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generalize the previous code to use the full generality of LEA

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for i32/i64 expressions (we could also do i16 on cpus where
i16 lea is fast, but I didn't add this).  On the example, we now
generate:

_test:
	movl	4(%esp), %eax
	cmpl	$42, (%eax)
	setl	%al
	movzbl	%al, %eax
	leal	4(%eax,%eax,8), %eax
	ret

instead of:

_test:
	movl	4(%esp), %eax
	cmpl	$41, (%eax)
	movl	$4, %ecx
	movl	$13, %eax
	cmovg	%ecx, %eax
	ret



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@66869 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2009-03-13 05:53:31 +00:00
parent 97a29a5fee
commit cee56e7d33
2 changed files with 121 additions and 13 deletions
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122
lib/Target/X86/X86ISelLowering.cpp
View File

@ -8188,25 +8188,26 @@ static SDValue PerformSELECTCombine(SDNode *N, SelectionDAG &DAG,
// If this is a select between two integer constants, try to do some
// optimizations.
if (ConstantSDNode *LHSC = dyn_cast<ConstantSDNode>(LHS)) {
if (ConstantSDNode *RHSC = dyn_cast<ConstantSDNode>(RHS))
if (ConstantSDNode *TrueC = dyn_cast<ConstantSDNode>(LHS)) {
if (ConstantSDNode *FalseC = dyn_cast<ConstantSDNode>(RHS))
// Don't do this for crazy integer types.
if (DAG.getTargetLoweringInfo().isTypeLegal(LHS.getValueType())) {
// If this is efficiently invertible, canonicalize the LHSC/RHSC values
// so that LHSC (the true value) is larger than RHSC (the false value).
// so that TrueC (the true value) is larger than FalseC.
bool NeedsCondInvert = false;
if (LHSC->getAPIntValue().ult(RHSC->getAPIntValue()) &&
if (TrueC->getAPIntValue().ult(FalseC->getAPIntValue()) &&
// Efficiently invertible.
(Cond.getOpcode() == ISD::SETCC || // setcc -> invertible.
(Cond.getOpcode() == ISD::XOR && // xor(X, C) -> invertible.
isa<ConstantSDNode>(Cond.getOperand(1))))) {
NeedsCondInvert = true;
std::swap(LHSC, RHSC);
std::swap(TrueC, FalseC);
}
// Optimize C ? 8 : 0 -> zext(C) << 3. Likewise for any pow2/0.
if (RHSC->getAPIntValue() == 0 && LHSC->getAPIntValue().isPowerOf2()) {
if (FalseC->getAPIntValue() == 0 &&
TrueC->getAPIntValue().isPowerOf2()) {
if (NeedsCondInvert) // Invert the condition if needed.
Cond = DAG.getNode(ISD::XOR, DL, Cond.getValueType(), Cond,
DAG.getConstant(1, Cond.getValueType()));
@ -8214,22 +8215,67 @@ static SDValue PerformSELECTCombine(SDNode *N, SelectionDAG &DAG,
// Zero extend the condition if needed.
Cond = DAG.getNode(ISD::ZERO_EXTEND, DL, LHS.getValueType(), Cond);
unsigned ShAmt = LHSC->getAPIntValue().logBase2();
unsigned ShAmt = TrueC->getAPIntValue().logBase2();
return DAG.getNode(ISD::SHL, DL, LHS.getValueType(), Cond,
DAG.getConstant(ShAmt, MVT::i8));
}
// Optimize Cond ? cst+1 : cst -> zext(setcc(C)+cst.
if (RHSC->getAPIntValue()+1 == LHSC->getAPIntValue()) {
if (FalseC->getAPIntValue()+1 == TrueC->getAPIntValue()) {
if (NeedsCondInvert) // Invert the condition if needed.
Cond = DAG.getNode(ISD::XOR, DL, Cond.getValueType(), Cond,
DAG.getConstant(1, Cond.getValueType()));
// Zero extend the condition if needed.
Cond = DAG.getNode(ISD::ZERO_EXTEND, DL, RHSC->getValueType(0), Cond);
Cond = DAG.getNode(ISD::ZERO_EXTEND, DL,
FalseC->getValueType(0), Cond);
return DAG.getNode(ISD::ADD, DL, Cond.getValueType(), Cond,
SDValue(RHSC, 0));
SDValue(FalseC, 0));
}
// Optimize cases that will turn into an LEA instruction. This requires
// an i32 or i64 and an efficient multiplier (1, 2, 3, 4, 5, 8, 9).
if (N->getValueType(0) == MVT::i32 || N->getValueType(0) == MVT::i64) {
uint64_t Diff = TrueC->getZExtValue()-FalseC->getZExtValue();
if (N->getValueType(0) == MVT::i32) Diff = (unsigned)Diff;
bool isFastMultiplier = false;
if (Diff < 10) {
switch ((unsigned char)Diff) {
default: break;
case 1: // result = add base, cond
case 2: // result = lea base( , cond*2)
case 3: // result = lea base(cond, cond*2)
case 4: // result = lea base( , cond*4)
case 5: // result = lea base(cond, cond*4)
case 8: // result = lea base( , cond*8)
case 9: // result = lea base(cond, cond*8)
isFastMultiplier = true;
break;
}
}
if (isFastMultiplier) {
APInt Diff = TrueC->getAPIntValue()-FalseC->getAPIntValue();
if (NeedsCondInvert) // Invert the condition if needed.
Cond = DAG.getNode(ISD::XOR, DL, Cond.getValueType(), Cond,
DAG.getConstant(1, Cond.getValueType()));
// Zero extend the condition if needed.
Cond = DAG.getNode(ISD::ZERO_EXTEND, DL, FalseC->getValueType(0),
Cond);
// Scale the condition by the difference.
if (Diff != 1)
Cond = DAG.getNode(ISD::MUL, DL, Cond.getValueType(), Cond,
DAG.getConstant(Diff, Cond.getValueType()));
// Add the base if non-zero.
if (FalseC->getAPIntValue() != 0)
Cond = DAG.getNode(ISD::ADD, DL, Cond.getValueType(), Cond,
SDValue(FalseC, 0));
return Cond;
}
}
}
}
@ -8260,6 +8306,8 @@ static SDValue PerformCMOVCombine(SDNode *N, SelectionDAG &DAG,
}
// Optimize C ? 8 : 0 -> zext(setcc(C)) << 3. Likewise for any pow2/0.
// This is efficient for any integer data type (including i8/i16) and
// shift amount.
if (FalseC->getAPIntValue() == 0 && TrueC->getAPIntValue().isPowerOf2()) {
SDValue Cond = N->getOperand(3);
Cond = DAG.getNode(X86ISD::SETCC, DL, MVT::i8,
@ -8275,21 +8323,69 @@ static SDValue PerformCMOVCombine(SDNode *N, SelectionDAG &DAG,
return DCI.CombineTo(N, Cond, SDValue());
return Cond;
}
// Optimize Cond ? cst+1 : cst -> zext(setcc(C)+cst.
// Optimize Cond ? cst+1 : cst -> zext(setcc(C)+cst. This is efficient
// for any integer data type, including i8/i16.
if (FalseC->getAPIntValue()+1 == TrueC->getAPIntValue()) {
SDValue Cond = N->getOperand(3);
Cond = DAG.getNode(X86ISD::SETCC, DL, MVT::i8,
DAG.getConstant(CC, MVT::i8), Cond);
// Zero extend the condition if needed.
Cond = DAG.getNode(ISD::ZERO_EXTEND, DL, FalseC->getValueType(0), Cond);
Cond = DAG.getNode(ISD::ZERO_EXTEND, DL,
FalseC->getValueType(0), Cond);
Cond = DAG.getNode(ISD::ADD, DL, Cond.getValueType(), Cond,
SDValue(FalseC, 0));
if (N->getNumValues() == 2) // Dead flag value?
return DCI.CombineTo(N, Cond, SDValue());
return Cond;
}
// Optimize cases that will turn into an LEA instruction. This requires
// an i32 or i64 and an efficient multiplier (1, 2, 3, 4, 5, 8, 9).
if (N->getValueType(0) == MVT::i32 || N->getValueType(0) == MVT::i64) {
uint64_t Diff = TrueC->getZExtValue()-FalseC->getZExtValue();
if (N->getValueType(0) == MVT::i32) Diff = (unsigned)Diff;
bool isFastMultiplier = false;
if (Diff < 10) {
switch ((unsigned char)Diff) {
default: break;
case 1: // result = add base, cond
case 2: // result = lea base( , cond*2)
case 3: // result = lea base(cond, cond*2)
case 4: // result = lea base( , cond*4)
case 5: // result = lea base(cond, cond*4)
case 8: // result = lea base( , cond*8)
case 9: // result = lea base(cond, cond*8)
isFastMultiplier = true;
break;
}
}
if (isFastMultiplier) {
APInt Diff = TrueC->getAPIntValue()-FalseC->getAPIntValue();
SDValue Cond = N->getOperand(3);
Cond = DAG.getNode(X86ISD::SETCC, DL, MVT::i8,
DAG.getConstant(CC, MVT::i8), Cond);
// Zero extend the condition if needed.
Cond = DAG.getNode(ISD::ZERO_EXTEND, DL, FalseC->getValueType(0),
Cond);
// Scale the condition by the difference.
if (Diff != 1)
Cond = DAG.getNode(ISD::MUL, DL, Cond.getValueType(), Cond,
DAG.getConstant(Diff, Cond.getValueType()));
// Add the base if non-zero.
if (FalseC->getAPIntValue() != 0)
Cond = DAG.getNode(ISD::ADD, DL, Cond.getValueType(), Cond,
SDValue(FalseC, 0));
if (N->getNumValues() == 2) // Dead flag value?
return DCI.CombineTo(N, Cond, SDValue());
return Cond;
}
}
}
}
return SDValue();

12
test/CodeGen/X86/select-no-cmov.ll
View File

@ -12,3 +12,15 @@ entry:
%iftmp.0.0 = select i1 %1, i32 -1, i32 -2 ; <i32> [#uses=1]
ret i32 %iftmp.0.0
}
; setl %al
; movzbl %al, %eax
; leal 4(%eax,%eax,8), %eax
define i32 @test2(i32* nocapture %P) nounwind readonly {
entry:
%0 = load i32* %P, align 4 ; <i32> [#uses=1]
%1 = icmp sgt i32 %0, 41 ; <i1> [#uses=1]
%iftmp.0.0 = select i1 %1, i32 4, i32 13 ; <i32> [#uses=1]
ret i32 %iftmp.0.0
}