[AArch64] Teach AArch64TargetLowering::getOptimalMemOpType to consider alignment

restrictions when choosing a type for small-memcpy inlining in
SelectionDAGBuilder.

This ensures that the loads and stores output for the memcpy won't be further
expanded during legalization, which would cause the total number of instructions
for the memcpy to exceed (often significantly) the inlining thresholds.

<rdar://problem/17829180>

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@234462 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Target/AArch64/AArch64ISelLowering.cpp b/lib/Target/AArch64/AArch64ISelLowering.cpp
index 901e5b9..4fbd5b1 100644 (file)
--- a/lib/Target/AArch64/AArch64ISelLowering.cpp
+++ b/lib/Target/AArch64/AArch64ISelLowering.cpp
@@ -6664,7 +6664,17 @@ EVT AArch64TargetLowering::getOptimalMemOpType(uint64_t Size, unsigned DstAlign,
        (allowsMisalignedMemoryAccesses(MVT::f128, 0, 1, &Fast) && Fast)))
     return MVT::f128;
 
-  return Size >= 8 ? MVT::i64 : MVT::i32;
+  if (Size >= 8 &&
+      (memOpAlign(SrcAlign, DstAlign, 8) ||
+       (allowsMisalignedMemoryAccesses(MVT::i64, 0, 1, &Fast) && Fast)))
+    return MVT::i64;
+
+  if (Size >= 4 &&
+      (memOpAlign(SrcAlign, DstAlign, 4) ||
+       (allowsMisalignedMemoryAccesses(MVT::i32, 0, 1, &Fast) && Fast)))
+    return MVT::i64;
+
+  return MVT::Other;
 }
 
 // 12-bit optionally shifted immediates are legal for adds.

diff --git a/test/CodeGen/AArch64/arm64-misaligned-memcpy-inline.ll b/test/CodeGen/AArch64/arm64-misaligned-memcpy-inline.ll
new file mode 100644 (file)
index 0000000..e71b824
--- /dev/null
+++ b/test/CodeGen/AArch64/arm64-misaligned-memcpy-inline.ll
@@ -0,0 +1,14 @@
+; RUN: llc -march=arm64 -aarch64-strict-align < %s | FileCheck %s
+
+; Small (16-bytes here) unaligned memcpys should stay memcpy calls if
+; strict-alignment is turned on.
+define void @t0(i8* %out, i8* %in) {
+; CHECK-LABEL: t0:
+; CHECK:         orr w2, wzr, #0x10
+; CHECK-NEXT:    bl _memcpy
+entry:
+  call void @llvm.memcpy.p0i8.p0i8.i64(i8* %out, i8* %in, i64 16, i32 1, i1 false)
+  ret void
+}
+
+declare void @llvm.memcpy.p0i8.p0i8.i64(i8* nocapture, i8* nocapture readonly, i64, i32, i1)