[llvm] r202242 - [SROA] Split the alignment computation complete for the memcpy rewriting

[Chandler Carruth]

Author: chandlerc
Date: Wed Feb 26 01:29:54 2014
New Revision: 202242

URL: http://llvm.org/viewvc/llvm-project?rev=202242&view=rev
Log:
[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.

Modified:
    llvm/trunk/lib/Transforms/Scalar/SROA.cpp
    llvm/trunk/test/Transforms/SROA/basictest.ll

Modified: llvm/trunk/lib/Transforms/Scalar/SROA.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/SROA.cpp?rev=202242&r1=202241&r2=202242&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Scalar/SROA.cpp (original)
+++ llvm/trunk/lib/Transforms/Scalar/SROA.cpp Wed Feb 26 01:29:54 2014
@@ -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();

Modified: llvm/trunk/test/Transforms/SROA/basictest.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/SROA/basictest.ll?rev=202242&r1=202241&r2=202242&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/SROA/basictest.ll (original)
+++ llvm/trunk/test/Transforms/SROA/basictest.ll Wed Feb 26 01:29:54 2014
@@ -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
+}
+