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If a target zero or sign extends the result of its setcc, allow folding of 

this into sign/zero extension instructions later.

On PPC, for example, this testcase:

%G = external global sbyte
implementation
void %test(int %X, int %Y) {
  %C = setlt int %X, %Y
  %D = cast bool %C to sbyte
  store sbyte %D, sbyte* %G
  ret void
}

Now codegens to:

        cmpw cr0, r3, r4
        li r3, 1
        li r4, 0
        blt .LBB_test_2 ;
.LBB_test_1:    ;
        or r3, r4, r4
.LBB_test_2:    ;
        addis r2, r2, ha16(L_G$non_lazy_ptr-"L00000$pb")
        lwz r2, lo16(L_G$non_lazy_ptr-"L00000$pb")(r2)
        stb r3, 0(r2)

instead of:

        cmpw cr0, r3, r4
        li r3, 1
        li r4, 0
        blt .LBB_test_2 ;
.LBB_test_1:    ;
        or r3, r4, r4
.LBB_test_2:    ;
***     rlwinm r3, r3, 0, 31, 31
        addis r2, r2, ha16(L_G$non_lazy_ptr-"L00000$pb")
        lwz r2, lo16(L_G$non_lazy_ptr-"L00000$pb")(r2)
        stb r3, 0(r2)

llvm-svn: 21148
This commit is contained in:
Chris Lattner 2005-04-07 19:43:53 +00:00
parent 532ac79122
commit b32d9318d2
1 changed files with 13 additions and 1 deletions
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14
llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
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@ -585,7 +585,7 @@ SDOperand SelectionDAG::getNode(unsigned Opcode, MVT::ValueType VT,
break;
case ISD::ZERO_EXTEND:
if (Operand.getValueType() == VT) return Operand; // noop extension
if (OpOpcode == ISD::ZERO_EXTEND)
if (OpOpcode == ISD::ZERO_EXTEND) // (zext (zext x)) -> (zext x)
return getNode(ISD::ZERO_EXTEND, VT, Operand.Val->getOperand(0));
break;
case ISD::TRUNCATE:
@ -1025,6 +1025,18 @@ SDOperand SelectionDAG::getNode(unsigned Opcode, MVT::ValueType VT,SDOperand N1,
return N1;
}
// If we are extending the result of a setcc, and we already know the
// contents of the top bits, eliminate the extension.
if (N1.getOpcode() == ISD::SETCC)
switch (TLI.getSetCCResultContents()) {
case TargetLowering::UndefinedSetCCResult: break;
case TargetLowering::ZeroOrOneSetCCResult:
if (Opcode == ISD::ZERO_EXTEND_INREG) return N1;
break;
case TargetLowering::ZeroOrNegativeOneSetCCResult:
if (Opcode == ISD::SIGN_EXTEND_INREG) return N1;
break;
}
break;
}