* Another clobber problem
@ 2006-11-21 14:24 tom
0 siblings, 0 replies; only message in thread
From: tom @ 2006-11-21 14:24 UTC (permalink / raw)
To: gcc-help
What's the right way of telling gcc that an input register is
clobbered?
I've two asm statements in the same function, both of which have "a"
(a) as an input constraint; the code corrupts RAX, and the optimiser is
not reloading a into RAX before starting the second bit of code.
If I add "rax" to the clobbers list, I get an error
modp2.cpp:55: error: can't find a register in class ___AREG___ while
reloading ___asm___
Also: how do I refer to r8 through r15 in register constraints on
x64? If I replace "r" (p) by "r9" (p) in the second asm statement, I
get an error
modp2.cpp:64: error: matching constraint references invalid operand
number
--- the function
asm("mulq %2\n mov %%rdx, %%r12 \n mov %%rax, %%r13 \n" \
"mov %3,%%rax \n mulq %%r13 \n mov %%rdx, %%r10 \n mov %%rax, %%
r11 \n" \
"mov %4,%%rax \n mulq %%r12 \n mov %%rdx, %%r8 \n mov %%rax, %%
r9 \n" \
"mov %3,%%rax \n mulq %%r12 \n add %%rax, %%r10 \n adc %%rdx, %%
r9 \n adc $0, %%r8 \n" \
"mov %4,%%rax \n mulq %%r13 \n add %%rax, %%r10 \n adc %%rdx, %%
r9 \n adc $0, %%r8 \n" \
"shrd %%cl, %%r8, %%r9\n mov %%r9, %%rdx"
: "=&d" (aus)
: "a" (a), "r" (b), "r" (il), "r" (ih), "c" (pis)
: "r8", "r9", "r10", "r11", "r12", "r13");
quotient=aus;
u64 rem;
asm("mulq %2\nmov %%rdx,%%r12 \n mov %%rax, %%r13 \n" \
"mov %3,%%rax\nmulq %4\n" \
"sub %%rax,%%r13 \n" \
"mov %%r13, %%rdx"
: "=&d" (rem)
: "a" (a), "r" (b), "c" (aus), "r" (p)
: "r12", "r13");
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