<html><head><meta http-equiv="Content-Type" content="text/html charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class="">Hi Fraser,<div class=""><br class=""></div><div class="">I think we want stick to being explicit about what the method does:</div><div class="">- No TRI, whole Reg</div><div class="">- TRI, Reg or super Reg</div><div class="">I.e., no magic aliases check unless we asked for.</div><div class=""><br class=""></div><div class="">You are right that we miss the any part of Reg option here. If adding an Overlap flag like we have for the Defs works for you, I would say, that’s the way to go.</div><div class=""><br class=""></div><div class="">I am surprised we didn’t need it sooner.</div><div class=""><br class=""></div><div class="">Cheers,</div><div class="">-Quentin<br class=""><div><blockquote type="cite" class=""><div class="">On Oct 4, 2016, at 4:00 AM, Fraser Cormack via llvm-dev <<a href="mailto:llvm-dev@lists.llvm.org" class="">llvm-dev@lists.llvm.org</a>> wrote:</div><br class="Apple-interchange-newline"><div class="">
<meta http-equiv="content-type" content="text/html; charset=utf-8" class="">
<div bgcolor="#FFFFFF" text="#000000" class="">
Hi,<br class="">
<br class="">
I was wondering what MachineInstr::findRegisterUseOperandIdx
"means". I have a situation where an instruction writes R0 and
another reads R0lo - the lower half of R0. Using
Use::findRegisterUseOperandIdx(R0) returns -1, because it only
checks against exact matches and "is-Reg-a-subreg-of-MOReg"
matches, of which neither are true.<br class="">
<br class="">
However, the instruction reads _part_ of R0, so should it return
true? It's really a question of semantics, as either:<br class="">
<br class="">
1) findRegisterUseOperandIdx returns the index if the instruction
reads the <i class="">whole</i> of Reg, or<br class="">
2) findRegisterUseOperandIdx returns the index if the instruction
reads <i class="">any part</i> of Reg<br class="">
<br class="">
If it's 2) then it appears as if there's a bug in there. If it's 1)
by design, then it doesn't seem to me as though there's a convenient
way of doing 2).<br class="">
<br class="">
There is another option, namely:<br class="">
<br class="">
3) findRegisterUseOperandIdx can do 1) or 2), depending on a flag<br class="">
<br class="">
There's an "Overlap" parameter to
MachineInstr::findRegisterDefOperandIdx - would that do the trick,
and do we want to add it to findRegisterUseOperandIdx?<br class="">
<br class="">
What do people think?<br class="">
<br class="">
Cheers,<br class="">
Fraser<br class="">
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Fraser Cormack
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