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Admonish that MI is not IR and virtual registers have constraints.

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In machine code, you can't just replaceRegWith() the same way you can
replaceAllUsesWith() in IR.  Virtual registers may have different
register classes that need to be merged first.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@142201 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Jakob Stoklund Olesen 2011-10-17 17:33:39 +00:00
parent 827454e6e2
commit 4007529d4b
1 changed files with 8 additions and 0 deletions
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8
include/llvm/CodeGen/MachineRegisterInfo.h
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@ -171,6 +171,14 @@ public:
/// replaceRegWith - Replace all instances of FromReg with ToReg in the
/// machine function. This is like llvm-level X->replaceAllUsesWith(Y),
/// except that it also changes any definitions of the register as well.
///
/// Note that it is usually necessary to first constrain ToReg's register
/// class to match the FromReg constraints using:
///
/// constrainRegClass(ToReg, getRegClass(FromReg))
///
/// That function will return NULL if the virtual registers have incompatible
/// constraints.
void replaceRegWith(unsigned FromReg, unsigned ToReg);
/// getRegUseDefListHead - Return the head pointer for the register use/def