[InstCombine] Simplify MemTransferInst's source and dest alignments separately

Summary:
This change is part of step five in the series of changes to remove alignment argument from
memcpy/memmove/memset in favour of alignment attributes. In particular, this changes the
InstCombine pass to cease using the deprecated MemoryIntrinsic::getAlignment() method, and
instead we use the separate getSourceAlignment and getDestAlignment APIs to simplify
the source and destination alignment attributes separately.

Steps:
Step 1) Remove alignment parameter and create alignment parameter attributes for
memcpy/memmove/memset. ( rL322965, rC322964, rL322963 )
Step 2) Expand the IRBuilder API to allow creation of memcpy/memmove with differing
source and dest alignments. ( rL323597 )
Step 3) Update Clang to use the new IRBuilder API. ( rC323617 )
Step 4) Update Polly to use the new IRBuilder API. ( rL323618 )
Step 5) Update LLVM passes that create memcpy/memmove calls to use the new IRBuilder API,
and those that use use MemIntrinsicInst::[get|set]Alignment() to use [get|set]DestAlignment()
and [get|set]SourceAlignment() instead. ( rL323886, rL323891, rL324148, rL324273, rL324278,
rL324384, rL324395, rL324402, rL324626, rL324642, rL324653, rL324654, rL324773, rL324774,
rL324781, rL324784, rL324955 )
Step 6) Remove the single-alignment IRBuilder API for memcpy/memmove, and the
MemIntrinsicInst::[get|set]Alignment() methods.

Reference
   http://lists.llvm.org/pipermail/llvm-dev/2015-August/089384.html
   http://lists.llvm.org/pipermail/llvm-commits/Week-of-Mon-20151109/312083.html

Reviewers: majnemer, bollu, efriedma

Reviewed By: efriedma

Subscribers: efriedma, llvm-commits

Differential Revision: https://reviews.llvm.org/D42871

llvm-svn: 324960

1 files changed, 16 insertions, 15 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
index 2ad37c03376..e2a109cfa03 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
@@ -184,14 +184,18 @@ InstCombiner::SimplifyElementUnorderedAtomicMemCpy(AtomicMemCpyInst *AMI) {
 }
 
 Instruction *InstCombiner::SimplifyMemTransfer(MemIntrinsic *MI) {
-  unsigned DstAlign = getKnownAlignment(MI->getArgOperand(0), DL, MI, &AC, &DT);
-  unsigned SrcAlign = getKnownAlignment(MI->getArgOperand(1), DL, MI, &AC, &DT);
-  unsigned MinAlign = std::min(DstAlign, SrcAlign);
-  unsigned CopyAlign = MI->getAlignment();
-
-  // FIXME: Check & simplify source & dest alignments separately
-  if (CopyAlign < MinAlign) {
-    MI->setAlignment(MinAlign);
+  unsigned DstAlign = getKnownAlignment(MI->getRawDest(), DL, MI, &AC, &DT);
+  unsigned CopyDstAlign = MI->getDestAlignment();
+  if (CopyDstAlign < DstAlign){
+    MI->setDestAlignment(DstAlign);
+    return MI;
+  }
+
+  auto* MTI = cast<MemTransferInst>(MI);
+  unsigned SrcAlign = getKnownAlignment(MTI->getRawSource(), DL, MI, &AC, &DT);
+  unsigned CopySrcAlign = MTI->getSourceAlignment();
+  if (CopySrcAlign < SrcAlign) {
+    MTI->setSourceAlignment(SrcAlign);
     return MI;
   }
 
@@ -235,15 +239,11 @@ Instruction *InstCombiner::SimplifyMemTransfer(MemIntrinsic *MI) {
       CopyMD = cast<MDNode>(M->getOperand(2));
   }
 
-  // If the memcpy/memmove provides better alignment info than we can
-  // infer, use it.
-  SrcAlign = std::max(SrcAlign, CopyAlign);
-  DstAlign = std::max(DstAlign, CopyAlign);
-
   Value *Src = Builder.CreateBitCast(MI->getArgOperand(1), NewSrcPtrTy);
   Value *Dest = Builder.CreateBitCast(MI->getArgOperand(0), NewDstPtrTy);
   LoadInst *L = Builder.CreateLoad(Src, MI->isVolatile());
-  L->setAlignment(SrcAlign);
+  // Alignment from the mem intrinsic will be better, so use it.
+  L->setAlignment(CopySrcAlign);
   if (CopyMD)
     L->setMetadata(LLVMContext::MD_tbaa, CopyMD);
   MDNode *LoopMemParallelMD =
@@ -252,7 +252,8 @@ Instruction *InstCombiner::SimplifyMemTransfer(MemIntrinsic *MI) {
     L->setMetadata(LLVMContext::MD_mem_parallel_loop_access, LoopMemParallelMD);
 
   StoreInst *S = Builder.CreateStore(L, Dest, MI->isVolatile());
-  S->setAlignment(DstAlign);
+  // Alignment from the mem intrinsic will be better, so use it.
+  S->setAlignment(CopyDstAlign);
   if (CopyMD)
     S->setMetadata(LLVMContext::MD_tbaa, CopyMD);
   if (LoopMemParallelMD)