[PR96230] some -dumpbase-ext fixes

The initial bug report was that compiling (-c) with -dumpbase ""
-dumpbase-ext .<ext> crashes the driver.

The verification of -dumpbase-ext against -dumpbase doesn't cover the
case in which -dumpbase activates backward-compatibility mode.

I added a test for that, and for -dumpbase-ext without -dumpbase,
trying to make it work in a sensible way, as if applied to the default
-dumpbase for each file.  It turned out that this made for too much
complexity in dealing with suffixes derived from input filenames, so I
gave that up and returned to discarding -dumpbase-ext as documented,
ending up with a change identical to that in the original bug report.

I also thought I caught an off-by-one error in the initial
verification, that caused dumpbase_ext to be discarded if it was
identical to the specified dumpbase, but that turned out to be
intentional as well, so I put in comments and a test to reflect it.

Finally, an earlier version of the newly-added tests used "$var.ext"
in an expected output list, which showed me the handling of string
expansion was incorrect.  Reworked the expr into an eval to make that
work, and, absent any reliance on post-eval adjustments to so-expanded
output names, I arranged for the adjustments to be skipped after eval.


Co-Authored-By: "Zhanghaijian (A)" <z.zhanghaijian@huawei.com>
for  gcc/ChangeLog

	PR driver/96230
	* gcc.c (process_command): Adjust and document conditions to
	reset dumpbase_ext.

for  gcc/testsuite/ChangeLog

	PR driver/96230
	* gcc.misc-tests/outputs.exp: Add tests with -dumpbase-ext,
	with identical -dumpbase, with -dumpbase "", and without any
	-dumpbase.
	(outest): Fix "" expansion in expected outputs, skip
	adjustments.

1 files changed, 13 insertions, 2 deletions

diff --git a/gcc/gcc.c b/gcc/gcc.c
index c0eb3c1..10bc988 100644
--- a/gcc/gcc.c
+++ b/gcc/gcc.c
@@ -4907,6 +4907,9 @@ process_command (unsigned int decoded_options_count,
       int lendb = strlen (dumpbase);
       int lendbx = strlen (dumpbase_ext);
 
+      /* -dumpbase-ext must be a suffix proper; discard it if it
+	  matches all of -dumpbase, as that would make for an empty
+	  basename.  */
       if (lendbx >= lendb
 	  || strcmp (dumpbase + lendb - lendbx, dumpbase_ext) != 0)
 	{
@@ -5083,10 +5086,18 @@ process_command (unsigned int decoded_options_count,
   /* Check that dumpbase_ext, if still present, still matches the end
      of dumpbase, if present, and drop it otherwise.  We only retained
      it above when dumpbase was absent to maybe use it to drop the
-     extension from output_name before combining it with dumpdir.  */
+     extension from output_name before combining it with dumpdir.  We
+     won't deal with -dumpbase-ext when -dumpbase is not explicitly
+     given, even if just to activate backward-compatible dumpbase:
+     dropping it on the floor is correct, expected and documented
+     behavior.  Attempting to deal with a -dumpbase-ext that might
+     match the end of some input filename, or of the combination of
+     the output basename with the suffix of the input filename,
+     possible with an intermediate .gk extension for -fcompare-debug,
+     is just calling for trouble.  */
   if (dumpbase_ext)
     {
-      if (!dumpbase)
+      if (!dumpbase || !*dumpbase)
 	{
 	  free (dumpbase_ext);
 	  dumpbase_ext = NULL;