[LLVMdev] Tracing nodes in selectionDAG to final code...

[Arnold Schwaighofer]

What Krzysztof said and you might want to look at
lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp to see when the various
stages happen during ISel (SelectionDAGISel::CodeGenAndEmitDAG()).

There are also the various -view-<some>-dag flags that you can use
with llc if you have dotty or graphviz installed to watch instruction
lowering happening in a more graphical manner.

See also http://llvm.org/docs/CodeGenerator.html#instruction-selection-section.

For code and instruction lowering description specific to MIPS look in
lib/Target/Mips/Mips-ISelLowering.cpp, -InstrInfo.td, and
-ISelDAGToDAG.cpp.

On Sun, Nov 11, 2012 at 6:41 AM, Joseph Reddington <joseph at cs.rhul.ac.uk> wrote:
> Hello everyone.
>
> I use this command
>
> clang -emit-llvm hello.c -c -o hello.bc
> llc hello.bc -march=mipsel -relocation-model=static -o hello.s
>
> to produce this MIPS code:
>
> .section .mdebug.abi32
> .previous
> .file "hello.bc"
> .text
> .globl main
> .align 2
> .type main, at function
> .set nomips16                # @main
> .ent main
> main:
> .cfi_startproc
> .frame $sp,32,$ra
> .mask 0x80000000,-4
> .fmask 0x00000000,0
> .set noreorder
> .set nomacro
> # BB#0:                                 # %entry
> addiu $sp, $sp, -32
> $tmp2:
> .cfi_def_cfa_offset 32
> sw $ra, 28($sp)            # 4-byte Folded Spill
> $tmp3:
> .cfi_offset 31, -4
> lui $2, %hi(__gnu_local_gp)
> addiu $2, $2, %lo(__gnu_local_gp)
> sw $2, 16($sp)
> sw $zero, 24($sp)
> lui $2, %hi($.str)
> addiu $4, $2, %lo($.str)
> jal printf
> nop
> addiu $2, $zero, 0
> lw $ra, 28($sp)            # 4-byte Folded Reload
> addiu $sp, $sp, 32
> jr $ra
> nop
> .set macro
> .set reorder
> .end main
> $tmp4:
> .size main, ($tmp4)-main
> .cfi_endproc
>
> .type $.str, at object           # @.str
> .section .rodata.str1.1,"aMS", at progbits,1
> $.str:
> .asciz "hello world\n"
> .size $.str, 13
>
>
>
> from a simple hello world example that looks like:
>
>
> #include <stdio.h>
>
> int main() {
>  printf("hello world\n");
>    return 0;
> }
>
>
> I use the method I talked about at
> (http://markmail.org/message/3micyhqjpgx7fwvv) to itterate over the
> nodes in the selectionDAG, the operations are effectively...
>
> -Operation EntryToken has number 0
> -Operation Constant has number 1
> -Operation FrameIndex has number 2
> -Operation undef has number 3
> -Operation store has number 4
> -Operation GlobalAddress has number 5
> -Operation GlobalAddress has number 6
> -Operation TargetConstant has number 7
> -Operation callseq_start has number 8
> -Operation TargetGlobalAddress has number 9
> -Operation Register has number 10
> -Operation CopyToReg has number 11
> -Operation RegisterMask has number 12
> -Operation MipsISD::JmpLink has number 13
> -Operation TargetConstant has number 14
> -Operation TargetConstant has number 15
> -Operation callseq_end has number 16
> -Operation Register has number 17
> -Operation CopyFromReg has number 18
> -Operation CopyToReg has number 19
> -Operation Register has number 20
> -Operation MipsISD::Ret has number 21
>
> What I'd like to know now is how I might tell which parts of MIPS each
> operation in the selectionDAG produced?  I'm pressuming there is a
> specification in the filesystem somewhere and it would be great to get
> a pointer...
>
> Thanks
>
> Joe
>
>
>
>
>
> --
> Dr Joseph Reddington
> Computer Science, Royal Holloway
> For 2012 I have a resolution to write all my email responses within
> 24-hours - no exceptions. If you've not had a response, there's been a
> misunderstanding somewhere, and it's worth reminding me.
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