When rewriting the pointer operand to a load or store which has

alignment guarantees attached, re-compute the alignment so that we
consider offsets which impact alignment.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@164690 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Transforms/Scalar/SROA.cpp

@@ -1992,6 +1992,9 @@ private:
     Value *NewPtr = getAdjustedAllocaPtr(IRB,
                                          LI.getPointerOperand()->getType());
     LI.setOperand(0, NewPtr);
+    if (LI.getAlignment())
+      LI.setAlignment(MinAlign(NewAI.getAlignment(),
+                               BeginOffset - NewAllocaBeginOffset));
     DEBUG(dbgs() << "          to: " << LI << "\n");
 
     deleteIfTriviallyDead(OldOp);
@@ -2043,6 +2046,9 @@ private:
     Value *NewPtr = getAdjustedAllocaPtr(IRB,
                                          SI.getPointerOperand()->getType());
     SI.setOperand(1, NewPtr);
+    if (SI.getAlignment())
+      SI.setAlignment(MinAlign(NewAI.getAlignment(),
+                               BeginOffset - NewAllocaBeginOffset));
     DEBUG(dbgs() << "          to: " << SI << "\n");
 
     deleteIfTriviallyDead(OldOp);

test/Transforms/SROA/alignment.ll

@@ -28,6 +28,24 @@ entry:
   ret void
 }
 
+define void @test2() {
+; CHECK: @test2
+; CHECK: alloca i16, align 2
+; CHECK: load i8* %{{.*}}, align 1
+; CHECK: store i8 42, i8* %{{.*}}, align 1
+; CHECK: ret void
+
+entry:
+  %a = alloca { i8, i8, i8, i8 }, align 2
+  %gep1 = getelementptr { i8, i8, i8, i8 }* %a, i32 0, i32 1
+  %cast1 = bitcast i8* %gep1 to i16*
+  store volatile i16 0, i16* %cast1
+  %gep2 = getelementptr { i8, i8, i8, i8 }* %a, i32 0, i32 2
+  %result = load i8* %gep2, align 2
+  store i8 42, i8* %gep2, align 2
+  ret void
+}
+
 define void @PR13920(<2 x i64>* %a, i16* %b) {
 ; Test that alignments on memcpy intrinsics get propagated to loads and stores.
 ; CHECK: @PR13920