoadAlign == 0)
+      LI.setAlignment(EffectiveLoadAlign);
   }
 
   // load (cast X) --> cast (load X) iff safe.
@@ -411,10 +415,14 @@ Instruction *InstCombiner::visitStoreInst(StoreInst &SI) {
   if (TD) {
     unsigned KnownAlign =
       GetOrEnforceKnownAlignment(Ptr, TD->getPrefTypeAlignment(Val->getType()));
-    if (KnownAlign >
-        (SI.getAlignment() == 0 ? TD->getABITypeAlignment(Val->getType()) :
-                                  SI.getAlignment()))
+    unsigned StoreAlign = SI.getAlignment();
+    unsigned EffectiveStoreAlign = StoreAlign != 0 ? StoreAlign :
+      TD->getABITypeAlignment(Val->getType());
+
+    if (KnownAlign > EffectiveStoreAlign)
       SI.setAlignment(KnownAlign);
+    else if (StoreAlign == 0)
+      SI.setAlignment(EffectiveStoreAlign);
   }
 
   // Do really simple DSE, to catch cases where there are several consecutive
diff --git a/test/Transforms/InstCombine/align-addr.ll b/test/Transforms/InstCombine/align-addr.ll
index d8ad5a9864e..27916b98603 100644
--- a/test/Transforms/InstCombine/align-addr.ll
+++ b/test/Transforms/InstCombine/align-addr.ll
@@ -1,10 +1,13 @@
-; RUN: opt < %s -instcombine -S | grep {align 16} | count 1
+; RUN: opt < %s -instcombine -S | FileCheck %s
 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"
 
 ; Instcombine should be able to prove vector alignment in the
 ; presence of a few mild address computation tricks.
 
-define void @foo(i8* %b, i64 %n, i64 %u, i64 %y) nounwind  {
+; CHECK: @test0(
+; CHECK: align 16
+
+define void @test0(i8* %b, i64 %n, i64 %u, i64 %y) nounwind  {
 entry:
   %c = ptrtoint i8* %b to i64
   %d = and i64 %c, -16
@@ -29,3 +32,29 @@ return:
   ret void
 }
 
+; When we see a unaligned load from an insufficiently aligned global or
+; alloca, increase the alignment of the load, turning it into an aligned load.
+
+; CHECK: @test1(
+; CHECK: tmp = load
+; CHECK: GLOBAL{{.*}}align 16
+
+@GLOBAL = internal global [4 x i32] zeroinitializer
+
+define <16 x i8> @test1(<2 x i64> %x) {
+entry:
+	%tmp = load <16 x i8>* bitcast ([4 x i32]* @GLOBAL to <16 x i8>*), align 1
+	ret <16 x i8> %tmp
+}
+
+; When a load or store lacks an explicit alignment, add one.
+
+; CHECK: @test2(
+; CHECK: load double* %p, align 8
+; CHECK: store double %n, double* %p, align 8
+
+define double @test2(double* %p, double %n) nounwind {
+  %t = load double* %p
+  store double %n, double* %p
+  ret double %t
+}
diff --git a/test/Transforms/InstCombine/align-inc.ll b/test/Transforms/InstCombine/align-inc.ll
deleted file mode 100644
index 71512b3a149..00000000000
--- a/test/Transforms/InstCombine/align-inc.ll
+++ /dev/null
@@ -1,12 +0,0 @@
-; RUN: opt < %s -instcombine -S | grep {GLOBAL.*align 16}
-; RUN: opt < %s -instcombine -S | grep {tmp = load}
-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"
-
-@GLOBAL = internal global [4 x i32] zeroinitializer
-
-define <16 x i8> @foo(<2 x i64> %x) {
-entry:
-	%tmp = load <16 x i8>* bitcast ([4 x i32]* @GLOBAL to <16 x i8>*), align 1
-	ret <16 x i8> %tmp
-}
-
-- 
2.11.0