Ian Lance Taylor wrote:
Jeroen Demeyer <jdemeyer@xxxxxxxxxxxxx> writes:
I have a C++ program (i386 target) which has a piece of inline
assembly with the following constraints:
asm(/* Some asm code */
: "=&rm" (n0), "=&r" (n1), "=&r" (n2)
: "2" (n0), "1" (n1), "g" (n2), "cI" (s)
);
When compiled with g++ 4.1.2 (CXXFLAGS=-O2 -march=pentium4) the
operands %0 and %5 get the same memory address, even though they refer
to distinct variables (n0 and n2).
It would help to see the types of the variables. Is n2 a pointer?
Also it would help to see the actual values that wind up getting
passed in.
n0, n1, n2 are unsigned long (members of the same C++ class, the asm
statement is in a member function), s is unsigned char.
I think more details would help. For example, run gcc with the -dg
option, look at FILENAME.xxx.greg, and show us the insn corresponding
to the asm statement.
This is the full asm statement:
asm("# number_t& number_t::operator>>=(unsigned char s)\n"
" shrdl %6, %4, %3\n"
" movl %3, %0\n"
" movl %5, %2\n"
" shrdl %6, %2, %1\n"
" shrl %6, %2\n"
: "=&rm" (n0), "=&r" (n1), "=&r" (n2)
: "2" (n0), "1" (n1), "g" (n2), "cI" (s)
);
The code generated is the following:
shrdl %cl, %esi, %eax
movl %eax, -4384(%ebp)
movl -4384(%ebp), %eax
shrdl %cl, %eax, %esi
shrl %cl, %eax
As you can see, %0 and %5 both become -4384(%ebp).
See attachment for the output from -dg.
I hope this clarifies the problem.
Thank you!
(insn:HI 809 1339 1338 109 (parallel [
(set (mem/c:SI (plus:SI (reg/f:SI 6 bp)
(const_int -4384 [0xffffeee0])) [88 t$n0.805+0 S4 A8])
(asm_operands:SI ("# number_t& number_t::operator>>=(unsigned char s)
shrdl %6, %4, %3
movl %3, %0
movl %5, %2
shrdl %6, %2, %1
shrl %6, %2
") ("=&rm") 0 [
(reg:SI 0 ax)
(reg:SI 4 si)
(mem/c:SI (plus:SI (reg/f:SI 6 bp)
(const_int -4384 [0xffffeee0])) [88 t$n2+0 S4 A8])
(reg:QI 2 cx)
]
[
(asm_input:SI ("2"))
(asm_input:SI ("1"))
(asm_input:SI ("g"))
(asm_input:QI ("cI"))
] ("i386/number96.h") 148))
(set (reg:SI 4 si)
(asm_operands:SI ("# number_t& number_t::operator>>=(unsigned char s)
shrdl %6, %4, %3
movl %3, %0
movl %5, %2
shrdl %6, %2, %1
shrl %6, %2
") ("=&r") 1 [
(reg:SI 0 ax)
(reg:SI 4 si)
(mem/c:SI (plus:SI (reg/f:SI 6 bp)
(const_int -4384 [0xffffeee0])) [88 t$n2+0 S4 A8])
(reg:QI 2 cx)
]
[
(asm_input:SI ("2"))
(asm_input:SI ("1"))
(asm_input:SI ("g"))
(asm_input:QI ("cI"))
] ("i386/number96.h") 148))
(set (reg:SI 0 ax)
(asm_operands:SI ("# number_t& number_t::operator>>=(unsigned char s)
shrdl %6, %4, %3
movl %3, %0
movl %5, %2
shrdl %6, %2, %1
shrl %6, %2
") ("=&r") 2 [
(reg:SI 0 ax)
(reg:SI 4 si)
(mem/c:SI (plus:SI (reg/f:SI 6 bp)
(const_int -4384 [0xffffeee0])) [88 t$n2+0 S4 A8])
(reg:QI 2 cx)
]
[
(asm_input:SI ("2"))
(asm_input:SI ("1"))
(asm_input:SI ("g"))
(asm_input:QI ("cI"))
] ("i386/number96.h") 148))
(clobber (reg:QI 19 dirflag))
(clobber (reg:QI 18 fpsr))
(clobber (reg:QI 17 flags))
]) -1 (nil)
(nil))
