llvm dev - Jan 2019 - How to debug Before Expand ISel Pseudo-instructions ?

Hi,

I'm new to LLVM and I ran llc with -print-before-all and I can see that the
IR is already wrong before Expand ISel Pseudo-instructions. The MOVE instruction
moves a register to itself and shouldn't be there. How do you debug
something like this?

*** IR Dump After Module Verifier ***
define i32* @_Z9test_mathv() #0 {
  %a = alloca i32, align 4
  ret i32* %a
}
# *** IR Dump Before Expand ISel Pseudo-instructions ***:
# Machine code for function _Z9test_mathv: Properties: <>
Frame Objects:
  fi#0: size=4, align=4, at location [SP]

BB#0: derived from LLVM BB %0
        %vreg0<def> = MOVE %vreg0; CPURegs:%vreg0
        %R4<def> = COPY %vreg0; CPURegs:%vreg0
        JLR %R4




Thanks
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On 1/9/2019 3:23 PM, m m via llvm-dev wrote:
> Hi,
>
> I'm new to LLVM and I ran llc with -print-before-all and I can see 
> that the IR is already wrong before Expand ISel Pseudo-instructions. 
> The MOVE instruction moves a register to itself and shouldn't be 
> there. How do you debug something like this?

"-debug" dumps a lot of additional information.   More specifically, 
"-debug-only=isel" probably has the information you're looking
for.


-Eli

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