Hi!

On Wed, 25 Feb 2015 18:00:54 +0100, Jakub Jelinek <jakub@redhat.com> wrote:
> On Wed, Feb 25, 2015 at 11:28:12AM +0100, Thomas Schwinge wrote:
> > Am I on the right track with my assumption that it is correct that
> > nvptx.c:nvptx_option_override is not invoked in the offloading code path,
> > so we'd need a new target hook (?) to consolidate/override the options in
> > this scenario?
> > 
> > 
> > Using this to forcefully disable -fvar-tracking (as done in
> > nvptx_option_override), should then allow me to drop the following
> > beautiful specimen of a patch (which I didn't commit anywhere, so far):
> 
> Supposedly you could just disable var-tracking for
> targetm.no_register_allocation case, or change that assert to
> allow pseudos for targetm.no_register_allocation?

Just changing the assert, or handling this configuration differently:

diff --git gcc/var-tracking.c gcc/var-tracking.c
index 9ec5d8b..e37dc19 100644
--- gcc/var-tracking.c
+++ gcc/var-tracking.c
@@ -5439,6 +5449,10 @@ use_type (rtx loc, struct count_use_info *cui, machine_mode *modep)
 
   if (REG_P (loc))
     {
+      if (targetm.no_register_allocation)
+	if (REGNO (loc) >= FIRST_PSEUDO_REGISTER)
+	  return MO_CLOBBER;
+
       gcc_assert (REGNO (loc) < FIRST_PSEUDO_REGISTER);
 
       if (loc == cfa_base_rtx)

... is not enough: by the looks of it, the var-tracking code is just not
prepared to see pseudo registers, for example:

    /* Structure holding the IN or OUT set for a basic block.  */
    typedef struct dataflow_set_def
    {
    [...]
      /* Attributes for registers (lists of attrs).  */
      attrs regs[FIRST_PSEUDO_REGISTER];
    [...]

..., which is asserted in several places (one of which we stumbled over;
I added more in the attached var-tracking-asserts.patch).  I tried
disabling it:

diff --git gcc/var-tracking.c gcc/var-tracking.c
index 9ec5d8b..e37dc19 100644
--- gcc/var-tracking.c
+++ gcc/var-tracking.c
@@ -10404,7 +10421,10 @@ public:
   /* opt_pass methods: */
   virtual bool gate (function *)
     {
-      return (flag_var_tracking && !targetm.delay_vartrack);
+      return (flag_var_tracking
+	      && !targetm.delay_vartrack
+	      /* This code is not prepared to handle pseudo registers.  */
+	      && !targetm.no_register_allocation);
     }
 
   virtual unsigned int execute (function *)

..., but then we run into:

    $ build-gcc/gcc/xgcc -Bbuild-gcc/gcc/ -Bbuild-gcc/x86_64-unknown-linux-gnu/lib{gomp,gfortran}/ -Bbuild-gcc/x86_64-unknown-linux-gnu/lib{gomp,gfortran}/.libs -Ibuild-gcc/x86_64-unknown-linux-gnu/lib{gomp,gfortran} -Isource-gcc/{include,lib{gomp,gfortran}} -Lbuild-gcc/x86_64-unknown-linux-gnu/lib{gomp,gfortran}/.libs -Wl,-rpath,"$PWD"/build-gcc/x86_64-unknown-linux-gnu/lib{gomp,gfortran}/.libs source-gcc/libgomp/testsuite/libgomp.fortran/examples-4/e.50.1.f90 -Wall -Wextra -O2 -fopenmp -lgfortran -g
    source-gcc/libgomp/testsuite/libgomp.fortran/examples-4/e.50.1.f90: In function '__e_50_1_mod_MOD_vec_mult._omp_fn.1':
    source-gcc/libgomp/testsuite/libgomp.fortran/examples-4/e.50.1.f90:31:0: internal compiler error: in get_insn_template, at final.c:2124
             p(i) = v1(i) * v2(i)
     ^
    0x6b3765 get_insn_template(int, rtx_def*)
            [...]/source-gcc/gcc/final.c:2124
    0x6b55de final_scan_insn(rtx_insn*, _IO_FILE*, int, int, int*)
            [...]/source-gcc/gcc/final.c:2986
    0x6b6bff final(rtx_insn*, _IO_FILE*, int)
            [...]/source-gcc/gcc/final.c:2089
    0x6b76e9 rest_of_handle_final
            [...]/source-gcc/gcc/final.c:4488
    0x6b76e9 execute
            [...]/source-gcc/gcc/final.c:4563
    [...]
    mkoffload: fatal error: build-gcc/gcc/x86_64-unknown-linux-gnu-accel-nvptx-none-gcc returned 1 exit status
    [...]

Is this not the right way to skip it, or, Bernd, is this because we're
not yet handling some debug stuff in nvptx?  (I tested that
<http://news.gmane.org/find-root.php?message_id=%3C5466473A.1090809%40codesourcery.com%3E>
does not help with that.)  The following does make it work (that is,
resolve the ICEs), but that feels a bit too much ;-) of a hack:

--- gcc/var-tracking.c
+++ gcc/var-tracking.c
@@ -10305,7 +10322,8 @@ variable_tracking_main_1 (void)
 {
   bool success;
 
-  if (flag_var_tracking_assignments < 0)
+  if (flag_var_tracking_assignments < 0
+      || targetm.no_register_allocation)
     {
       delete_debug_insns ();
       return 0;


> Anyway, if var-tracking is never useful for NVPTX, if you want to override
> it early, flag_var_tracking* options are Optimization options, thus you'd
> need a target hook similar to the one I've added today, but instead of
> TARGET_OPTION_NODE do something similar for OPTIMIZATION_NODE streaming.


Grüße,
 Thomas