[llvm] [X86] For minsize, use size for alignment, rather than actual alignment (PR #87003)
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llvm-commits at lists.llvm.org
Fri Apr 5 11:07:06 PDT 2024
https://github.com/AtariDreams updated https://github.com/llvm/llvm-project/pull/87003
>From 267bb33603092170a892160a604dee45967001c9 Mon Sep 17 00:00:00 2001
From: Rose <gfunni234 at gmail.com>
Date: Thu, 28 Mar 2024 16:19:34 -0400
Subject: [PATCH] [X86] For minsize, use size for alignment, rather than actual
alignment
If we have minsize, then don't care about the alignment.
On x86, the CPU doesn't care and neither should you.
As long as the count is aligned, we can use less instructions.
---
llvm/lib/Target/X86/X86SelectionDAGInfo.cpp | 119 ++++++++++-----
.../CodeGen/X86/memset-vs-memset-inline.ll | 135 +-----------------
2 files changed, 85 insertions(+), 169 deletions(-)
diff --git a/llvm/lib/Target/X86/X86SelectionDAGInfo.cpp b/llvm/lib/Target/X86/X86SelectionDAGInfo.cpp
index 7c630a2b0da080..ab5386cc4c76a1 100644
--- a/llvm/lib/Target/X86/X86SelectionDAGInfo.cpp
+++ b/llvm/lib/Target/X86/X86SelectionDAGInfo.cpp
@@ -67,10 +67,27 @@ SDValue X86SelectionDAGInfo::EmitTargetCodeForMemset(
// The libc version is likely to be faster for these cases. It can use the
// address value and run time information about the CPU.
if (Alignment < Align(4) || !ConstantSize ||
- ConstantSize->getZExtValue() > Subtarget.getMaxInlineSizeThreshold())
+ ConstantSize->getZExtValue() > Subtarget.getMaxInlineSizeThreshold())
return SDValue();
+ // If we have minsize, then don't care about the alignment.
+ // On x86, the CPU doesn't care and neither should you.
+ // As long as the count is aligned, we can use the minimum number of
+ // instructions without always having to resort to strosb.
+ //
+ // Because this is a feature specific to x86, we must handle it here.
uint64_t SizeVal = ConstantSize->getZExtValue();
+ if (DAG.getMachineFunction().getFunction().hasMinSize()) {
+ if ((SizeVal & 7) == 0 && Subtarget.is64Bit())
+ Alignment = Align(8);
+ else if ((SizeVal & 3) == 0)
+ Alignment = Align(4);
+ else if ((SizeVal & 1) == 0)
+ Alignment = Align(2);
+ else
+ Alignment = Align(1);
+ }
+
SDValue InGlue;
EVT AVT;
SDValue Count;
@@ -103,51 +120,56 @@ SDValue X86SelectionDAGInfo::EmitTargetCodeForMemset(
Count = DAG.getIntPtrConstant(SizeVal, dl);
}
- if (AVT.bitsGT(MVT::i8)) {
- unsigned UBytes = AVT.getSizeInBits() / 8;
- Count = DAG.getIntPtrConstant(SizeVal / UBytes, dl);
- BytesLeft = SizeVal % UBytes;
- }
-
+ const uint64_t BlockBytes = AVT.getSizeInBits() / 8;
+ const uint64_t BlockCount = SizeVal / BlockBytes;
+ Count = DAG.getIntPtrConstant(BlockCount, dl);
+ BytesLeft = SizeVal % BlockBytes;
Chain = DAG.getCopyToReg(Chain, dl, ValReg, DAG.getConstant(Val, dl, AVT),
InGlue);
InGlue = Chain.getValue(1);
} else {
AVT = MVT::i8;
- Count = DAG.getIntPtrConstant(SizeVal, dl);
- Chain = DAG.getCopyToReg(Chain, dl, X86::AL, Val, InGlue);
+ Count = DAG.getIntPtrConstant(SizeVal, dl);
+ Chain = DAG.getCopyToReg(Chain, dl, X86::AL, Val, InGlue);
InGlue = Chain.getValue(1);
}
bool Use64BitRegs = Subtarget.isTarget64BitLP64();
- Chain = DAG.getCopyToReg(Chain, dl, Use64BitRegs ? X86::RCX : X86::ECX,
- Count, InGlue);
+ Chain = DAG.getCopyToReg(Chain, dl, Use64BitRegs ? X86::RCX : X86::ECX, Count,
+ InGlue);
InGlue = Chain.getValue(1);
- Chain = DAG.getCopyToReg(Chain, dl, Use64BitRegs ? X86::RDI : X86::EDI,
- Dst, InGlue);
+ Chain = DAG.getCopyToReg(Chain, dl, Use64BitRegs ? X86::RDI : X86::EDI, Dst,
+ InGlue);
InGlue = Chain.getValue(1);
SDVTList Tys = DAG.getVTList(MVT::Other, MVT::Glue);
- SDValue Ops[] = { Chain, DAG.getValueType(AVT), InGlue };
- Chain = DAG.getNode(X86ISD::REP_STOS, dl, Tys, Ops);
-
- if (BytesLeft) {
- // Handle the last 1 - 7 bytes.
- unsigned Offset = SizeVal - BytesLeft;
- EVT AddrVT = Dst.getValueType();
- EVT SizeVT = Size.getValueType();
-
- Chain =
- DAG.getMemset(Chain, dl,
- DAG.getNode(ISD::ADD, dl, AddrVT, Dst,
- DAG.getConstant(Offset, dl, AddrVT)),
- Val, DAG.getConstant(BytesLeft, dl, SizeVT), Alignment,
- isVolatile, AlwaysInline,
- /* isTailCall */ false, DstPtrInfo.getWithOffset(Offset));
- }
+ SDValue Ops[] = {Chain, DAG.getValueType(AVT), InGlue};
+ SDValue RepStos = DAG.getNode(X86ISD::REP_STOS, dl, Tys, Ops);
+
+ /// RepStos can process the whole length.
+ //
+ // Because we changed the alignment earlier in the function to work on size
+ // when we have the minsize attribute, this is guaranteed to be 0 when we get
+ // here.
+ if (BytesLeft == 0)
+ return RepStos;
- // TODO: Use a Tokenfactor, as in memcpy, instead of a single chain.
- return Chain;
+ // Handle the last 1 - 7 bytes.
+ SmallVector<SDValue, 4> Results;
+ Results.push_back(RepStos);
+ unsigned Offset = SizeVal - BytesLeft;
+ EVT AddrVT = Dst.getValueType();
+ EVT SizeVT = Size.getValueType();
+
+ Results.push_back(
+ DAG.getMemset(Chain, dl,
+ DAG.getNode(ISD::ADD, dl, AddrVT, Dst,
+ DAG.getConstant(Offset, dl, AddrVT)),
+ Val, DAG.getConstant(BytesLeft, dl, SizeVT), Alignment,
+ isVolatile, /* isAlwaysInline */ true,
+ /* isTailCall */ false, DstPtrInfo.getWithOffset(Offset)));
+
+ return DAG.getNode(ISD::TokenFactor, dl, MVT::Other, Results);
}
/// Emit a single REP MOVS{B,W,D,Q} instruction.
@@ -220,13 +242,39 @@ static SDValue emitConstantSizeRepmov(
assert(!Subtarget.hasERMSB() && "No efficient RepMovs");
/// We assume runtime memcpy will do a better job for unaligned copies when
/// ERMS is not present.
- if (!AlwaysInline && (Alignment.value() & 3) != 0)
+ if (!AlwaysInline && (Alignment < Align(4)))
return SDValue();
+ // If we have minsize, then don't care about the alignment.
+ // On x86, the CPU doesn't care and neither should you.
+ // As long as the count is aligned, we can use the minimum number of
+ // instructions without always having to resort to movsb
+ //
+ // Because this is a feature specific to x86, we must handle it here.
+ if (DAG.getMachineFunction().getFunction().hasMinSize()) {
+ if ((Size & 7) == 0 && Subtarget.is64Bit())
+ Alignment = Align(8);
+ else if ((Size & 3) == 0)
+ Alignment = Align(4);
+ else if ((Size & 1) == 0)
+ Alignment = Align(2);
+ else
+ Alignment = Align(1);
+ }
+
const MVT BlockType = getOptimalRepmovsType(Subtarget, Alignment);
const uint64_t BlockBytes = BlockType.getSizeInBits() / 8;
const uint64_t BlockCount = Size / BlockBytes;
const uint64_t BytesLeft = Size % BlockBytes;
+
+ if (DAG.getMachineFunction().getFunction().hasMinSize()) {
+ // Use the one instruction determined. Because we changed the alignment
+ // earlier in the function to work on size when we have the minsize
+ // attribute, it is guaranteed to process the entire length.
+ return emitRepmovs(Subtarget, DAG, dl, Chain, Dst, Src,
+ DAG.getIntPtrConstant(BlockCount, dl), BlockType);
+ }
+
SDValue RepMovs =
emitRepmovs(Subtarget, DAG, dl, Chain, Dst, Src,
DAG.getIntPtrConstant(BlockCount, dl), BlockType);
@@ -237,11 +285,6 @@ static SDValue emitConstantSizeRepmov(
assert(BytesLeft && "We have leftover at this point");
- /// In case we optimize for size we use repmovsb even if it's less efficient
- /// so we can save the loads/stores of the leftover.
- if (DAG.getMachineFunction().getFunction().hasMinSize())
- return emitRepmovsB(Subtarget, DAG, dl, Chain, Dst, Src, Size);
-
// Handle the last 1 - 7 bytes.
SmallVector<SDValue, 4> Results;
Results.push_back(RepMovs);
diff --git a/llvm/test/CodeGen/X86/memset-vs-memset-inline.ll b/llvm/test/CodeGen/X86/memset-vs-memset-inline.ll
index b8fdd936b43895..16022c6cbb3934 100644
--- a/llvm/test/CodeGen/X86/memset-vs-memset-inline.ll
+++ b/llvm/test/CodeGen/X86/memset-vs-memset-inline.ll
@@ -28,137 +28,10 @@ define void @regular_memset_calls_external_function(ptr %a, i8 %value) nounwind
define void @inlined_set_doesnt_call_external_function(ptr %a, i8 %value) nounwind {
; CHECK-LABEL: inlined_set_doesnt_call_external_function:
; CHECK: # %bb.0:
-; CHECK-NEXT: movzbl %sil, %ecx
-; CHECK-NEXT: movabsq $72340172838076673, %rax # imm = 0x101010101010101
-; CHECK-NEXT: imulq %rcx, %rax
-; CHECK-NEXT: movq %rax, 1016(%rdi)
-; CHECK-NEXT: movq %rax, 1008(%rdi)
-; CHECK-NEXT: movq %rax, 1000(%rdi)
-; CHECK-NEXT: movq %rax, 992(%rdi)
-; CHECK-NEXT: movq %rax, 984(%rdi)
-; CHECK-NEXT: movq %rax, 976(%rdi)
-; CHECK-NEXT: movq %rax, 968(%rdi)
-; CHECK-NEXT: movq %rax, 960(%rdi)
-; CHECK-NEXT: movq %rax, 952(%rdi)
-; CHECK-NEXT: movq %rax, 944(%rdi)
-; CHECK-NEXT: movq %rax, 936(%rdi)
-; CHECK-NEXT: movq %rax, 928(%rdi)
-; CHECK-NEXT: movq %rax, 920(%rdi)
-; CHECK-NEXT: movq %rax, 912(%rdi)
-; CHECK-NEXT: movq %rax, 904(%rdi)
-; CHECK-NEXT: movq %rax, 896(%rdi)
-; CHECK-NEXT: movq %rax, 888(%rdi)
-; CHECK-NEXT: movq %rax, 880(%rdi)
-; CHECK-NEXT: movq %rax, 872(%rdi)
-; CHECK-NEXT: movq %rax, 864(%rdi)
-; CHECK-NEXT: movq %rax, 856(%rdi)
-; CHECK-NEXT: movq %rax, 848(%rdi)
-; CHECK-NEXT: movq %rax, 840(%rdi)
-; CHECK-NEXT: movq %rax, 832(%rdi)
-; CHECK-NEXT: movq %rax, 824(%rdi)
-; CHECK-NEXT: movq %rax, 816(%rdi)
-; CHECK-NEXT: movq %rax, 808(%rdi)
-; CHECK-NEXT: movq %rax, 800(%rdi)
-; CHECK-NEXT: movq %rax, 792(%rdi)
-; CHECK-NEXT: movq %rax, 784(%rdi)
-; CHECK-NEXT: movq %rax, 776(%rdi)
-; CHECK-NEXT: movq %rax, 768(%rdi)
-; CHECK-NEXT: movq %rax, 760(%rdi)
-; CHECK-NEXT: movq %rax, 752(%rdi)
-; CHECK-NEXT: movq %rax, 744(%rdi)
-; CHECK-NEXT: movq %rax, 736(%rdi)
-; CHECK-NEXT: movq %rax, 728(%rdi)
-; CHECK-NEXT: movq %rax, 720(%rdi)
-; CHECK-NEXT: movq %rax, 712(%rdi)
-; CHECK-NEXT: movq %rax, 704(%rdi)
-; CHECK-NEXT: movq %rax, 696(%rdi)
-; CHECK-NEXT: movq %rax, 688(%rdi)
-; CHECK-NEXT: movq %rax, 680(%rdi)
-; CHECK-NEXT: movq %rax, 672(%rdi)
-; CHECK-NEXT: movq %rax, 664(%rdi)
-; CHECK-NEXT: movq %rax, 656(%rdi)
-; CHECK-NEXT: movq %rax, 648(%rdi)
-; CHECK-NEXT: movq %rax, 640(%rdi)
-; CHECK-NEXT: movq %rax, 632(%rdi)
-; CHECK-NEXT: movq %rax, 624(%rdi)
-; CHECK-NEXT: movq %rax, 616(%rdi)
-; CHECK-NEXT: movq %rax, 608(%rdi)
-; CHECK-NEXT: movq %rax, 600(%rdi)
-; CHECK-NEXT: movq %rax, 592(%rdi)
-; CHECK-NEXT: movq %rax, 584(%rdi)
-; CHECK-NEXT: movq %rax, 576(%rdi)
-; CHECK-NEXT: movq %rax, 568(%rdi)
-; CHECK-NEXT: movq %rax, 560(%rdi)
-; CHECK-NEXT: movq %rax, 552(%rdi)
-; CHECK-NEXT: movq %rax, 544(%rdi)
-; CHECK-NEXT: movq %rax, 536(%rdi)
-; CHECK-NEXT: movq %rax, 528(%rdi)
-; CHECK-NEXT: movq %rax, 520(%rdi)
-; CHECK-NEXT: movq %rax, 512(%rdi)
-; CHECK-NEXT: movq %rax, 504(%rdi)
-; CHECK-NEXT: movq %rax, 496(%rdi)
-; CHECK-NEXT: movq %rax, 488(%rdi)
-; CHECK-NEXT: movq %rax, 480(%rdi)
-; CHECK-NEXT: movq %rax, 472(%rdi)
-; CHECK-NEXT: movq %rax, 464(%rdi)
-; CHECK-NEXT: movq %rax, 456(%rdi)
-; CHECK-NEXT: movq %rax, 448(%rdi)
-; CHECK-NEXT: movq %rax, 440(%rdi)
-; CHECK-NEXT: movq %rax, 432(%rdi)
-; CHECK-NEXT: movq %rax, 424(%rdi)
-; CHECK-NEXT: movq %rax, 416(%rdi)
-; CHECK-NEXT: movq %rax, 408(%rdi)
-; CHECK-NEXT: movq %rax, 400(%rdi)
-; CHECK-NEXT: movq %rax, 392(%rdi)
-; CHECK-NEXT: movq %rax, 384(%rdi)
-; CHECK-NEXT: movq %rax, 376(%rdi)
-; CHECK-NEXT: movq %rax, 368(%rdi)
-; CHECK-NEXT: movq %rax, 360(%rdi)
-; CHECK-NEXT: movq %rax, 352(%rdi)
-; CHECK-NEXT: movq %rax, 344(%rdi)
-; CHECK-NEXT: movq %rax, 336(%rdi)
-; CHECK-NEXT: movq %rax, 328(%rdi)
-; CHECK-NEXT: movq %rax, 320(%rdi)
-; CHECK-NEXT: movq %rax, 312(%rdi)
-; CHECK-NEXT: movq %rax, 304(%rdi)
-; CHECK-NEXT: movq %rax, 296(%rdi)
-; CHECK-NEXT: movq %rax, 288(%rdi)
-; CHECK-NEXT: movq %rax, 280(%rdi)
-; CHECK-NEXT: movq %rax, 272(%rdi)
-; CHECK-NEXT: movq %rax, 264(%rdi)
-; CHECK-NEXT: movq %rax, 256(%rdi)
-; CHECK-NEXT: movq %rax, 248(%rdi)
-; CHECK-NEXT: movq %rax, 240(%rdi)
-; CHECK-NEXT: movq %rax, 232(%rdi)
-; CHECK-NEXT: movq %rax, 224(%rdi)
-; CHECK-NEXT: movq %rax, 216(%rdi)
-; CHECK-NEXT: movq %rax, 208(%rdi)
-; CHECK-NEXT: movq %rax, 200(%rdi)
-; CHECK-NEXT: movq %rax, 192(%rdi)
-; CHECK-NEXT: movq %rax, 184(%rdi)
-; CHECK-NEXT: movq %rax, 176(%rdi)
-; CHECK-NEXT: movq %rax, 168(%rdi)
-; CHECK-NEXT: movq %rax, 160(%rdi)
-; CHECK-NEXT: movq %rax, 152(%rdi)
-; CHECK-NEXT: movq %rax, 144(%rdi)
-; CHECK-NEXT: movq %rax, 136(%rdi)
-; CHECK-NEXT: movq %rax, 128(%rdi)
-; CHECK-NEXT: movq %rax, 120(%rdi)
-; CHECK-NEXT: movq %rax, 112(%rdi)
-; CHECK-NEXT: movq %rax, 104(%rdi)
-; CHECK-NEXT: movq %rax, 96(%rdi)
-; CHECK-NEXT: movq %rax, 88(%rdi)
-; CHECK-NEXT: movq %rax, 80(%rdi)
-; CHECK-NEXT: movq %rax, 72(%rdi)
-; CHECK-NEXT: movq %rax, 64(%rdi)
-; CHECK-NEXT: movq %rax, 56(%rdi)
-; CHECK-NEXT: movq %rax, 48(%rdi)
-; CHECK-NEXT: movq %rax, 40(%rdi)
-; CHECK-NEXT: movq %rax, 32(%rdi)
-; CHECK-NEXT: movq %rax, 24(%rdi)
-; CHECK-NEXT: movq %rax, 16(%rdi)
-; CHECK-NEXT: movq %rax, 8(%rdi)
-; CHECK-NEXT: movq %rax, (%rdi)
+; CHECK-NEXT: movl %esi, %eax
+; CHECK-NEXT: movl $1024, %ecx # imm = 0x400
+; CHECK-NEXT: # kill: def $al killed $al killed $eax
+; CHECK-NEXT: rep;stosb %al, %es:(%rdi)
; CHECK-NEXT: retq
tail call void @llvm.memset.inline.p0.i64(ptr %a, i8 %value, i64 1024, i1 0)
ret void
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