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tls: reduce register pressure in i386 assembly (helps Android to compile)

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function                                             old     new   delta
pstm_montgomery_reduce                               440     435      -5

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
This commit is contained in:
Denys Vlasenko 2021-04-20 19:01:43 +02:00
parent f277c9eebb
commit 21367b2839
1 changed files with 24 additions and 0 deletions
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24
networking/tls_pstm_montgomery_reduce.c
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@ -62,6 +62,7 @@
#define LOOP_START \
mu = c[x] * mp
#if 0
#define INNERMUL \
asm( \
"movl %5,%%eax \n\t" \
@ -74,6 +75,29 @@ asm( \
:"=g"(_c[LO]), "=r"(cy) \
:"0"(_c[LO]), "1"(cy), "g"(mu), "g"(*tmpm++) \
: "%eax", "%edx", "cc")
/*
* The above generated "error: 'asm' operand has impossible constraints" on Android.
* Do they reserve in their ABI a register for something, and there aren't enough left?
*/
#else
/* Let's avoid two explicit "movl" by telling compiler to put input value of *tmpm++
* into EAX, and to expect cy result in EDX:
*/
#define INNERMUL \
asm( \
"mull %4 \n\t" \
"addl %3,%%eax \n\t" \
"adcl $0,%%edx \n\t" \
"addl %%eax,%0 \n\t" \
"adcl $0,%%edx \n\t" \
:"=g"(_c[LO]), "=&d"(cy) \
:"0"(_c[LO]), "g"(cy), "g"(mu), "a"(*tmpm++) \
:"cc")
/* This doesn't tell compiler that we clobber EAX, but it probably won't need
* the value of *tmpm anyway, thus won't try to reuse EAX contents.
* TODO: fix it with dummy "=a"(clobbered_eax) output?
*/
#endif
#define PROPCARRY \
asm( \