We're making use of global register variables, which work fine in GCC version
4.3.2 and 4.3.3. GCC 4.4.1 and 4.4.3 however produce slightly different code,
which seems to be incorrect.
A brief example is:
//---------------test_register_call.c-------------------
register unsigned long long *g_reg_counter asm("$20");
void register_add (void)
{
*g_reg_counter++;
}
//---------------test_register_call.c-------------------
Compiled with:
mips-elf-gcc.exe -save-temps test_register_call.c
This produces the following assembler file using GCC 4.3.2
//---------------test_register_call_4.3.2.s-------------
.file 1 "test_register_call.c"
.section .mdebug.abi32
.previous
.gnu_attribute 4, 1
.text
.align 2
.globl register_add
.set nomips16
.ent register_add
register_add:
.frame $fp,8,$31 # vars= 0, regs= 1/0, args= 0, gp= 0
.mask 0x40000000,-4
.fmask 0x00000000,0
.set noreorder
.set nomacro
addiu $sp,$sp,-8
sw $fp,4($sp)
move $fp,$sp
move $2,$20
addiu $2,$2,8
move $20,$2
move $sp,$fp
lw $fp,4($sp)
addiu $sp,$sp,8
j $31
nop
.set macro
.set reorder
.end register_add
.size register_add, .-register_add
.ident "GCC: 4.3.2"
//---------------test_register_call_4.3.2.s-------------
GCC 4.4.1 produces different assembly code (lines are marked):
//---------------test_register_call_4.4.1.s-------------
.file 1 "test_register_call.c"
.section .mdebug.abi32
.previous
.gnu_attribute 4, 1
.text
.align 2
.globl register_add
.set nomips16
.ent register_add
.type register_add, @function
register_add:
.frame $fp,8,$31 # vars= 0, regs= 2/0, args= 0, gp= 0
.mask 0x40100000,-4
.fmask 0x00000000,0
.set noreorder
.set nomacro
addiu $sp,$sp,-8
sw $fp,4($sp)
sw $20,0($sp) # <== $20 is stored to stack
move $fp,$sp
move $2,$20
addiu $2,$2,8
move $20,$2
move $sp,$fp
lw $fp,4($sp)
lw $20,0($sp) # <== $20 is restored from stack
addiu $sp,$sp,8
j $31
nop
.set macro
.set reorder
.end register_add
.size register_add, .-register_add
.ident "GCC: 4.4.1"
//---------------test_register_call_4.4.1.s-------------
As can be seen in the example, MIPS register $20 is the global variable
register. The variable is modified in the function and the register should
therefore not be saved and restored. GCC 4.3.2 seems to be correct here. GCC
4.4.1, however, stores and restores the register $20 content.
--
Summary: global register variables defect
Product: gcc
Version: 4.4.3
Status: UNCONFIRMED
Severity: major
Priority: P3
Component: c
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: steffenschmidt dot ext at siemens dot com
GCC build triplet: i686-mingw32
GCC host triplet: i686-mingw32
GCC target triplet: mips-elf
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43700
