With gcc 4.4.3 and 4.3.4 and MIPS target, code is incorrectly generated to
save/restore registers specified as "fixed" via the "-ffixed-reg" command-line
option to gcc. This also applies to register globals (which should be treated
as "fixed".)
Test code (test.c):
register int foo asm ("$23");
void test(void)
{
foo = 0;
}
Compiler invocation:
mips-unknown-linux-gnu-gcc -ffixed-s7 -O2 -c test.c
Disassembly of above code build with gcc 4.2.2 (correct):
4.2.2/test.o: file format elf32-tradbigmips
Disassembly of section .text:
00000000 <test>:
0: 03e00008 jr ra
4: 0000b821 move s7,zero
...
Disassembly with gcc 4.4.3 (incorrectly saves/restores s7, optimizes away
assignment to register global):
4.4.3/test.o: file format elf32-tradbigmips
Disassembly of section .text:
00000000 <test>:
0: 27bdfff8 addiu sp,sp,-8
4: afb70004 sw s7,4(sp)
8: 8fb70004 lw s7,4(sp)
c: 03e00008 jr ra
10: 27bd0008 addiu sp,sp,8
...
Patch that appears to fix this issue:
diff -Naur gcc-4.4.3.base/gcc/config/mips/mips.c
gcc-4.4.3/gcc/config/mips/mips.c
--- gcc-4.4.3.base/gcc/config/mips/mips.c 2010-04-09 14:10:00.235609702
-0400
+++ gcc-4.4.3/gcc/config/mips/mips.c 2010-04-09 14:12:28.520998582 -0400
@@ -8495,7 +8495,7 @@
property here. */
return (regno == GLOBAL_POINTER_REGNUM
? TARGET_CALL_SAVED_GP
- : !call_really_used_regs[regno]);
+ : !call_really_used_regs[regno] && !fixed_regs[regno]);
}
/* Return true if the function body might clobber register REGNO.
Disassembled output with above patch applied:
4.4.3fix/test.o: file format elf32-tradbigmips
Disassembly of section .text:
00000000 <test>:
0: 03e00008 jr ra
4: 0000b821 move s7,zero
...
--
Summary: -ffixed-reg and register globals broken for MIPS
Product: gcc
Version: 4.4.3
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: lance604 at gmail dot com
GCC build triplet: x86_64-build_pc-linux-gnu
GCC host triplet: x86_64-build_pc-linux-gnu
GCC target triplet: mips-unknown-linux-gnu
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43732
