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[SystemZ] Optimize X [!=]= Y in cases where X - Y or Y - X is also computed

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In those cases it's better to compare the result of the subtraction
against zero.

llvm-svn: 197239
This commit is contained in:
Richard Sandiford 2013-12-13 15:50:30 +00:00
parent 7ae30a86de
commit 5a37a68afd
2 changed files with 41 additions and 0 deletions
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21
lib/Target/SystemZ/SystemZISelLowering.cpp
View File

@ -1271,6 +1271,26 @@ static unsigned reverseCCMask(unsigned CCMask) {
(CCMask & SystemZ::CCMASK_CMP_UO));
}
// Check whether C tests for equality between X and Y and whether X - Y
// or Y - X is also computed. In that case it's better to compare the
// result of the subtraction against zero.
static void adjustForSubtraction(SelectionDAG &DAG, Comparison &C) {
if (C.CCMask == SystemZ::CCMASK_CMP_EQ ||
C.CCMask == SystemZ::CCMASK_CMP_NE) {
for (SDNode::use_iterator I = C.Op0->use_begin(), E = C.Op0->use_end();
I != E; ++I) {
SDNode *N = *I;
if (N->getOpcode() == ISD::SUB &&
((N->getOperand(0) == C.Op0 && N->getOperand(1) == C.Op1) ||
(N->getOperand(0) == C.Op1 && N->getOperand(1) == C.Op0))) {
C.Op0 = SDValue(N, 0);
C.Op1 = DAG.getConstant(0, N->getValueType(0));
return;
}
}
}
}
// Check whether C compares a floating-point value with zero and if that
// floating-point value is also negated. In this case we can use the
// negation to set CC, so avoiding separate LOAD AND TEST and
@ -1540,6 +1560,7 @@ static Comparison getCmp(SelectionDAG &DAG, SDValue CmpOp0, SDValue CmpOp1,
C.CCMask &= ~SystemZ::CCMASK_CMP_UO;
adjustZeroCmp(DAG, C);
adjustSubwordCmp(DAG, C);
adjustForSubtraction(DAG, C);
}
if (shouldSwapCmpOperands(C)) {

20
test/CodeGen/SystemZ/int-cmp-44.ll
View File

@ -845,3 +845,23 @@ store:
exit:
ret i64 %ext
}
; Try a form of f7 in which the subtraction operands are compared directly.
define i32 @f41(i32 %a, i32 %b, i32 *%dest) {
; CHECK-LABEL: f41:
; CHECK: s %r2, 0(%r4)
; CHECK-NEXT: jne .L{{.*}}
; CHECK: br %r14
entry:
%cur = load i32 *%dest
%res = sub i32 %a, %cur
%cmp = icmp ne i32 %a, %cur
br i1 %cmp, label %exit, label %store
store:
store i32 %b, i32 *%dest
br label %exit
exit:
ret i32 %res
}