[PATCH] Track indirect calls for call site information in debug info.

[Pierre-Marie de Rodat]

Hello,

On PowerPC targets with -mlongcall, most subprogram calls are turned 
into indirect calls: the call target is read from a register even though 
it is compile-time known. This makes it difficult for machine code 
static analysis engines to recover the callee information. The attached 
patch is an attempt to help such engines, generating 
DW_AT_abstract_origin attributes for all DW_TAG_GNU_call_site we are 
interested in.

Here is how it works:

    1. At -O0, the var-tracking pass is disabled, so in order to get a 
NOTE_INSN_CALL_ARG_LOCATION for each call we are interested in, this 
patch creates a new "naive" var-tracking pass. When optimizing, the 
regular var-tracking pass does this job and this new pass is disabled.

    2. The DWARF back-end (dwarf2out.c) first registers this RTL note 
(in dwarf2out_var_location, already existing code) and extracts the 
corresponding callee function symbol reference (new code to add handling 
for the case we are interested in).

       There, the patch also relaxes assertions in gen_subprogram_die: 
yes, we can have both a compile-time known call target and an indirect 
call. Already existing code in gen_subprogram_die calls 
gen_call_site_die and takes care of generating the corresponding debug 
information.

Bootstrapped and regtested on x86_64-pc-linux-gnu and powerpc-linux-gnu: 
no regression. Ok for trunk? Thank you in advance for your feedback!

gcc/ChangeLog:

         * passes.def: Add a new pass: variable_tracking_no_opt.
         * rtl.h (variable_tracking_no_opt_main): New.
         * tree-pass.h (make_pass_variable_tracking_no_opt): New.
         * var-tracking.c (variable_tracking_no_opt_main,
         pass_data_variable_tracking_no_opt,
         pass_variable_tracking_no_opt,
         make_pass_variable_tracking_no_opt): New.  Implement the new
         pass which adds notes for indirect calls.
         * dwarf2out.c (dwarf2out_var_location): Set the symbol reference
         for calls whose target is compile-time known but that are
         indirect.
         (gen_subprogram_die): Handle such calls.

-- 
Pierre-Marie de Rodat

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