public inbox for gcc-bugs@sourceware.org
help / color / mirror / Atom feed
* [Bug target/31830]  New: Input parameter trashed with optimization -O when using a union and bit field
@ 2007-05-04 23:38 gmorain at gmail dot com
  2007-05-04 23:47 ` [Bug target/31830] " gmorain at gmail dot com
                   ` (2 more replies)
  0 siblings, 3 replies; 5+ messages in thread
From: gmorain at gmail dot com @ 2007-05-04 23:38 UTC (permalink / raw)
  To: gcc-bugs

This occurs with a cross compilation from i386-linux to powerpc-elf.  The input
parameter in r3 gets overwritten by the return value from a function call. 
This only occurs when optimization is enabled (-O1 or higher).  This has
something to do with unions and bit fields.  A simple test case follows.

foo.c:
extern int bar1(void);
extern void bar2(int);

void foo(char x) 
{
    union {
        int val;
        struct {
            unsigned a: 8;
        } f;
    } u;

    u.val = bar1();
    u.f.a = x;
    bar2(u.val);
}

Here is the assembly:

foo:
        stwu 1,-16(1)
        mflr 0
        stw 0,20(1)
        bl bar1
        rlwimi 3,3,24,0,7
        bl bar2
        lwz 0,20(1)
        mtlr 0
        addi 1,1,16
        blr
The input paramter to foo() is passed in r3.  r3 is not saved before calling
bar1(), and bar1() returns its value in r3, thereby overwriting the input value
of r3.  But the input value of r3 is required in the next instruction 'rlwimi
3,3,24,0,7'.

This works with gcc 3.3.1.  It also works with gcc 4.1.2 targetted for
mipsisa32-elf.  It fails with gcc 4.1.2 targetted for powerpc-elf.  My target
is an embedded system with no OS.

Here is how I build this:

$ /usr/local/trpz/trpz4.1/bin/powerpc-elf-gcc -v -save-temps -Wall -c -O -o
foo.o foo.c
Using built-in specs.
Target: powerpc-elf
Configured with: ../gcc-4.1.2/configure --prefix=/usr/local/trpz/trpz4.1
--target=powerpc-elf --enable-64-bit-bfd --disable-libssp
Thread model: single
gcc version 4.1.2

/home/gary/trpz/tools/i386-redhat-linux/trpz4.1/bin/../libexec/gcc/powerpc-elf/4.1.2/cc1
-E -quiet -v -iprefix
/home/gary/trpz/tools/i386-redhat-linux/trpz4.1/bin/../lib/gcc/powerpc-elf/4.1.2/
foo.c -Wall -O -fpch-preprocess -o foo.i
ignoring nonexistent directory
"/home/gary/trpz/tools/i386-redhat-linux/trpz4.1/bin/../lib/gcc/powerpc-elf/4.1.2/../../../../powerpc-elf/sys-include"
ignoring nonexistent directory
"/home/gary/trpz/tools/i386-redhat-linux/trpz4.1/bin/../lib/gcc/powerpc-elf/4.1.2/../../../../powerpc-elf/include"
ignoring duplicate directory
"/usr/local/trpz/trpz4.1/lib/gcc/powerpc-elf/4.1.2/include"
ignoring nonexistent directory
"/usr/local/trpz/trpz4.1/lib/gcc/powerpc-elf/4.1.2/../../../../powerpc-elf/sys-include"
ignoring nonexistent directory
"/usr/local/trpz/trpz4.1/lib/gcc/powerpc-elf/4.1.2/../../../../powerpc-elf/include"
#include "..." search starts here:
#include <...> search starts here:

/home/gary/trpz/tools/i386-redhat-linux/trpz4.1/bin/../lib/gcc/powerpc-elf/4.1.2/include
End of search list.

/home/gary/trpz/tools/i386-redhat-linux/trpz4.1/bin/../libexec/gcc/powerpc-elf/4.1.2/cc1
-fpreprocessed foo.i -quiet -dumpbase foo.c -auxbase-strip foo.o -O -Wall
-version -o foo.s
GNU C version 4.1.2 (powerpc-elf)
        compiled by GNU C version 3.2 20020903 (Red Hat Linux 8.0 3.2-7).
GGC heuristics: --param ggc-min-expand=98 --param ggc-min-heapsize=129090
Compiler executable checksum: bd93f7309b7da302bc5e08433888e36b

/home/gary/trpz/tools/i386-redhat-linux/trpz4.1/bin/../lib/gcc/powerpc-elf/4.1.2/../../../../powerpc-elf/bin/as
-mppc -many -V -Qy -o foo.o foo.s
GNU assembler version 2.17 (powerpc-elf) using BFD version 2.17

My host system is:
$ uname -por
2.6.20-1.2948.fc6 i686 GNU/Linux


-- 
           Summary: Input parameter trashed with optimization -O when using
                    a union and bit field
           Product: gcc
           Version: 4.1.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: gmorain at gmail dot com
  GCC host triplet: i386-linux-gnu
GCC target triplet: powerpc-elf


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31830


^ permalink raw reply	[flat|nested] 5+ messages in thread
[parent not found: <bug-31830-4@http.gcc.gnu.org/bugzilla/>]
end of thread, other threads:[~2012-02-02  8:25 UTC | newest]

Thread overview: 5+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2007-05-04 23:38 [Bug target/31830] New: Input parameter trashed with optimization -O when using a union and bit field gmorain at gmail dot com
2007-05-04 23:47 ` [Bug target/31830] " gmorain at gmail dot com
2007-05-04 23:49 ` [Bug rtl-optimization/31830] " pinskia at gcc dot gnu dot org
2007-05-19  1:17 ` gmorain at gmail dot com
     [not found] <bug-31830-4@http.gcc.gnu.org/bugzilla/>
2012-02-02  8:25 ` pinskia at gcc dot gnu.org

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).