[gcc r12-5405] Do not abort compilation when dump file is /dev/*

[gcc r12-5405] Do not abort compilation when dump file is /dev/*

[Giuliano Belinassi]

https://gcc.gnu.org/g:c7381debe4c5dd7878338f38db98face1cfa6f90

commit r12-5405-gc7381debe4c5dd7878338f38db98face1cfa6f90
Author: Giuliano Belinassi <gbelinassi@suse.de>
Date:   Tue Nov 16 13:25:32 2021 -0300

    Do not abort compilation when dump file is /dev/*
    
    The `configure` scripts generated with autoconf often tests compiler
    features by setting output to `/dev/null`, which then sets the dump
    folder as being /dev/* and the compilation halts with an error because
    GCC cannot create files in /dev/. This is a problem when configure is
    testing for compiler features because it cannot tell if the failure was
    due to unsupported features or any other problem, and disable it even
    if it is working.
    
    As an example, running configure overriding CFLAGS="-fdump-ipa-clones"
    will result in several compiler-features as being disabled because of
    gcc halting with an error creating files in /dev/*.
    
    This commit fixes this issue by checking if the output file is
    /dev/null or /dev/zero. In this case we use the current working
    directory for dump output instead of the directory of the output
    file because we cannot write to /dev/*.
    
    gcc/ChangeLog
    2021-11-16  Giuliano Belinassi  <gbelinassi@suse.de>
    
            * gcc.c (process_command): Skip dumpdir override if file is a
            not_actual_file_p.
            * doc/invoke.texi: Update -dumpdir documentation.
    
    gcc/testsuite/ChangeLog
    2021-11-16  Giuliano Belinassi  <gbelinassi@suse.de>
    
            * gcc.dg/devnull-dump.c: New.
    
    Signed-off-by: Giuliano Belinassi <gbelinassi@suse.de>

Diff:
---
 gcc/doc/invoke.texi                 | 3 ++-
 gcc/gcc.c                           | 3 ++-
 gcc/testsuite/gcc.dg/devnull-dump.c | 7 +++++++
 3 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index 1b02ea09197..49c8befd58a 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -1880,7 +1880,8 @@ named @file{dir/bar.*}, combining the given @var{dumppfx} with the
 default @var{dumpbase} derived from the primary output name.  Dump
 outputs also take the input name suffix: @file{dir/bar.c.*}.
 
-It defaults to the location of the output file; options
+It defaults to the location of the output file, unless the output
+file is a special file like @code{/dev/null}. Options
 @option{-save-temps=cwd} and @option{-save-temps=obj} override this
 default, just like an explicit @option{-dumpdir} option.  In case
 multiple such options are given, the last one prevails:
diff --git a/gcc/gcc.c b/gcc/gcc.c
index 506c2acc282..6ff22781042 100644
--- a/gcc/gcc.c
+++ b/gcc/gcc.c
@@ -5098,7 +5098,8 @@ process_command (unsigned int decoded_options_count,
 
   bool explicit_dumpdir = dumpdir;
 
-  if (!save_temps_overrides_dumpdir && explicit_dumpdir)
+  if ((!save_temps_overrides_dumpdir && explicit_dumpdir)
+      || (output_file && not_actual_file_p (output_file)))
     {
       /* Do nothing.  */
     }
diff --git a/gcc/testsuite/gcc.dg/devnull-dump.c b/gcc/testsuite/gcc.dg/devnull-dump.c
new file mode 100644
index 00000000000..378e0901c28
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/devnull-dump.c
@@ -0,0 +1,7 @@
+/* { dg-do assemble } */
+/* { dg-options "-fdump-ipa-clones -o /dev/null" } */
+
+int main()
+{
+  return 0;
+}