[Bug driver/63837] [5 Regression] r217391 causes kernel build errors with GCC_COMPARE_DEBUG=1

[manu at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63837

--- Comment #6 from Manuel López-Ibáñez <manu at gcc dot gnu.org> ---
Thanks for the testcase. It seems that the GCC_COMPARE_DEBUG=0 uses a temporary
file 

 ./cc1 -quiet -iprefix
/home/manuel/test1/217394M/build/gcc/../lib/gcc/x86_64-unknown-linux-gnu/5.0.0/
-isystem ./include -isystem ./include-fixed /dev/null -quiet -dumpbase null
"-mtune=generic" "-march=x86-64" -auxbase null -Wpointer-sign
"-fcompare-debug=-gtoggle" "-frandom-seed=0x6daada6b94b95048"
"-fdump-final-insns=/tmp/cc3xSGvK.gkd" -o /tmp/cc3L00jg.s

but the GCC_COMPARE_DEBUG=1 uses /dev/null:

 ./cc1 -quiet -iprefix
/home/manuel/test1/217394M/build/gcc/../lib/gcc/x86_64-unknown-linux-gnu/5.0.0/
-isystem ./include -isystem ./include-fixed /dev/null -quiet -dumpbase null.gk
"-mtune=generic" "-march=x86-64" -auxbase null -gtoggle -Wpointer-sign -w
"-fcompare-debug=-gtoggle" -fcompare-debug-second -o /dev/null
"-frandom-seed=0x6daada6b94b95048" "-fdump-final-insns=/tmp/ccMDEp8L.gk.gkd"

which triggers the heuristic. I can simply ignore /dev/null when checking for
input==output. I'm testing this patch:

Index: gcc.c
===================================================================
--- gcc.c       (revision 217457)
+++ gcc.c       (working copy)
@@ -4047,11 +4047,12 @@ process_command (unsigned int decoded_op
       read_cmdline_option (&global_options, &global_options_set,
                           decoded_options + j, UNKNOWN_LOCATION,
                           CL_DRIVER, &handlers, global_dc);
     }

-  if (output_file && strcmp (output_file, "-"))
+  if (output_file && strcmp (output_file, "-")
+      && strcmp (output_file, HOST_BIT_BUCKET))
     {
       int i;
       for (i = 0; i < n_infiles; i++)
        if ((!infiles[i].language || infiles[i].language[0] != '*')
            && canonical_filename_eq (infiles[i].name, output_file))
Index: toplev.c
===================================================================
--- toplev.c    (revision 217457)
+++ toplev.c    (working copy)
@@ -940,11 +940,12 @@ init_asm_output (const char *name)
          strcat (dumpname, ".s");
          asm_file_name = dumpname;
        }
       if (!strcmp (asm_file_name, "-"))
        asm_out_file = stdout;
-      else if (!canonical_filename_eq (asm_file_name, name))
+      else if (!canonical_filename_eq (asm_file_name, name)
+              || !strcmp (asm_file_name, HOST_BIT_BUCKET))
        asm_out_file = fopen (asm_file_name, "w");
       else
        /* Use fatal_error (UNKOWN_LOCATION) instead of just fatal_error to
           prevent gcc from printing the first line in the current file. */
        fatal_error (UNKNOWN_LOCATION,

If you can test it on your side, it would be helpful.