[LLVMdev] LLVM Backend for Z80. ADD -> replaced -> OR

Fan Dawei
2012-04-25T14:31:03Z

Hi Peter,

I think the problem is that you did not explicitly define stack alignment
in Z80TargetMachine.cpp

DataLayout("e-p:16:8:8-i8:8:8-i16:8:8-i32:8:8-n8")

Try to add S16 to the string if your stack is 2-byte aligned. Refer to
http://llvm.org/docs/LangRef.html#datalayout .

If it does not work, try to specify the layout in the input module using
target layout directive.

David

On Wed, Apr 25, 2012 at 4:57 PM, Peter Hanzel <hanzelpeter at gmail.com>
wrote:

> Hello.
>
> I am playing with LLVM and trying to make Z80 (Zilog Z80) backend.
> The source code is attached.
>
> I have succesfully made some simple test. But now I have problem with ADD
> instruction.
> The source C code is:
>
> typedef struct
> {
> unsigned char id1;
> unsigned char id2;
> unsigned char id3;
>
> } testS;
>
> void simple()
> {
> testS test;
> test.id1 = 0x40;
> test.id2 = 0x80;
> test.id3 = 0xc0;
> }
>
> It produces this LLVM IR:
>
> %struct.testS = type { i8, i8, i8 }
>
> define void @simple() nounwind {
> entry:
>  %test = alloca %struct.testS, align 1
>  %id1 = getelementptr inbounds %struct.testS* %test, i32 0, i32 0
>  store i8 64, i8* %id1, align 1
>  %id2 = getelementptr inbounds %struct.testS* %test, i32 0, i32 1
>  store i8 -128, i8* %id2, align 1
>  %id3 = getelementptr inbounds %struct.testS* %test, i32 0, i32 2
>  store i8 -64, i8* %id3, align 1
>  ret void
> }
>
> And with llc -filetype=asm -march=z80 a get this .s file:
>
> .file "simple4.bc"
> .text
> .globl simple
> .type simple, at function
> simple:                                 # @simple
> # BB#0:                                 # %entry
> ld HL, 8
> add HL,SP                        <--- problem line
> ld DE, 1
> ld BC, 2
> ld (SP+6), BC
> ld B, H
> ld C, L
> or BC, DE
> ld (SP+4), BC
> ld (HL),64
> ld D, H
> ld E, L
> ld BC, (SP+6)
> or DE, BC
> ld BC, (SP+4)
> ld H, B
> ld L, C
> ld (HL),-128
> ld H, D
> ld L, E
> ld (HL),-64
> $tmp0:
> .size simple, ($tmp0)-simple
>
>
> The problem is that llc replaces ADD instruction with OR.
>
> Without defining OR16 function, the .S is not generated and claims that it
> cannot select OR instruction.
> So I added OR16 (that's the or BC,DE piece of code).
>
> But problem is that I am using the first two lines:
>
> ld HL, 8
> add HL,SP
>
> For FrameIndex and the HL register will contain SP which is only two
> 2bytes aligned.
> So "OR with 1" will work, but for second assigned :OR with
2" will not
> work.
>
> I suspect that llc is assuming that HL will contain 8 (that's the
start)
> and or-ing 8 with 1 or with 2 is ok.
> But my HL has also added SP to it.
> This is how my ISD::FrameIndex instruction look like:
>
> def addHLdisp : Z80Instr<(outs HL16:$dst), (ins i16imm:$disp,
GPR16:$src),
> "ld $dst, $disp\n\tadd $dst,$src",
> [(set HL16:$dst, (add GPR16:$src, (i16 imm:$disp)))]>;
>
> So it say that HL16:$dst wich is only HL register, will be changed.
> I also tried to change it to
> <(outs HL16:$dst), (ins i16imm:$disp, SP16:$src),
>
> But the output is the same.
>
> Can someone tell me what I am doing wrong?
>
> Peter.
>
>
>
>
>
>
>
>
>
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