[m-rev.] for review: work around gcc bug (?)

[Peter Wang]

Has anyone else seen this?  It's happened now on my laptop and on
neptune, both x86-64 machines with gcc 4.1.2.  Strange that it doesn't
happen on the nightly builds.  It would be better to work around the
problem in MR_COMPUTED_GOTO but I don't know how.


Branches: main

compiler/purity.m:
        Work around a segfault while purity checking invalid/purity/purity.m.
        It seems to be due to gcc 4.1.2 on x86-64 miscompiling the computed
        goto following the workaround at gcc -O1 and above.

Index: compiler/purity.m
===================================================================
RCS file: /home/mercury/mercury1/repository/mercury/compiler/purity.m,v
retrieving revision 1.116
diff -u -r1.116 purity.m
--- compiler/purity.m   30 Dec 2007 08:23:54 -0000      1.116
+++ compiler/purity.m   22 Jan 2008 05:20:27 -0000
@@ -313,7 +313,9 @@
     ),
     WorstPurity = Purity,
     perform_pred_purity_checks(!.PredInfo, Purity, DeclPurity,
-        PromisedPurity, PurityCheckResult),
+        PromisedPurity, PurityCheckResult0),
+    % XXX works around a problem with gcc 4.1.2 on x86_64 machines
+    PurityCheckResult = workaround_gcc_bug(PurityCheckResult0),
     (
         PurityCheckResult = inconsistent_promise,
         Spec = error_inconsistent_promise(ModuleInfo, !.PredInfo, PredId,
@@ -339,6 +341,11 @@
     ),
     !:Specs = PredSpecs ++ !.Specs.
 
+:- func workaround_gcc_bug(purity_check_result) = purity_check_result.
+:- pragma no_inline(workaround_gcc_bug/1).
+
+workaround_gcc_bug(X) = X.
+
 repuritycheck_proc(ModuleInfo, proc(_PredId, ProcId), !PredInfo) :-
     pred_info_get_procedures(!.PredInfo, Procs0),
     map.lookup(Procs0, ProcId, ProcInfo0),



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