[PATCH][SLP-Vectorizer]Always set alignment of vectorized LD/ST in SLP-Vectorizer

[Yi Jiang]

Hi,

This patch is to fix the run time error exposed by enabling SLP in LTO.  

This bug is about the alignment of vectorized memory operation. Now the SLP vectorizer will pass the alignment info from the scalar LD/ST to vectorized version. It is usually okay but sometimes the scalar LD/ST has no alignment at all. In this case, the vectorized LD/ST also has no alignment and the instcombine will set up the alignment according to the type. This will result in wrong alignment info for vectorized LD/ST and the Codegen may generate wrong instruction. In our fix, we set the alignment according to Scalar LD/ST's type if no alignment info. 


Index: lib/Transforms/Vectorize/SLPVectorizer.cpp
===================================================================
--- lib/Transforms/Vectorize/SLPVectorizer.cpp	(revision 207849)
+++ lib/Transforms/Vectorize/SLPVectorizer.cpp	(working copy)
@@ -1618,6 +1618,8 @@
                                            VecTy->getPointerTo(AS));
      unsigned Alignment = LI->getAlignment();
      LI = Builder.CreateLoad(VecPtr);
+      if (!Alignment)
+        Alignment = DL->getABITypeAlignment(LI->getPointerOperand()->getType());
      LI->setAlignment(Alignment);
      E->VectorizedValue = LI;
      return propagateMetadata(LI, E->Scalars);
@@ -1637,6 +1639,8 @@
      Value *VecPtr = Builder.CreateBitCast(SI->getPointerOperand(),
                                            VecTy->getPointerTo(AS));
      StoreInst *S = Builder.CreateStore(VecValue, VecPtr);
+      if (!Alignment)
+        Alignment = DL->getABITypeAlignment(SI->getPointerOperand()->getType());
      S->setAlignment(Alignment);
      E->VectorizedValue = S;
      return propagateMetadata(S, E->Scalars);
Index: test/Transforms/SLPVectorizer/X86/align.ll
===================================================================
--- test/Transforms/SLPVectorizer/X86/align.ll	(revision 0)
+++ test/Transforms/SLPVectorizer/X86/align.ll	(working copy)
@@ -0,0 +1,27 @@
+; RUN: opt < %s -basicaa -slp-vectorizer -S -mtriple=x86_64-apple-macosx10.8.0 -mcpu=corei7-avx | FileCheck %s
+
+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"
+
+; Simple 3-pair chain with loads and stores
+; CHECK: test1
+define void @test1(double* %a, double* %b, double* %c) {
+entry:
+  %agg.tmp.i.i.sroa.0 = alloca [3 x double], align 16
+; CHECK: %[[V0:[0-9]+]] = load <2 x double>* %[[V2:[0-9]+]], align 8
+  %i0 = load double* %a 
+  %i1 = load double* %b 
+  %mul = fmul double %i0, %i1
+  %store1 = getelementptr inbounds [3 x double]* %agg.tmp.i.i.sroa.0, i64 0, i64 1
+  %store2 = getelementptr inbounds [3 x double]* %agg.tmp.i.i.sroa.0, i64 0, i64 2
+  %arrayidx3 = getelementptr inbounds double* %a, i64 1
+  %i3 = load double* %arrayidx3, align 8
+  %arrayidx4 = getelementptr inbounds double* %b, i64 1
+  %i4 = load double* %arrayidx4, align 8
+  %mul5 = fmul double %i3, %i4
+; CHECK: store <2 x double> %[[V1:[0-9]+]], <2 x double>* %[[V2:[0-9]+]], align 8
+  store double %mul, double* %store1
+  store double %mul5, double* %store2, align 16
+; CHECK: ret
+  ret void
+}