[LLVMdev] Problem in X86 backend

[Quentin Colombet]

Hi Julien,

> On Oct 28, 2014, at 2:14 AM, Rinaldini Julien <julien.rinaldini at heig-vd.ch> wrote:
> 
> Hum, in fact, I'm still a bit lost ;)
> 
> It seems to works in -O0, but in -O1, -O2 and -O3, I got this error (+ the dump of the function):
> 
> # Machine code for function foo: Post SSA
> Function Live Ins: %RDI in %vreg7
> 
> BB#0: derived from LLVM BB %entry
>    Live Ins: %RDI
>        %vreg7<def> = COPY %RDI; GR64:%vreg7
>        %vreg1<def> = MOV64rm %vreg7, 1, %noreg, 8, %noreg; mem:LD8[%args.03](tbaa=<badref>) GR64:%vreg1,%vreg7
>        TEST64rr %vreg1, %vreg1, %EFLAGS<imp-def>; GR64:%vreg1
>        JE_4 <BB#3>, %EFLAGS<imp-use,kill>
>    Successors according to CFG: BB#3(12) BB#1(20)
> 
> BB#1: 
>    Predecessors according to CFG: BB#0
>        %vreg9<def> = COPY %vreg1; GR64:%vreg9,%vreg1
>        %vreg10<def> = COPY %vreg7; GR64:%vreg10,%vreg7
>        %vreg0<def> = LEA64r %vreg7, 1, %noreg, 8, %noreg; GR64:%vreg0,%vreg7
>        %vreg11<def> = COPY %vreg0; GR64:%vreg11,%vreg0
>    Successors according to CFG: BB#2
> 
> BB#2: derived from LLVM BB %while.body
>    Predecessors according to CFG: BB#2 BB#1
>        %vreg4<def> = COPY %vreg11; GR64:%vreg4,%vreg11
>        %vreg3<def> = COPY %vreg10; GR64:%vreg3,%vreg10
>        %vreg2<def> = COPY %vreg9; GR64:%vreg2,%vreg9
>        ADJCALLSTACKDOWN64 0, %RSP<imp-def>, %EFLAGS<imp-def,dead>, %RSP<imp-use>
>        %RDI<def> = COPY %vreg2; GR64:%vreg2
>        CALL64pcrel32 <ga:@puts>, <regmask>, %RSP<imp-use>, %RDI<imp-use>, %RSP<imp-def>, ...
>        ADJCALLSTACKUP64 0, 0, %RSP<imp-def>, %EFLAGS<imp-def,dead>, %RSP<imp-use>
>        %vreg6<def> = MOV64rm %vreg3, 1, %noreg, 16, %noreg; mem:LD8[%args.0](tbaa=<badref>) GR64:%vreg6,%vreg3
>        %vreg5<def> = COPY %vreg3; GR64:%vreg5,%vreg3
>        %vreg5<def,tied1> = ADD64ri8 %vreg5<tied0>, 16, %EFLAGS<imp-def,dead>; GR64:%vreg5
>        TEST64rr %vreg6, %vreg6, %EFLAGS<imp-def>; GR64:%vreg6
>        %vreg9<def> = COPY %vreg6; GR64:%vreg9,%vreg6
>        %vreg10<def> = COPY %vreg4; GR64:%vreg10,%vreg4
>        %vreg11<def> = COPY %vreg5; GR64:%vreg11,%vreg5
>        JNE_4 <BB#2>, %EFLAGS<imp-use,kill>
>        JMP_4 <BB#3>
>    Successors according to CFG: BB#3(4) BB#2(124)
> 
> BB#3: derived from LLVM BB %while.end
>    Predecessors according to CFG: BB#0 BB#2
>    Successors according to CFG: BB#4
> 
> BB#4: derived from LLVM BB %while.end
>    Predecessors according to CFG: BB#3 BB#5
>        CMP64rr %RDI, %RBP<kill>, %EFLAGS<imp-def>
>        JE_4 <BB#6>, %EFLAGS<imp-use,kill>
>    Successors according to CFG: BB#6 BB#5
> 
> BB#5: derived from LLVM BB %while.end
>    Predecessors according to CFG: BB#4
>        MOV32mi %RDI<kill>, 1, %noreg, 0, %noreg, 0

Your problem is that kill flag on RDI. Indeed, this is not the last use of RDI in your case and because you set this flag, when jumping to BB#4, the compiler thinks that RDI is not defined.

Also, I am not sure what you are trying to achieve, but are you sure you always want to use RDI? In this case, should it be vreg7 for instance?

-Quentin 

>        JMP_4 <BB#4>
>    Successors according to CFG: BB#4
> 
> BB#6: derived from LLVM BB %while.end
>    Predecessors according to CFG: BB#4
>        RETQ
> 
> # End machine code for function foo.
> 
> *** Bad machine code: Using an undefined physical register ***
> - function:    foo
> - basic block: BB#4 while.end (0x46c4840)
> - instruction: CMP64rr %RDI, %RBP<kill>, %EFLAGS<imp-def>
> - operand 0:   %RDI
> 
> *** Bad machine code: Using an undefined physical register ***
> - function:    foo
> - basic block: BB#4 while.end (0x46c4840)
> - instruction: CMP64rr %RDI, %RBP<kill>, %EFLAGS<imp-def>
> - operand 1:   %RBP<kill>
> 
> *** Bad machine code: Using an undefined physical register ***
> - function:    foo
> - basic block: BB#5 while.end (0x46c48f0)
> - instruction: MOV32mi %RDI<kill>, 1, %noreg, 0, %noreg, 0
> - operand 0:   %RDI<kill>
> 
> 
> Cheers
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