[LLVMdev] New backend help request.

[James Boulton]

Hi all,

I'm trying to continue an existing m68k backend for LLVM. I'm completely new
to LLVM development so I've been muddling my way through mostly by trial and
error and using existing back ends for reference. I'm trying to implement
code to allow calling. I am compiling this C code --

typedef unsigned int uint32_t;
typedef char int8_t;

uint32_t foo(uint32_t x, int8_t y)
{
    return (x | (1 << 17)) + y;
}

int main()
{
	uint32_t b = foo(10,12);
}

And getting the following error from LLVM --

# Machine code for function main: Post SSA
Frame Objects:
  fi#0: size=4, align=4, at location [SP]
Function Live Outs: %D0L

BB#0: derived from LLVM BB %entry
        ADJCALLSTACKDOWN 6, %A7<imp-def>, %A7<imp-use>
        %vreg2<def> = COPY %A7; DR32:%vreg2
        %vreg1<def> = COPY %vreg2; AR:%vreg1 DR32:%vreg2
        MOVElim %vreg1<kill>, 0, 10; mem:ST4[<unknown>](align=2) AR:%vreg1
        %vreg2<def,tied1> = ADDlqd %vreg2<tied0>, 4, %CCR<imp-def,dead>;
DR32:%vreg2
        %vreg3<def> = COPY %vreg2; AR:%vreg3 DR32:%vreg2
        MOVEbim %vreg3<kill>, 0, 12; mem:ST1[<unknown>] AR:%vreg3
        CALL <ga:@foo>, %A7<imp-use>, ...
        ADJCALLSTACKUP 6, 0, %A7<imp-def>, %A7<imp-use>
        %vreg4<def> = COPY %D0L; DR32:%vreg4
        MOVEldm <fi#0>, 0, %vreg4<kill>; mem:ST4[%b] DR32:%vreg4
        %vreg5<def> = MOVEQ 0; DR32:%vreg5
        %D0L<def> = COPY %vreg5<kill>; DR32:%vreg5
        RTS %D0L<imp-use,kill>

# End machine code for function main.

*** Bad machine code: Using an undefined physical register ***
- function:    main
- basic block: BB#0 entry (0xa19eac)
- instruction: %vreg4<def> = COPY %D0L; DR32:%vreg4
- operand 1:   %D0L
LLVM ERROR: Found 1 machine code errors.
Stack dump:
0.      Program arguments:
D:\RetroMods\Jaguar\Compiler\llvm-build\bin\Debug\llc
.exe -mtriple m68k-apple-mac test.ll
1.      Running pass 'Function Pass Manager' on module 'test.ll'.
2.      Running pass 'Greedy Register Allocator' on function '@main'

To me this looks like the result from the call (D0) is not being set
somewhere to let LLVM know the register is available when it tries to copy
it into the virtual register. I'm using the MSP430 target as reference, and
I'm doing everything this target is, so I'm not sure what I'm missing.

Any tips would be most appreciated.