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[SystemZ] Optimize comparisons with truncated extended loads

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If the extension of a loaded value is compared against zero and used in
other arithmetic, InstCombine will change the comparison to use the
unextended load.  It's also possible that the comparison could be against
the unextended load from the outset.

In DAG form this becomes a truncation of an extending load.  We want to
strip the truncation if possible so that we can use load-and-test instructions.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@197804 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Richard Sandiford 2013-12-20 11:56:02 +00:00
parent 1fd4e55828
commit 23c9710636
2 changed files with 46 additions and 2 deletions
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26
lib/Target/SystemZ/SystemZISelLowering.cpp
View File

@ -1339,6 +1339,27 @@ static void adjustForLTGFR(Comparison &C) {
}
}
// If C compares the truncation of an extending load, try to compare
// the untruncated value instead. This exposes more opportunities to
// reuse CC.
static void adjustICmpTruncate(SelectionDAG &DAG, Comparison &C) {
if (C.Op0.getOpcode() == ISD::TRUNCATE &&
C.Op0.getOperand(0).getOpcode() == ISD::LOAD &&
C.Op1.getOpcode() == ISD::Constant &&
cast<ConstantSDNode>(C.Op1)->getZExtValue() == 0) {
LoadSDNode *L = cast<LoadSDNode>(C.Op0.getOperand(0));
if (L->getMemoryVT().getStoreSizeInBits()
<= C.Op0.getValueType().getSizeInBits()) {
unsigned Type = L->getExtensionType();
if ((Type == ISD::ZEXTLOAD && C.ICmpType != SystemZICMP::SignedOnly) ||
(Type == ISD::SEXTLOAD && C.ICmpType != SystemZICMP::UnsignedOnly)) {
C.Op0 = C.Op0.getOperand(0);
C.Op1 = DAG.getConstant(0, C.Op0.getValueType());
}
}
}
}
// Return true if shift operation N has an in-range constant shift value.
// Store it in ShiftVal if so.
static bool isSimpleShift(SDValue N, unsigned &ShiftVal) {
@ -1541,6 +1562,7 @@ static Comparison getCmp(SelectionDAG &DAG, SDValue CmpOp0, SDValue CmpOp1,
if (C.Op0.getValueType().isFloatingPoint()) {
C.CCValid = SystemZ::CCMASK_FCMP;
C.Opcode = SystemZISD::FCMP;
adjustForFNeg(C);
} else {
C.CCValid = SystemZ::CCMASK_ICMP;
C.Opcode = SystemZISD::ICMP;
@ -1561,6 +1583,8 @@ static Comparison getCmp(SelectionDAG &DAG, SDValue CmpOp0, SDValue CmpOp1,
adjustZeroCmp(DAG, C);
adjustSubwordCmp(DAG, C);
adjustForSubtraction(DAG, C);
adjustForLTGFR(C);
adjustICmpTruncate(DAG, C);
}
if (shouldSwapCmpOperands(C)) {
@ -1569,8 +1593,6 @@ static Comparison getCmp(SelectionDAG &DAG, SDValue CmpOp0, SDValue CmpOp1,
}
adjustForTestUnderMask(DAG, C);
adjustForFNeg(C);
adjustForLTGFR(C);
return C;
}

22
test/CodeGen/SystemZ/int-cmp-44.ll
View File

@ -865,3 +865,25 @@ store:
exit:
ret i32 %res
}
; A version of f32 that tests the unextended value.
define i64 @f42(i64 %base, i64 %index, i64 *%dest) {
; CHECK-LABEL: f42:
; CHECK: ltgf %r2, 0({{%r2,%r3|%r3,%r2}})
; CHECK-NEXT: jh .L{{.*}}
; CHECK: br %r14
entry:
%add = add i64 %base, %index
%ptr = inttoptr i64 %add to i32 *
%val = load i32 *%ptr
%res = sext i32 %val to i64
%cmp = icmp sgt i32 %val, 0
br i1 %cmp, label %exit, label %store
store:
store i64 %res, i64 *%dest
br label %exit
exit:
ret i64 %res
}