[gcc r17-3368] testsuite: do not leave a truncated summary behind

https://gcc.gnu.org/g:655d60b569339be88665ef5c6dcb1c01d5cbda39

commit r17-3368-g655d60b569339be88665ef5c6dcb1c01d5cbda39
Author: Kyrylo Tkachov <[email protected]>
Date:   Thu Aug 13 17:38:39 2026 +0200

    testsuite: do not leave a truncated summary behind
    
    The parallel check targets merge the per-instance summaries with
    
      dg-extract-results.sh $sums > $(TESTSUITEDIR)/$*/$*.sum
    
    which has two problems.  The redirection truncates the summary before the
    merge runs, so if the merge fails the tree is left with an empty one.  And
    the exit status is not looked at, so make check still succeeds.
    
    The merge fails exactly when a runtest instance did not write a summary,
    because the loop above names that file to the merge regardless.  An instance
    that died therefore does not just lose its own results, it discards the
    results of every other instance too, and reports success while doing it.
    
    Merge only from the instances that produced a summary, say plainly which ones
    did not, and build the merged files under a temporary name so that a failure
    leaves the previous ones alone.  A failed merge is now an error.
    
    The warning matters on its own: losing an instance silently loses a slice of
    the testsuite from the summary that comparisons are run against, and nothing
    in the output says so.
    
    Bootstrapped on aarch64-none-linux-gnu.
    
    gcc/ChangeLog:
    
            * Makefile.in ($(lang_checks_parallelized)): Only merge summaries
            from instances that produced one, and warn about the others.  Write
            the merged files through a temporary and fail if the merge fails.
    
    Signed-off-by: Kyrylo Tkachov <[email protected]>

Diff:
---
 gcc/Makefile.in | 19 ++++++++++++++-----
 1 file changed, 14 insertions(+), 5 deletions(-)

diff --git a/gcc/Makefile.in b/gcc/Makefile.in
index ce5894767fea..5c7cb98d22b0 100644
--- a/gcc/Makefile.in
+++ b/gcc/Makefile.in
@@ -4794,19 +4794,28 @@ $(lang_checks_parallelized): check-% : site.exp
 	    EXPECT=$(EXPECT) \
 	    check-parallel-$* \
 	    $(patsubst %,check-parallel-$*_%, $(check_p_subdirs)); \
-	  sums= ; logs= ; \
+	  sums= ; logs= ; lost= ; \
 	  for dir in $(TESTSUITEDIR)/$* \
 		     $(patsubst %,$(TESTSUITEDIR)/$*%,$(check_p_subdirs));\
 	  do \
 	    if [ -d $$dir ]; then \
-	      mv -f $$dir/$*.sum $$dir/$*.sum.sep; mv -f $$dir/$*.log $$dir/$*.log.sep; \
-	      sums="$$sums $$dir/$*.sum.sep"; logs="$$logs $$dir/$*.log.sep"; \
+	      if [ -f $$dir/$*.sum ]; then \
+		mv -f $$dir/$*.sum $$dir/$*.sum.sep; mv -f $$dir/$*.log $$dir/$*.log.sep; \
+		sums="$$sums $$dir/$*.sum.sep"; logs="$$logs $$dir/$*.log.sep"; \
+	      else \
+		lost="$$lost $$dir"; \
+	      fi; \
 	    fi; \
 	  done; \
+	  if [ -n "$$lost" ]; then \
+	    echo "warning: $*: these runtest instances produced no results:$$lost" >&2; \
+	  fi; \
 	  $(SHELL) $(srcdir)/../contrib/dg-extract-results.sh $$sums \
-	    > $(TESTSUITEDIR)/$*/$*.sum; \
+	    > $(TESTSUITEDIR)/$*/$*.sum.tmp || exit 1; \
 	  $(SHELL) $(srcdir)/../contrib/dg-extract-results.sh -L $$logs \
-	    > $(TESTSUITEDIR)/$*/$*.log; \
+	    > $(TESTSUITEDIR)/$*/$*.log.tmp || exit 1; \
+	  mv -f $(TESTSUITEDIR)/$*/$*.sum.tmp $(TESTSUITEDIR)/$*/$*.sum; \
+	  mv -f $(TESTSUITEDIR)/$*/$*.log.tmp $(TESTSUITEDIR)/$*/$*.log; \
 	  rm -rf $(TESTSUITEDIR)/$*-parallel || true; \
 	else \
 	  $(MAKE) TESTSUITEDIR="$(TESTSUITEDIR)" RUNTESTFLAGS="$(RUNTESTFLAGS)" \