[Bug c/57018] New: Miscompilation of bison 2.7.1 under "-Os -fomit-frame-pointer"

[michael at talamasca dot ocis.net]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57018



             Bug #: 57018

           Summary: Miscompilation of bison 2.7.1 under "-Os

                    -fomit-frame-pointer"

    Classification: Unclassified

           Product: gcc

           Version: 4.8.0

            Status: UNCONFIRMED

          Severity: normal

          Priority: P3

         Component: c

        AssignedTo: unassig...@gcc.gnu.org

        ReportedBy: mich...@talamasca.ocis.net





Created attachment 29906

  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=29906

Code to generate a pair of objects showing the bug



GCC 4.8.0 miscompiles bison 2.7.1 when compiling for space with frame pointer

omission.  (I've built gcc with --enable-frame-pointer expressly so my code

isn't bloated with exception data when I omit it on the command line.)



There are multiple breakages, but I've nailed down one of them in the attached

case.  It seems to involve the combination of passing structures by value and

the optimization opportunities of functions not called from outside an object.



So long as extenal_noop does nothing, calling real_entry_point should always

result in its argument being copied to main_blob.  But main_blob is full of

garbage at the problematic optimization "-Os -fomit-frame-pointer".



This is on i386-pc-linux-uclibc.