c2a51b0cf
Denys Vlasenko
2018-02-05
Subject
bzip2: work around bad compiler optimization
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archival/libarchive/bz/compress.c+43 -32
| @@ -158,6 +158,38 @@ void makeMaps_e(EState* s) | |
| /*---------------------------------------------------*/ | |
| + | /* |
| + | * This bit of code is performance-critical. |
| + | * On 32bit x86, gcc-6.3.0 was observed to spill ryy_j to stack, |
| + | * resulting in abysmal performance (x3 slowdown). |
| + | * Forcing it into a separate function alleviates register pressure, |
| + | * and spillage no longer happens. |
| + | * Other versions of gcc do not exhibit this problem, but out-of-line code |
| + | * seems to be helping them too (code is both smaller and faster). |
| + | * Therefore NOINLINE is enabled for the entire 32bit x86 arch for now, |
| + | * without a check for gcc version. |
| + | */ |
| + | static |
| + | #if defined __i386__ |
| + | NOINLINE |
| + | #endif |
| + | int inner_loop(uint8_t *yy, uint8_t ll_i) |
| + | { |
| + | register uint8_t rtmp; |
| + | register uint8_t* ryy_j; |
| + | rtmp = yy[1]; |
| + | yy[1] = yy[0]; |
| + | ryy_j = &(yy[1]); |
| + | while (ll_i != rtmp) { |
| + | register uint8_t rtmp2; |
| + | ryy_j++; |
| + | rtmp2 = rtmp; |
| + | rtmp = *ryy_j; |
| + | *ryy_j = rtmp2; |
| + | } |
| + | yy[0] = rtmp; |
| + | return ryy_j - &(yy[0]); |
| + | } |
| static NOINLINE | |
| void generateMTFValues(EState* s) | |
| { | |
| @@ -165,7 +197,6 @@ void generateMTFValues(EState* s) | |
| int i; | |
| int zPend; | |
| int32_t wr; | |
| - | int32_t EOB; |
| /* | |
| * After sorting (eg, here), | |
| @@ -189,15 +220,12 @@ void generateMTFValues(EState* s) | |
| * compressBlock(). | |
| */ | |
| uint32_t* ptr = s->ptr; | |
| - | uint8_t* block = s->block; |
| - | uint16_t* mtfv = s->mtfv; |
| makeMaps_e(s); | |
| - | EOB = s->nInUse+1; |
| wr = 0; | |
| zPend = 0; | |
| - | for (i = 0; i <= EOB; i++) |
| + | for (i = 0; i <= s->nInUse+1; i++) |
| s->mtfFreq[i] = 0; | |
| for (i = 0; i < s->nInUse; i++) | |
| @@ -211,7 +239,7 @@ void generateMTFValues(EState* s) | |
| j = ptr[i] - 1; | |
| if (j < 0) | |
| j += s->nblock; | |
| - | ll_i = s->unseqToSeq[block[j]]; |
| + | ll_i = s->unseqToSeq[s->block[j]]; |
| AssertD(ll_i < s->nInUse, "generateMTFValues(2a)"); | |
| if (yy[0] == ll_i) { | |
| @@ -225,15 +253,15 @@ void generateMTFValues(EState* s) | |
| while (1) { | |
| #if 0 | |
| if (zPend & 1) { | |
| - | mtfv[wr] = BZ_RUNB; wr++; |
| + | s->mtfv[wr] = BZ_RUNB; wr++; |
| s->mtfFreq[BZ_RUNB]++; | |
| } else { | |
| - | mtfv[wr] = BZ_RUNA; wr++; |
| + | s->mtfv[wr] = BZ_RUNA; wr++; |
| s->mtfFreq[BZ_RUNA]++; | |
| } | |
| #else /* same as above, since BZ_RUNA is 0 and BZ_RUNB is 1 */ | |
| unsigned run = zPend & 1; | |
| - | mtfv[wr] = run; |
| + | s->mtfv[wr] = run; |
| wr++; | |
| s->mtfFreq[run]++; | |
| #endif | |
| @@ -247,36 +275,19 @@ void generateMTFValues(EState* s) | |
| goto end; | |
| zPend = 0; | |
| } | |
| - | { |
| - | register uint8_t rtmp; |
| - | register uint8_t* ryy_j; |
| - | register uint8_t rll_i; |
| - | rtmp = yy[1]; |
| - | yy[1] = yy[0]; |
| - | ryy_j = &(yy[1]); |
| - | rll_i = ll_i; |
| - | while (rll_i != rtmp) { |
| - | register uint8_t rtmp2; |
| - | ryy_j++; |
| - | rtmp2 = rtmp; |
| - | rtmp = *ryy_j; |
| - | *ryy_j = rtmp2; |
| - | } |
| - | yy[0] = rtmp; |
| - | j = ryy_j - &(yy[0]); |
| - | mtfv[wr] = j+1; |
| - | wr++; |
| - | s->mtfFreq[j+1]++; |
| - | } |
| + | j = inner_loop(yy, ll_i); |
| + | s->mtfv[wr] = j+1; |
| + | wr++; |
| + | s->mtfFreq[j+1]++; |
| } | |
| i = -1; | |
| if (zPend > 0) | |
| goto process_zPend; /* "process it and come back here" */ | |
| end: | |
| - | mtfv[wr] = EOB; |
| + | s->mtfv[wr] = s->nInUse+1; |
| wr++; | |
| - | s->mtfFreq[EOB]++; |
| + | s->mtfFreq[s->nInUse+1]++; |
| s->nMTF = wr; | |
| } | |