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[X86] Improve mul w/ overflow codegen, to MUL8+SETO.

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Currently, @llvm.smul.with.overflow.i8 expands to 9 instructions, where
3 are really needed.

This adds X86ISD::UMUL8/SMUL8 SD nodes, and custom lowers them to
MUL8/IMUL8 + SETO.

i8 is a special case because there is no two/three operand variants of
(I)MUL8, so the first operand and return value need to go in AL/AX.

Also, we can't write patterns for these instructions: TableGen refuses
patterns where output operands don't match SDNode results. In this case,
instructions where the output operand is an implicitly defined register.

A related special case (and FIXME) exists for MUL8 (X86InstrArith.td):

  // FIXME: Used for 8-bit mul, ignore result upper 8 bits.
  // This probably ought to be moved to a def : Pat<> if the
  // syntax can be accepted.
  [(set AL, (mul AL, GR8:$src)), (implicit EFLAGS)]

Ideally, these go away with UMUL8, but we still need to improve TableGen
support of implicit operands in patterns.

Before this change:
  movsbl  %sil, %eax
  movsbl  %dil, %ecx
  imull   %eax, %ecx
  movb    %cl, %al
  sarb    $7, %al
  movzbl  %al, %eax
  movzbl  %ch, %esi
  cmpl    %eax, %esi
  setne   %al

After:
  movb    %dil, %al
  imulb   %sil
  seto    %al

Also, remove a made-redundant testcase for PR19858, and enable more FastISel
ALU-overflow tests for SelectionDAG too.

Differential Revision: http://reviews.llvm.org/D5809


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@220516 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Ahmed Bougacha 2014-10-23 21:55:31 +00:00
parent 78f043e90a
commit 4d962b05ca
5 changed files with 39 additions and 42 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

19
lib/Target/X86/X86ISelDAGToDAG.cpp
View File

@ -2218,6 +2218,25 @@ SDNode *X86DAGToDAGISel::Select(SDNode *Node) {
return CurDAG->SelectNodeTo(Node, ShlOp, NVT, SDValue(New, 0),
getI8Imm(ShlVal));
}
case X86ISD::UMUL8:
case X86ISD::SMUL8: {
SDValue N0 = Node->getOperand(0);
SDValue N1 = Node->getOperand(1);
Opc = (Opcode == X86ISD::SMUL8 ? X86::IMUL8r : X86::MUL8r);
SDValue InFlag = CurDAG->getCopyToReg(CurDAG->getEntryNode(), dl, X86::AL,
N0, SDValue()).getValue(1);
SDVTList VTs = CurDAG->getVTList(NVT, MVT::i32);
SDValue Ops[] = {N1, InFlag};
SDNode *CNode = CurDAG->getMachineNode(Opc, dl, VTs, Ops);
ReplaceUses(SDValue(Node, 0), SDValue(CNode, 0));
ReplaceUses(SDValue(Node, 1), SDValue(CNode, 1));
return nullptr;
}
case X86ISD::UMUL: {
SDValue N0 = Node->getOperand(0);
SDValue N1 = Node->getOperand(1);

10
lib/Target/X86/X86ISelLowering.cpp
View File

@ -1597,9 +1597,6 @@ void X86TargetLowering::resetOperationActions() {
setOperationAction(ISD::UMULO, VT, Custom);
}
// There are no 8-bit 3-address imul/mul instructions
setOperationAction(ISD::SMULO, MVT::i8, Expand);
setOperationAction(ISD::UMULO, MVT::i8, Expand);
if (!Subtarget->is64Bit()) {
// These libcalls are not available in 32-bit.
@ -18190,10 +18187,15 @@ static SDValue LowerXALUO(SDValue Op, SelectionDAG &DAG) {
Cond = X86::COND_B;
break;
case ISD::SMULO:
BaseOp = X86ISD::SMUL;
BaseOp = N->getValueType(0) == MVT::i8 ? X86ISD::SMUL8 : X86ISD::SMUL;
Cond = X86::COND_O;
break;
case ISD::UMULO: { // i64, i8 = umulo lhs, rhs --> i64, i64, i32 umul lhs,rhs
if (N->getValueType(0) == MVT::i8) {
BaseOp = X86ISD::UMUL8;
Cond = X86::COND_O;
break;
}
SDVTList VTs = DAG.getVTList(N->getValueType(0), N->getValueType(0),
MVT::i32);
SDValue Sum = DAG.getNode(X86ISD::UMUL, DL, VTs, LHS, RHS);

3
lib/Target/X86/X86ISelLowering.h
View File

@ -301,6 +301,9 @@ namespace llvm {
UMUL, // LOW, HI, FLAGS = umul LHS, RHS
// 8-bit SMUL/UMUL - AX, FLAGS = smul8/umul8 AL, RHS
SMUL8, UMUL8,
// MUL_IMM - X86 specific multiply by immediate.
MUL_IMM,

24
test/CodeGen/X86/i8-umulo.ll
View File

@ -1,24 +0,0 @@
; RUN: llc -mcpu=generic -march=x86 < %s | FileCheck %s
; PR19858
declare {i8, i1} @llvm.umul.with.overflow.i8(i8 %a, i8 %b)
define i8 @testumulo(i32 %argc) {
; CHECK: imull
; CHECK: testb %{{.+}}, %{{.+}}
; CHECK: je [[NOOVERFLOWLABEL:.+]]
; CHECK: {{.*}}[[NOOVERFLOWLABEL]]:
; CHECK-NEXT: movb
; CHECK-NEXT: retl
top:
%RHS = trunc i32 %argc to i8
%umul = call { i8, i1 } @llvm.umul.with.overflow.i8(i8 25, i8 %RHS)
%ex = extractvalue { i8, i1 } %umul, 1
br i1 %ex, label %overflow, label %nooverlow
overflow:
ret i8 %RHS
nooverlow:
%umul.value = extractvalue { i8, i1 } %umul, 0
ret i8 %umul.value
}

25
test/CodeGen/X86/xaluo.ll
View File

@ -123,12 +123,9 @@ entry:
; Check boundary conditions for large immediates.
define zeroext i1 @saddo.i64imm2(i64 %v1, i64* %res) {
entry:
; SDAG-LABEL: saddo.i64imm2
; SDAG: addq $-2147483648, %rdi
; SDAG-NEXT: seto %al
; FAST-LABEL: saddo.i64imm2
; FAST: addq $-2147483648, %rdi
; FAST-NEXT: seto %al
; CHECK-LABEL: saddo.i64imm2
; CHECK: addq $-2147483648, %rdi
; CHECK-NEXT: seto %al
%t = call {i64, i1} @llvm.sadd.with.overflow.i64(i64 %v1, i64 -2147483648)
%val = extractvalue {i64, i1} %t, 0
%obit = extractvalue {i64, i1} %t, 1
@ -297,10 +294,10 @@ entry:
; SMULO
define zeroext i1 @smulo.i8(i8 %v1, i8 %v2, i8* %res) {
entry:
; FAST-LABEL: smulo.i8
; FAST: movb %dil, %al
; FAST-NEXT: imulb %sil
; FAST-NEXT: seto %cl
; CHECK-LABEL: smulo.i8
; CHECK: movb %dil, %al
; CHECK-NEXT: imulb %sil
; CHECK-NEXT: seto %cl
%t = call {i8, i1} @llvm.smul.with.overflow.i8(i8 %v1, i8 %v2)
%val = extractvalue {i8, i1} %t, 0
%obit = extractvalue {i8, i1} %t, 1
@ -347,10 +344,10 @@ entry:
; UMULO
define zeroext i1 @umulo.i8(i8 %v1, i8 %v2, i8* %res) {
entry:
; FAST-LABEL: umulo.i8
; FAST: movb %dil, %al
; FAST-NEXT: mulb %sil
; FAST-NEXT: seto %cl
; CHECK-LABEL: umulo.i8
; CHECK: movb %dil, %al
; CHECK-NEXT: mulb %sil
; CHECK-NEXT: seto %cl
%t = call {i8, i1} @llvm.umul.with.overflow.i8(i8 %v1, i8 %v2)
%val = extractvalue {i8, i1} %t, 0
%obit = extractvalue {i8, i1} %t, 1