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Generate CMN when comparing a short int with minus

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@216651 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
David Xu
2014-08-28 04:59:53 +00:00
parent cf3736085b
commit 5ca793561e
2 changed files with 87 additions and 3 deletions
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44
lib/Target/AArch64/AArch64ISelLowering.cpp
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@@ -1117,6 +1117,8 @@ static SDValue emitComparison(SDValue LHS, SDValue RHS, ISD::CondCode CC,
static SDValue getAArch64Cmp(SDValue LHS, SDValue RHS, ISD::CondCode CC, static SDValue getAArch64Cmp(SDValue LHS, SDValue RHS, ISD::CondCode CC,
SDValue &AArch64cc, SelectionDAG &DAG, SDLoc dl) { SDValue &AArch64cc, SelectionDAG &DAG, SDLoc dl) {
SDValue Cmp;
AArch64CC::CondCode AArch64CC;
if (ConstantSDNode *RHSC = dyn_cast<ConstantSDNode>(RHS.getNode())) { if (ConstantSDNode *RHSC = dyn_cast<ConstantSDNode>(RHS.getNode())) {
EVT VT = RHS.getValueType(); EVT VT = RHS.getValueType();
uint64_t C = RHSC->getZExtValue(); uint64_t C = RHSC->getZExtValue();
@@ -1171,9 +1173,45 @@ static SDValue getAArch64Cmp(SDValue LHS, SDValue RHS, ISD::CondCode CC,
} }
} }
} }
// The imm operand of ADDS is an unsigned immediate, in the range 0 to 4095.
SDValue Cmp = emitComparison(LHS, RHS, CC, dl, DAG); // For the i8 operand, the largest immediate is 255, so this can be easily
AArch64CC::CondCode AArch64CC = changeIntCCToAArch64CC(CC); // encoded in the compare instruction. For the i16 operand, however, the
// largest immediate cannot be encoded in the compare.
// Therefore, use a sign extending load and cmn to avoid materializing the -1
// constant. For example,
// movz w1, #65535
// ldrh w0, [x0, #0]
// cmp w0, w1
// >
// ldrsh w0, [x0, #0]
// cmn w0, #1
// Fundamental, we're relying on the property that (zext LHS) == (zext RHS)
// if and only if (sext LHS) == (sext RHS). The checks are in place to ensure
// both the LHS and RHS are truely zero extended and to make sure the
// transformation is profitable.
if ((CC == ISD::SETEQ || CC == ISD::SETNE) && isa<ConstantSDNode>(RHS)) {
if ((cast<ConstantSDNode>(RHS)->getZExtValue() >> 16 == 0) &&
isa<LoadSDNode>(LHS)) {
if (cast<LoadSDNode>(LHS)->getExtensionType() == ISD::ZEXTLOAD &&
cast<LoadSDNode>(LHS)->getMemoryVT() == MVT::i16 &&
LHS.getNode()->hasNUsesOfValue(1, 0)) {
int16_t ValueofRHS = cast<ConstantSDNode>(RHS)->getZExtValue();
if (ValueofRHS < 0 && isLegalArithImmed(-ValueofRHS)) {
SDValue SExt =
DAG.getNode(ISD::SIGN_EXTEND_INREG, dl, LHS.getValueType(), LHS,
DAG.getValueType(MVT::i16));
Cmp = emitComparison(SExt,
DAG.getConstant(ValueofRHS, RHS.getValueType()),
CC, dl, DAG);
AArch64CC = changeIntCCToAArch64CC(CC);
AArch64cc = DAG.getConstant(AArch64CC, MVT::i32);
return Cmp;
}
}
}
}
Cmp = emitComparison(LHS, RHS, CC, dl, DAG);
AArch64CC = changeIntCCToAArch64CC(CC);
AArch64cc = DAG.getConstant(AArch64CC, MVT::i32); AArch64cc = DAG.getConstant(AArch64CC, MVT::i32);
return Cmp; return Cmp;
} }

46
test/CodeGen/AArch64/cmpwithshort.ll Normal file
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@@ -0,0 +1,46 @@
; RUN: llc -O3 -march=aarch64 < %s | FileCheck %s
define i16 @test_1cmp_signed_1(i16* %ptr1) {
; CHECK-LABLE: @test_1cmp_signed_1
; CHECK: ldrsh
; CHECK-NEXT: cmn
entry:
%addr = getelementptr inbounds i16* %ptr1, i16 0
%val = load i16* %addr, align 2
%cmp = icmp eq i16 %val, -1
br i1 %cmp, label %if, label %if.then
if:
ret i16 1
if.then:
ret i16 0
}
define i16 @test_1cmp_signed_2(i16* %ptr1) {
; CHECK-LABLE: @test_1cmp_signed_2
; CHECK: ldrsh
; CHECK-NEXT: cmn
entry:
%addr = getelementptr inbounds i16* %ptr1, i16 0
%val = load i16* %addr, align 2
%cmp = icmp sge i16 %val, -1
br i1 %cmp, label %if, label %if.then
if:
ret i16 1
if.then:
ret i16 0
}
define i16 @test_1cmp_unsigned_1(i16* %ptr1) {
; CHECK-LABLE: @test_1cmp_unsigned_1
; CHECK: ldrsh
; CHECK-NEXT: cmn
entry:
%addr = getelementptr inbounds i16* %ptr1, i16 0
%val = load i16* %addr, align 2
%cmp = icmp uge i16 %val, -1
br i1 %cmp, label %if, label %if.then
if:
ret i16 1
if.then:
ret i16 0
}