middle-end/10472: [3.4 regression] ICE in instantiate_virtual_regs_lossage

[Kaveh R. Ghazi]

(Disclaimer: my remote x86 box is down today, everything done with
cross-compilers on sparc.)

I took a look at PR10472.


First I tried to determine under what circumstances and platforms the
bug appears.  While the PR was opened against cygwin, it seems it
should occur on any x86 target.  I'm guessing the reason we probably
haven't seen breakage on e.g. x86-linux-gnu (and why I'm not being
chased with torches and pitchforks) is that those targets use the
system gettext and don't compile the intl directory where the
triggering code lies.

But one should be able to trigger a bootstrap failure on linux-gnu if
configured using --with-included-gettext.


Second, I tried to see if I could reproduce it anywhere else.
I.e. what was unique about x86?  The cmpstr pattern could be playing a
part, so I built cross-compilers to s390-linux-gnu and i370-linux-gnu
(both of which have cmpstr) but they compile the testcase fine.

BTW, IMHO the reduced testcase in the PR is slightly misleading.  It
lead me at least to believe the bug had something to do with null
pointers.  A better snippet is something like this:

 > extern void f (char *);
 > void foo (char *s)
 > {
 >   f (__builtin_stpcpy (s, "hi"));
 > }

I.e. the problem only seems to occur when stpcpy or mempcpy are
themselves passed as a function call parameter.  The function called
does not have to be another builtin, it can be a regular call as shown
above.  When you call the stpcpy/mempcpy builtins in other contexts,
(standalone, in assignments, or in `if' statements) they work fine on
x86.

Both the testcase in the PR, and my reduced testcase above, pass
compilation on sparc, i370 and s390.  But we get a crash in cc1 on
x86.  I tried, but the root cause is beyond my abililty to figure out.
But I suspect something in the x86 backend.

Would someone please assist me in debugging this?

In the mean time, we can disable the optmization on x86 so that cygwin
people can resume bootstrap.  (Yes this is lame, sorry I'm not able to
provide a proper fix.)  We'll get testsuite failures in
execute/string-opt-18.c on x86 until this can be looked at by someone
more knowledgable that me.

Patch tested by building a cross-compiler to i686-pc-linux-gnu and
compiling the testcase in the PR as well as mine above.

Ok for mainline?

		Thanks,
		--Kaveh


2003-05-01  Kaveh R. Ghazi  <ghazi@caip.rutgers.edu>

	* builtins.c (expand_builtin_stpcpy): Disable on x86.
	(BUILT_IN_MEMPCPY): Likewise.

--- orig/egcc-CVS20030430/gcc/builtins.c	2003-04-28 10:00:20.000000000 -0400
+++ egcc-CVS20030430/gcc/builtins.c	2003-05-01 19:47:53.414417864 -0400
@@ -2487,6 +2487,9 @@ expand_builtin_stpcpy (arglist, target, 
      rtx target;
      enum machine_mode mode;
 {
+#ifdef TARGET_386 /* There are problems on x86, see PR 10472.  */
+  return 0;
+#else
   if (!validate_arglist (arglist, POINTER_TYPE, POINTER_TYPE, VOID_TYPE))
     return 0;
   else
@@ -2499,6 +2502,7 @@ expand_builtin_stpcpy (arglist, target, 
       chainon (arglist, build_tree_list (NULL_TREE, len));
       return expand_builtin_memcpy (arglist, target, mode, /*endp=*/2);
     }
+#endif
 }
 
 /* Callback routine for store_by_pieces.  Read GET_MODE_BITSIZE (MODE)
@@ -4621,9 +4625,11 @@ expand_builtin (exp, target, subtarget, 
       break;
 
     case BUILT_IN_MEMPCPY:
+#ifndef TARGET_386 /* There are problems on x86, see PR 10472.  */
       target = expand_builtin_memcpy (arglist, target, mode, /*endp=*/1);
       if (target)
 	return target;
+#endif
       break;
 
     case BUILT_IN_MEMMOVE: