David, for completion I am updating this message with what I've learned. I
do this in the hope that I might assist the next poor souls that find
themselves reverse-engineering front ends because they are creating their
own front end.
I claim only that this worked for me. I can't you tell what assumptions
I've been making, because I don't know what I don't know.
That said: I found that for file-static variables, the trick is to create a
var_decl for the variable with TREE_STATIC(var_decl)=1, and then to call
rest_of_decl_compilation (var_decl, true, false); // top_level is true;
at_end is false
Having done that for an integer_type var_decl with the name
"dubner_at_work", and with an initial value of 123454321, I now see this at
the very beginning of the generated .s file:
######################
.file "call-scope-1.cbl"
.text
.Ltext0:
.file 0 "/home/bob/repos/gcc-cobol/gcc/cobol/failures/call-scope-1"
"call-scope-1.cbl"
.data
.align 4
.type dubner_at_work, @object
.size dubner_at_work, 4
dubner_at_work:
.long 123454321
.section .rodata [...]
######################
And that's exactly what I wanted.
Thanks for your help. It was your mention of "rest_of_compilation" that
ended this marathon investigation, and I really appreciate it.
Bob Dubner
-----Original Message-----
From: Gcc <[email protected]> On Behalf Of Robert
Dubner
Sent: Monday, November 28, 2022 21:55
To: David Malcolm <[email protected]>; [email protected]
Cc: Bob Dubner <[email protected]>
Subject: RE: Code generation: How to define file-scope static variables?
David, thank you very much. That looks very much like what I was hoping
for.
I'll dig into it tomorrow.
Heartfelt thanks,
Bob Dubner.
-----Original Message-----
From: David Malcolm <[email protected]>
Sent: Monday, November 28, 2022 18:01
To: Robert Dubner <[email protected]>; [email protected]
Cc: 'Bob Dubner' <[email protected]>
Subject: Re: Code generation: How to define file-scope static variables?
On Mon, 2022-11-28 at 15:28 -0600, Robert Dubner wrote:
> I am part of a team working on a COBOL front end for GCC.
>
> By reverse engineering other front ends, I learned, some months ago,
> how to create a function_decl GENERIC node that is the root of a
> GENERIC tree describing an entire function.
>
> By calling the routine cgraph_node::finalize_function() with that
> function_decl, the assembly language for that function is created, and
> all is well.
>
> But now I need to be able to create the equivalent of a file-scope
> static variable in C.
>
> This C program file:
>
> //////////////////
> static int dubner_at_work = 123454321; int main(int argc, char **argv)
> {
> }
> //////////////////
>
> produces, in part, this assembly language:
>
> ###############
> .file "ccc.c"
> .text
> .data
> .align 4
> .type dubner_at_work, @object
> .size dubner_at_work, 4
> dubner_at_work:
> .long 123454321
> .text
> .globl main
> .type main, @function
> [...]
> ###############
>
> In my own GENERIC generation code, I believe that I am creating a
> proper translation_unit_decl that contains the block and the vars
> nodes for specifying "dubner_at_work".
>
> But I have been unable, after several days of looking, to figure out
> the equivalent of "cgraph_node::finalize_function" for a
> translation_unit_decl. The resulting assembly language doesn't have a
> definition for "dubner_at_work".
>
> Can anybody describe how I can tell the downstream processing that I
> need the translation_unit_decl to actually define storage?
You might find libgccjit's gcc/jit/jit-playback.cc helpful for this, as it
tends to contain minimal code to build trees (generally
simplified/reverse-engineered from the C frontend).
playback::context::global_new_decl makes the VAR_DECL node, and such trees
are added to the jit playback::context's m_globals. In
playback::context::replay, we have:
/* Finalize globals. See how FORTRAN 95 does it in gfc_be_parse_file()
for a simple reference. */
FOR_EACH_VEC_ELT (m_globals, i, global)
rest_of_decl_compilation (global, true, true);
wrapup_global_declarations (m_globals.address(), m_globals.length());
So you'll probably want to do something similar for your globals.
Caveat: this is all reverse-engineered by me/others from the C frontend (and
I haven't touched this code in a while), so I may be missing things here.
Dave
