21367b283
Denys Vlasenko
2021-04-20
Subject
tls: reduce register pressure in i386 assembly (helps Android to compile)
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networking/tls_pstm_montgomery_reduce.c+24 -0
| @@ -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( \ | |