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Add comments for wrapper node patterns in MipsInstrInfo.td.

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llvm-svn: 132717
This commit is contained in:
Akira Hatanaka 2011-06-07 18:00:14 +00:00
parent 478976c99b
commit fe54bb9de1
1 changed files with 10 additions and 1 deletions
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11
lib/Target/Mips/MipsInstrInfo.td
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@ -87,7 +87,16 @@ def MipsDivRem : SDNode<"MipsISD::DivRem", SDT_MipsDivRem,
def MipsDivRemU : SDNode<"MipsISD::DivRemU", SDT_MipsDivRem,
[SDNPOutGlue]>;
// wrapper node
// Target constant nodes that are not part of any isel patterns and remain
// unchanged can cause instructions with illegal operands to be emitted.
// Wrapper node patterns give the instruction selector a chance to replace
// target constant nodes that would otherwise remain unchanged with ADDiu
// nodes. Without these wrapper node patterns, the following conditional move
// instrucion is emitted when function cmov2 in test/CodeGen/Mips/cmov.ll is
// compiled:
// movn %got(d)($gp), %got(c)($gp), $4
// This instruction is illegal since movn can take only register operands.
def MipsWrapperPIC : SDNode<"MipsISD::WrapperPIC", SDTIntUnaryOp>;
//===----------------------------------------------------------------------===//