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Avoid forming a SELECT_CC in a type that the target doesn't

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support. This isn't immediately interesting, because Legalize
ends up lowering SELECT_CC if the target doesn't support it,
but this simplifies the process.

Also, if the SELECT_CC would be expanded in Legalize, it
can potentially end up with two copies of the condition
expression. By leaving it as SELECT+SETCC, the SELECT can be
expanded into two SELECTs that use a single SETCC.

The two comparisons are usually CSE'd, but depending on
when various expressions get legalized, the comparison
expression could involve calls to library functions, such
that the comparison expression may not be able to be CSE'd.
This will be needed by a future patch.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@77896 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Dan Gohman 2009-08-02 16:19:38 +00:00
parent 7267734c39
commit 4ea480499c
1 changed files with 2 additions and 1 deletions
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3
lib/CodeGen/SelectionDAG/DAGCombiner.cpp
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@ -2829,7 +2829,8 @@ SDValue DAGCombiner::visitSELECT(SDNode *N) {
// Check against MVT::Other for SELECT_CC, which is a workaround for targets
// having to say they don't support SELECT_CC on every type the DAG knows
// about, since there is no way to mark an opcode illegal at all value types
if (TLI.isOperationLegalOrCustom(ISD::SELECT_CC, MVT::Other))
if (TLI.isOperationLegalOrCustom(ISD::SELECT_CC, MVT::Other) &&
TLI.isOperationLegalOrCustom(ISD::SELECT_CC, VT))
return DAG.getNode(ISD::SELECT_CC, N->getDebugLoc(), VT,
N0.getOperand(0), N0.getOperand(1),
N1, N2, N0.getOperand(2));