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

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

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
+}