[PATCH] D42871: [InstCombine] Simplify MemTransferInst's source and dest alignments separately

[Daniel Neilson via Phabricator via llvm-commits]

dneilson created this revision.
dneilson added a reviewer: majnemer.
Herald added a reviewer: bollu.

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. ( https://reviews.llvm.org/rL322965, https://reviews.llvm.org/rC322964, https://reviews.llvm.org/rL322963 )
Step 2) Expand the IRBuilder API to allow creation of memcpy/memmove with differing
source and dest alignments. ( https://reviews.llvm.org/rL323597 )
Step 3) Update Clang to use the new IRBuilder API. ( https://reviews.llvm.org/rC323617 )
Step 4) Update Polly to use the new IRBuilder API. ( https://reviews.llvm.org/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. ( https://reviews.llvm.org/rL323886, r323891 )
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


Repository:
  rL LLVM

https://reviews.llvm.org/D42871

Files:
  lib/Transforms/InstCombine/InstCombineCalls.cpp
  test/Transforms/InstCombine/memcpy-from-global.ll
  test/Transforms/InstCombine/memmove.ll


Index: test/Transforms/InstCombine/memmove.ll
===================================================================
--- test/Transforms/InstCombine/memmove.ll
+++ test/Transforms/InstCombine/memmove.ll
@@ -17,7 +17,7 @@
 define void @test2(i8* %A, i32 %N) {
   ;; dest can't alias source since we can't write to source!
   ;; CHECK-LABEL: test2
-  ;; CHECK-NEXT: call void @llvm.memcpy.p0i8.p0i8.i32(i8* align 1 %A, i8* align 1 getelementptr inbounds ([33 x i8], [33 x i8]* @S, i{{32|64}} 0, i{{32|64}} 0), i32 %N, i1 false)
+  ;; CHECK-NEXT: call void @llvm.memcpy.p0i8.p0i8.i32(i8* align 1 %A, i8* align 16 getelementptr inbounds ([33 x i8], [33 x i8]* @S, i{{32|64}} 0, i{{32|64}} 0), i32 %N, i1 false)
   ;; CHECK-NEXT: ret void
   call void @llvm.memmove.p0i8.p0i8.i32(i8* %A, i8* getelementptr inbounds ([33 x i8], [33 x i8]* @S, i32 0, i32 0), i32 %N, i1 false)
   ret void
Index: test/Transforms/InstCombine/memcpy-from-global.ll
===================================================================
--- test/Transforms/InstCombine/memcpy-from-global.ll
+++ test/Transforms/InstCombine/memcpy-from-global.ll
@@ -60,7 +60,7 @@
 ; CHECK-NEXT: getelementptr inbounds [124 x i8], [124 x i8]*
 
 ; use @G instead of %A
-; CHECK-NEXT: call void @llvm.memcpy.p0i8.p0i8.i64(i8* nonnull align 8 %{{.*}}, i8* align 8 getelementptr inbounds (%T, %T* @G, i64 0, i32 0)
+; CHECK-NEXT: call void @llvm.memcpy.p0i8.p0i8.i64(i8* nonnull align 8 %{{.*}}, i8* align 16 getelementptr inbounds (%T, %T* @G, i64 0, i32 0)
   call void @llvm.memcpy.p0i8.p0i8.i64(i8* align 4 %a, i8* align 4 bitcast (%T* @G to i8*), i64 124, i1 false)
   call void @llvm.memcpy.p0i8.p0i8.i64(i8* align 4 %b, i8* align 4 %a, i64 124, i1 false)
   call void @bar(i8* %b)
Index: lib/Transforms/InstCombine/InstCombineCalls.cpp
===================================================================
--- lib/Transforms/InstCombine/InstCombineCalls.cpp
+++ lib/Transforms/InstCombine/InstCombineCalls.cpp
@@ -184,14 +184,18 @@
 }
 
 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;
   }
 
@@ -237,8 +241,8 @@
 
   // If the memcpy/memmove provides better alignment info than we can
   // infer, use it.
-  SrcAlign = std::max(SrcAlign, CopyAlign);
-  DstAlign = std::max(DstAlign, CopyAlign);
+  SrcAlign = std::max(SrcAlign, CopySrcAlign);
+  DstAlign = std::max(DstAlign, CopyDstAlign);
 
   Value *Src = Builder.CreateBitCast(MI->getArgOperand(1), NewSrcPtrTy);
   Value *Dest = Builder.CreateBitCast(MI->getArgOperand(0), NewDstPtrTy);


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