[PATCH] D78137: [RegBankSelect] Hide assertion failure from LLT::getScalarSizeInBits

Tue Apr 14 17:25:45 PDT 2020

vsk added a comment.

In D78137#1982359 <https://reviews.llvm.org/D78137#1982359>, @dsanders wrote:

> > (lldb) p MF.dump()
> > 
> > 1. Machine code for function phiPropagation: IsSSA, TracksLiveness, Legalized
> > 
> >   bb.0.entry: successors: %bb.2(0x40000000), %bb.1(0x40000000); %bb.2(50.00%), %bb.1(50.00%) liveins: $x0, $x1, $w2 %0:gpr32 = LDRWui killed $x0, 0, debug-location !23 :: (load 4 from %ir.src); /Users/vsk/src/llvm-project-master/llvm/test/CodeGen/AArch64/GlobalISel/arm64-regbankselect.mir:6:1 DBG_VALUE %0:gpr32, $noreg, !"1", !DIExpression(), debug-location !23; /Users/vsk/src/llvm-project-master/llvm/test/CodeGen/AArch64/GlobalISel/arm64-regbankselect.mir:6:1 line no:6 ```
>
> If you moved the DBG_VALUE below the `%5(s32) = COPY %0` does it still assert? It's interesting that the target instruction means the DBG_VALUE is the first to be processed in that def/use chain but I suspect the real problem is that it's not deriving the register bank from the register class and the special case for COPY deals with that.

No, after moving the DBG_VALUE, I don't hit the assertion:

  %0:gpr32 = LDRWui
  %5:_(s32) = COPY %0
  DBG_VALUE %5

Sorry, I'm not entirely sure what to make of that. Do you suspect -mir-debugify is adding DBG_VALUE insts in the wrong place? In the generic regbankselect path, is it required for operands to go through a COPY before they can be used?

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https://reviews.llvm.org/D78137