llvm dev - Jul 2012 - [LLVMdev] Issue with Machine Verifier and earlyclobber

On Jul 15, 2012, at 9:20 AM, Borja Ferrer <borja.ferav at gmail.com>
wrote:
> Jakob, one more hint, I've placed some asserts around the code you
added and noticed that the InlineSpiller::insertReload() function is not being
called.
> 
> 2012/7/14 Borja Ferrer <borja.ferav at gmail.com>
> Hello Jakob,
> 
> I'm still getting the error, I can give you any other debug info you
need. I haven't pasted the regalloc debug info here because it is quite
huge, but if you tell me what specific details you need I will include them.
Sorry, I can't debug this for you. I suggest you take a look at the code
yourself.

/jakob

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I think I'm getting a bit closer to the problem. I've found that the
call
to InlineSpiller::foldMemoryOperand() inside
InlineSpiller::spillAroundUses() is causing the problems.
As a test, I removed that call and with your yesterday's patch I'm not
getting any errors at all, the code generated is the same one as with the
call. This is happening when InlineSpiller::foldMemoryOperand() returns
true, so a very wild guess is that maybe when calling
LIS.ReplaceMachineInstrInMaps() the new SlotIndex created is not of type
Slot_EarlyClobber since the MI being replaced is a COPY with no EC ops.

I've also found a way for you to reproduce this error in a simple way with
the ARM backend with -march=thumb:
Just add "Constraints = "@earlyclobber $Rt" in" to the
tLDRspi instruction
in ARMInstrThumb.td (around line 620) and compile the following code with
llc at -O3:

target datalayout
"e-p:32:32:32-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:32:64-f32:32:32-f64:32:64-v64:32:64-v128:32:128-a0:0:32-n32-S32"
target triple = "armv4t-generic-generic"
define float @f3(float %days) nounwind readnone {
entry:
  %mul = fmul float %days, 0x3FEF8A6C60000000
  %add = fadd float %mul, 0x40718776A0000000
  %mul1 = fmul float %days, 0x3FEF8A09A0000000
  %add2 = fadd float %mul1, 0x4076587740000000
  %mul3 = fmul float %days, 0x3E81B35CC0000000
  %sub = fsub float 0x3FFEA235C0000000, %mul3
  %call = tail call float @dsin(float %add2) nounwind readnone
  %mul4 = fmul float %sub, %call
  %mul5 = fmul float %days, 0x3E27C04CA0000000
  %sub6 = fsub float 0x3F94790B80000000, %mul5
  %mul7 = fmul float %add2, 2.000000e+00
  %call8 = tail call float @dsin(float %mul7) nounwind readnone
  %mul9 = fmul float %sub6, %call8
  %add10 = fadd float %mul4, %mul9
  %add11 = fadd float %add, %add10
  %mul12 = fmul float %days, 0x3E13C5B640000000
  %sub13 = fsub float 0x3F911C1180000000, %mul12
  %mul14 = fmul float %add, 2.000000e+00
  %call15 = tail call float @dsin(float %mul14) nounwind readnone
  %mul16 = fmul float %call15, 0x3FF1F736C0000000
  %mul17 = fmul float %sub13, 2.000000e+00
  %mul19 = fmul float %mul17, %call
  %sub20 = fsub float %mul16, %mul19
  %mul21 = fmul float %sub13, 4.000000e+00
  %mul22 = fmul float %mul21, 0x3FF1F736C0000000
  %mul24 = fmul float %mul22, %call
  %call26 = tail call float @dcos(float %mul14) nounwind readnone
  %mul27 = fmul float %mul24, %call26
  %add28 = fadd float %sub20, %mul27
  %call29 = tail call float @dsin(float %add11) nounwind readnone
  %mul30 = fmul float %call29, 0x3FF0AB6960000000
  %call31 = tail call float @dasin(float %mul30) nounwind readnone
  %add32 = fadd float %call31, %add28
  ret float %add32
}

declare float @dsin(float) nounwind readnone
declare float @dcos(float) nounwind readnone
declare float @dasin(float) nounwind readnone

You will get the following error:

*** Bad machine code: No live range at def ***
- function:    f3
- basic block: entry 0x9e5d2bc (BB#0) [0B;3360B)
- instruction: 2440e    %vreg51<earlyclobber,def> = tLDRspi <fi#0>,
0,
pred:14, pred:%noreg; mem:LD4[FixedStack0] tGPR:%vreg51
- operand 0:   %vreg51<earlyclobber,def>
2440e is not live in [2440r,2976r:0)  0 at 2440r

*** Bad machine code: Early clobber def must be at an early-clobber slot ***
- function:    f3
Valno #0 is defined at 2440r in [2440r,2976r:0)  0 at 2440r2440r
LLVM ERROR: Found 2 machine code errors.

Hope this helps a bit.

Thanks!
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On Jul 15, 2012, at 4:50 PM, Borja Ferrer <borja.ferav at gmail.com>
wrote:
> I think I'm getting a bit closer to the problem. I've found that
the call to InlineSpiller::foldMemoryOperand() inside
InlineSpiller::spillAroundUses() is causing the problems.
> As a test, I removed that call and with your yesterday's patch I'm
not getting any errors at all, the code generated is the same one as with the
call. This is happening when InlineSpiller::foldMemoryOperand() returns true, so
a very wild guess is that maybe when calling LIS.ReplaceMachineInstrInMaps() the
new SlotIndex created is not of type Slot_EarlyClobber since the MI being
replaced is a COPY with no EC ops.
OK, I see what is happening. We don't expect foldMemoryOperand to turn a
normal def into an early-clobber and vice versa.

This is not easy to fix, could you file a PR, please?

As a workaround, you can use a pseudo-instruction in loadRegFromStackSlot() that
doesn't have the early-clobber flag. Then replace it with the real
instruction in expandPostRAPseudo().

/jakob