[SROA] Split the alignment computation complete for the memcpy rewriting

to work independently for the slice side and the other side.

This allows us to only compute the minimum of the two when we actually
rewrite to a memcpy that needs to take the minimum, and preserve higher
alignment for one side or the other when rewriting to loads and stores.

This fix was inspired by seeing the result of some refactoring that
makes addrspace handling better.

llvm-svn: 202242

2 files changed, 32 insertions, 16 deletions

diff --git a/llvm/lib/Transforms/Scalar/SROA.cpp b/llvm/lib/Transforms/Scalar/SROA.cpp
index 9b819499099..859e3a79b7d 100644
--- a/llvm/lib/Transforms/Scalar/SROA.cpp
+++ b/llvm/lib/Transforms/Scalar/SROA.cpp
@@ -2494,10 +2494,7 @@ private:
     assert((IsDest && II.getRawDest() == OldPtr) ||
            (!IsDest && II.getRawSource() == OldPtr));
 
-    unsigned MinAlignment = II.getAlignment();
-    if (MinAlignment == 0)
-      MinAlignment = 1; // Fix the '0' alignment used by memcpy and memmove.
-    MinAlignment = MinAlign(MinAlignment, getSliceAlign());
+    unsigned SliceAlign = getSliceAlign();
 
     // For unsplit intrinsics, we simply modify the source and destination
     // pointers in place. This isn't just an optimization, it is a matter of
@@ -2513,9 +2510,10 @@ private:
       else
         II.setSource(AdjustedPtr);
 
-      if (II.getAlignment() > MinAlignment) {
+      if (II.getAlignment() > SliceAlign) {
         Type *CstTy = II.getAlignmentCst()->getType();
-        II.setAlignment(ConstantInt::get(CstTy, MinAlignment));
+        II.setAlignment(
+            ConstantInt::get(CstTy, MinAlign(II.getAlignment(), SliceAlign)));
       }
 
       DEBUG(dbgs() << "          to: " << II << "\n");
@@ -2564,10 +2562,8 @@ private:
     // Compute the relative offset for the other pointer within the transfer.
     unsigned IntPtrWidth = DL.getPointerSizeInBits();
     APInt OtherOffset(IntPtrWidth, NewBeginOffset - BeginOffset);
-
-    // Factor the offset other pointer's alignment into the requinerd minimum.
-    MinAlignment =
-        MinAlign(MinAlignment, OtherOffset.zextOrTrunc(64).getZExtValue());
+    unsigned OtherAlign = MinAlign(II.getAlignment() ? II.getAlignment() : 1,
+                                   OtherOffset.zextOrTrunc(64).getZExtValue());
 
     if (EmitMemCpy) {
       Type *OtherPtrTy = OtherPtr->getType();
@@ -2581,9 +2577,9 @@ private:
       Type *SizeTy = II.getLength()->getType();
       Constant *Size = ConstantInt::get(SizeTy, NewEndOffset - NewBeginOffset);
 
-      CallInst *New = IRB.CreateMemCpy(IsDest ? OurPtr : OtherPtr,
-                                       IsDest ? OtherPtr : OurPtr,
-                                       Size, MinAlignment, II.isVolatile());
+      CallInst *New = IRB.CreateMemCpy(
+          IsDest ? OurPtr : OtherPtr, IsDest ? OtherPtr : OurPtr, Size,
+          MinAlign(SliceAlign, OtherAlign), II.isVolatile());
       (void)New;
       DEBUG(dbgs() << "          to: " << *New << "\n");
       return false;
@@ -2612,9 +2608,13 @@ private:
 
     Value *SrcPtr = getAdjustedPtr(IRB, DL, OtherPtr, OtherOffset, OtherPtrTy,
                                    OtherPtr->getName() + ".");
+    unsigned SrcAlign = OtherAlign;
     Value *DstPtr = &NewAI;
-    if (!IsDest)
+    unsigned DstAlign = SliceAlign;
+    if (!IsDest) {
       std::swap(SrcPtr, DstPtr);
+      std::swap(SrcAlign, DstAlign);
+    }
 
     Value *Src;
     if (VecTy && !IsWholeAlloca && !IsDest) {
@@ -2628,7 +2628,7 @@ private:
       uint64_t Offset = NewBeginOffset - NewAllocaBeginOffset;
       Src = extractInteger(DL, IRB, Src, SubIntTy, Offset, "extract");
     } else {
-      Src = IRB.CreateAlignedLoad(SrcPtr, MinAlignment, II.isVolatile(),
+      Src = IRB.CreateAlignedLoad(SrcPtr, SrcAlign, II.isVolatile(),
                                   "copyload");
     }
 
@@ -2646,7 +2646,7 @@ private:
     }
 
     StoreInst *Store = cast<StoreInst>(
-        IRB.CreateAlignedStore(Src, DstPtr, MinAlignment, II.isVolatile()));
+        IRB.CreateAlignedStore(Src, DstPtr, DstAlign, II.isVolatile()));
     (void)Store;
     DEBUG(dbgs() << "          to: " << *Store << "\n");
     return !II.isVolatile();
diff --git a/llvm/test/Transforms/SROA/basictest.ll b/llvm/test/Transforms/SROA/basictest.ll
index 983c038316b..a3bf15fb7ac 100644
--- a/llvm/test/Transforms/SROA/basictest.ll
+++ b/llvm/test/Transforms/SROA/basictest.ll
@@ -1405,3 +1405,19 @@ entry:
   ret void
 }
 
+define void @test24(i8* %src, i8* %dst) {
+; CHECK-LABEL: @test24(
+; CHECK: alloca i64, align 16
+; CHECK: load volatile i64* %{{[^,]*}}, align 1
+; CHECK: store volatile i64 %{{[^,]*}}, i64* %{{[^,]*}}, align 16
+; CHECK: load volatile i64* %{{[^,]*}}, align 16
+; CHECK: store volatile i64 %{{[^,]*}}, i64* %{{[^,]*}}, align 1
+
+entry:
+  %a = alloca i64, align 16
+  %ptr = bitcast i64* %a to i8*
+  call void @llvm.memcpy.p0i8.p0i8.i32(i8* %ptr, i8* %src, i32 8, i32 1, i1 true)
+  call void @llvm.memcpy.p0i8.p0i8.i32(i8* %dst, i8* %ptr, i32 8, i32 1, i1 true)
+  ret void
+}
+