Add comments for wrapper node patterns in MipsInstrInfo.td.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@132717 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Akira Hatanaka 2011-06-07 18:00:14 +00:00
parent be234dabf4
commit 6cd4b4e657

View File

@ -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>;
//===----------------------------------------------------------------------===//