[Bug middle-end/18089] [4.0 regression] Valgrind errors in real.c

jakub at gcc dot gnu dot org gcc-bugzilla@gcc.gnu.org
Fri Jan 14 18:35:00 GMT 2005


------- Additional Comments From jakub at gcc dot gnu dot org  2005-01-14 18:35 -------
Are you sure this is not just a bug in valgrind?
I have verified that with current CVS I get
ERROR SUMMARY: 37 errors from 21 contexts (suppressed: 12 from 1)
while if I rebuild stage1's combine.o with Roger's patch backed out, link new
stage1 cc1, then rebuild stage2's real.o with the new stage1 cc1 and link new
stage2 cc1, I get
ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 12 from 1)

I did a binary search on real.s and e.g. one of the valgrind errors is triggered
by following change in real.s:
@@ -6453,8 +6453,8 @@ round_for_format:
        .p2align 2,,3
 .L997:
        movl    (%ebp), %eax
+       subl    $-2147483648, %eax
        shrl    $5, %eax
-       xorl    $67108864, %eax
        subl    $67108864, %eax
        cmpl    %eax, 32(%esp)
        jge     .L979

With the xorl there are no errors, with subl there is one error.
But I don't see any functional difference between these two.
If I replace 28 occurences of these subl $0x80000000, %eax before >> 5 to
xorl $0x4000000, %eax after >> 5 (I left out encoders/decoders of non-ieee
formats), valgrind stops reporting any errors.

So to me this looks like valgrind not handling subl $0x80000000, %eax
instruction correctly.

Do you agree?

I used valgrind 2.2.0.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jakub at redhat dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18089



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