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optimize the case of cond ? 42 : 41 and friends. This compiles the

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example to:

_test:
	movl	4(%esp), %eax
	cmpl	$41, (%eax)
	setg	%al
	movzbl	%al, %eax
	orl	$4294967294, %eax
	ret

instead of:

        movl    4(%esp), %eax
        cmpl    $41, (%eax)
	movl	$4294967294, %ecx
	movl	$4294967295, %eax
	cmova	%ecx, %eax
	ret

which is smaller in code size and faster. rdar://6668608



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@66868 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2009-03-13 05:22:11 +00:00
parent 0582ae99ba
commit 97a29a5fee
2 changed files with 41 additions and 0 deletions
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27
lib/Target/X86/X86ISelLowering.cpp
View File

@ -8218,6 +8218,18 @@ static SDValue PerformSELECTCombine(SDNode *N, SelectionDAG &DAG,
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 (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);
return DAG.getNode(ISD::ADD, DL, Cond.getValueType(), Cond,
SDValue(RHSC, 0));
}
}
}
@ -8263,6 +8275,21 @@ static SDValue PerformCMOVCombine(SDNode *N, SelectionDAG &DAG,
return DCI.CombineTo(N, Cond, SDValue());
return Cond;
}
// Optimize Cond ? cst+1 : cst -> zext(setcc(C)+cst.
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::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();

14
test/CodeGen/X86/select-no-cmov.ll Normal file
View File

@ -0,0 +1,14 @@
; RUN: llvm-as < %s | llc | not grep cmov
target datalayout = "e-p:32:32:32-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:32:64-f32:32:32-f64:32:64-v64:64:64-v128:128:128-a0:0:64-f80:128:128"
target triple = "i386-apple-darwin7"
; Should compile to setcc | -2.
; rdar://6668608
define i32 @test(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 -1, i32 -2 ; <i32> [#uses=1]
ret i32 %iftmp.0.0
}