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Add a target-specific branchless method for double-width relational

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comparisons on x86.  Essentially, the way this works is that SUB+SBB sets
the relevant flags the same way a double-width CMP would.

This is a substantial improvement over the generic lowering in LLVM. The output
is also shorter than the gcc-generated output; I haven't done any detailed
benchmarking, though.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@127852 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Eli Friedman 2011-03-18 02:34:11 +00:00
parent a4f9839701
commit b4b8b0cc90
3 changed files with 103 additions and 16 deletions
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77
lib/Target/X86/X86ISelLowering.cpp
View File

@ -446,12 +446,13 @@ X86TargetLowering::X86TargetLowering(X86TargetMachine &TM)
setOperationAction(ISD::SETCC , MVT::i8 , Custom);
setOperationAction(ISD::SETCC , MVT::i16 , Custom);
setOperationAction(ISD::SETCC , MVT::i32 , Custom);
setOperationAction(ISD::SETCC , MVT::i64 , Custom);
setOperationAction(ISD::SETCC , MVT::f32 , Custom);
setOperationAction(ISD::SETCC , MVT::f64 , Custom);
setOperationAction(ISD::SETCC , MVT::f80 , Custom);
if (Subtarget->is64Bit()) {
setOperationAction(ISD::SELECT , MVT::i64 , Custom);
setOperationAction(ISD::SETCC , MVT::i64 , Custom);
setOperationAction(ISD::SETCC , MVT::i128 , Custom);
}
setOperationAction(ISD::EH_RETURN , MVT::Other, Custom);
@ -2839,7 +2840,7 @@ static unsigned TranslateX86CC(ISD::CondCode SetCCOpcode, bool isFP,
} else if (SetCCOpcode == ISD::SETLT && RHSC->isNullValue()) {
// X < 0 -> X == 0, jump on sign.
return X86::COND_S;
} else if (SetCCOpcode == ISD::SETLT && RHSC->getZExtValue() == 1) {
} else if (SetCCOpcode == ISD::SETLT && RHSC->isOne()) {
// X < 1 -> X <= 0
RHS = DAG.getConstant(0, RHS.getValueType());
return X86::COND_LE;
@ -7422,7 +7423,8 @@ SDValue X86TargetLowering::LowerSETCC(SDValue Op, SelectionDAG &DAG) const {
// Lower (X & (1 << N)) == 0 to BT(X, N).
// Lower ((X >>u N) & 1) != 0 to BT(X, N).
// Lower ((X >>s N) & 1) != 0 to BT(X, N).
if (Op0.getOpcode() == ISD::AND && Op0.hasOneUse() &&
if (isTypeLegal(Op0.getValueType()) &&
Op0.getOpcode() == ISD::AND && Op0.hasOneUse() &&
Op1.getOpcode() == ISD::Constant &&
cast<ConstantSDNode>(Op1)->isNullValue() &&
(CC == ISD::SETEQ || CC == ISD::SETNE)) {
@ -7434,7 +7436,7 @@ SDValue X86TargetLowering::LowerSETCC(SDValue Op, SelectionDAG &DAG) const {
// Look for X == 0, X == 1, X != 0, or X != 1. We can simplify some forms of
// these.
if (Op1.getOpcode() == ISD::Constant &&
(cast<ConstantSDNode>(Op1)->getZExtValue() == 1 ||
(cast<ConstantSDNode>(Op1)->isOne() ||
cast<ConstantSDNode>(Op1)->isNullValue()) &&
(CC == ISD::SETEQ || CC == ISD::SETNE)) {
@ -7457,6 +7459,73 @@ SDValue X86TargetLowering::LowerSETCC(SDValue Op, SelectionDAG &DAG) const {
if (X86CC == X86::COND_INVALID)
return SDValue();
if ((!Subtarget->is64Bit() && Op0.getValueType() == MVT::i64) ||
(Subtarget->is64Bit() && Op0.getValueType() == MVT::i128)) {
switch (X86CC) {
case X86::COND_E:
case X86::COND_NE:
case X86::COND_S:
case X86::COND_NS:
// Just use the generic lowering, which works well on x86.
return SDValue();
case X86::COND_B:
case X86::COND_AE:
case X86::COND_L:
case X86::COND_GE:
// Use SBB-based lowering.
break;
case X86::COND_A:
// Use SBB-based lowering; commute so ZF isn't used.
X86CC = X86::COND_B;
std::swap(Op0, Op1);
break;
case X86::COND_BE:
// Use SBB-based lowering; commute so ZF isn't used.
X86CC = X86::COND_AE;
std::swap(Op0, Op1);
break;
case X86::COND_G:
// Use SBB-based lowering; commute so ZF isn't used.
X86CC = X86::COND_L;
std::swap(Op0, Op1);
break;
case X86::COND_LE:
// Use SBB-based lowering; commute so ZF isn't used.
X86CC = X86::COND_GE;
std::swap(Op0, Op1);
break;
default:
assert(0 && "Unexpected X86CC.");
return SDValue();
}
MVT HalfType = getPointerTy();
// FIXME: Refactor this code out to implement ISD::SADDO and friends.
SDValue Op0Low = DAG.getNode(ISD::EXTRACT_ELEMENT, dl, HalfType,
Op0, DAG.getIntPtrConstant(0));
SDValue Op1Low = DAG.getNode(ISD::EXTRACT_ELEMENT, dl, HalfType,
Op1, DAG.getIntPtrConstant(0));
SDValue Op0High = DAG.getNode(ISD::EXTRACT_ELEMENT, dl, HalfType,
Op0, DAG.getIntPtrConstant(1));
SDValue Op1High = DAG.getNode(ISD::EXTRACT_ELEMENT, dl, HalfType,
Op1, DAG.getIntPtrConstant(1));
// Redirect some cases which will simplify to the generic expansion;
// X86ISD::SUB and X86ISD::SBB are not optimized well at the moment.
// FIXME: We really need to add DAGCombines for SUB/SBB/etc.
if (Op1Low.getOpcode() == ISD::Constant &&
cast<ConstantSDNode>(Op1Low)->isNullValue())
return SDValue();
if (Op0Low.getOpcode() == ISD::Constant &&
cast<ConstantSDNode>(Op0Low)->isAllOnesValue())
return SDValue();
SDValue res1, res2;
SDVTList VTList = DAG.getVTList(HalfType, MVT::i32);
res1 = DAG.getNode(X86ISD::SUB, dl, VTList, Op0Low, Op1Low).getValue(1);
res2 = DAG.getNode(X86ISD::SBB, dl, VTList, Op0High, Op1High,
res1).getValue(1);
return DAG.getNode(X86ISD::SETCC, dl, MVT::i8,
DAG.getConstant(X86CC, MVT::i8), res2);
}
SDValue EFLAGS = EmitCmp(Op0, Op1, X86CC, DAG);
return DAG.getNode(X86ISD::SETCC, dl, MVT::i8,
DAG.getConstant(X86CC, MVT::i8), EFLAGS);

39
test/CodeGen/X86/long-setcc.ll
View File

@ -1,18 +1,35 @@
; RUN: llc < %s -march=x86 | grep cmp | count 1
; RUN: llc < %s -march=x86 | grep shr | count 1
; RUN: llc < %s -march=x86 | grep xor | count 1
; RUN: llc < %s -march=x86 | FileCheck %s
define i1 @t1(i64 %x) nounwind {
%B = icmp slt i64 %x, 0
ret i1 %B
; General case
define i1 @t1(i64 %x, i64 %y) nounwind {
; CHECK: @t1
; CHECK: subl
; CHECK: sbbl
; CHECK: setl %al
%B = icmp slt i64 %x, %y
ret i1 %B
}
; Some special cases
define i1 @t2(i64 %x) nounwind {
%tmp = icmp ult i64 %x, 4294967296
ret i1 %tmp
; CHECK: @t2
; CHECK: shrl $31, %eax
%B = icmp slt i64 %x, 0
ret i1 %B
}
define i1 @t3(i32 %x) nounwind {
%tmp = icmp ugt i32 %x, -1
ret i1 %tmp
define i1 @t3(i64 %x) nounwind {
; CHECK: @t3
; CHECX: cmpl $0
; CHECX: sete %al
%tmp = icmp ult i64 %x, 4294967296
ret i1 %tmp
}
define i1 @t4(i64 %x) nounwind {
; CHECK: @t4
; CHECX: cmpl $0
; CHECX: setne %al
%tmp = icmp ugt i64 %x, 4294967295
ret i1 %tmp
}

3
test/CodeGen/X86/sext-i1.ll
View File

@ -39,7 +39,8 @@ entry:
; 32: t3:
; 32: cmpl $1
; 32: sbbl
; 32: cmpl
; 32: subl
; 32: sbbl
; 32: xorl
; 64: t3: