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Use __builtin_ctz and __builtin_clz in dlmalloc #18186

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Merged
kripken merged 3 commits into from
Nov 12, 2022
Merged

Use __builtin_ctz and __builtin_clz in dlmalloc #18186

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39a7a63
Use __builtin_ctz in dlmalloc
binji Nov 11, 2022
2ae156b
Use __builtin_clz too
binji Nov 11, 2022
e2d271e
rebaseline
binji Nov 11, 2022
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4 changes: 2 additions & 2 deletions system/lib/dlmalloc.c
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Original file line number Diff line number Diff line change
Expand Up @@ -2917,7 +2917,7 @@ static size_t traverse_and_check(mstate m);
#define treebin_at(M,i) (&((M)->treebins[i]))

/* assign tree index for size S to variable I. Use x86 asm if possible */
#if defined(__GNUC__) && (defined(__i386__) || defined(__x86_64__))
#if defined(__GNUC__) && (defined(__i386__) || defined(__x86_64__) || defined(__EMSCRIPTEN__))
#define compute_tree_index(S, I)\
{\
unsigned int X = S >> TREEBIN_SHIFT;\
Expand Down Expand Up @@ -3020,7 +3020,7 @@ I = (K << 1) + ((S >> (K + (TREEBIN_SHIFT-1)) & 1));\

/* index corresponding to given bit. Use x86 asm if possible */

#if defined(__GNUC__) && (defined(__i386__) || defined(__x86_64__))
#if defined(__GNUC__) && (defined(__i386__) || defined(__x86_64__) || defined(__EMSCRIPTEN__))

@sbc100 sbc100 Nov 14, 2022

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I wonder this doesn't use #if __has_builtin(__builtin_ctz) .. I guess maybe dlmalloc was written before such a macro existed?

I also wonder if we should use __wasm__ here instead of __EMSCRIPTEN__? I guess it doesn't matter much since if there is almost no chance of upstreaming these chagnes.

@binji binji Nov 15, 2022

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Yeah, __wasm__ probably is a better choice; I used __EMSCRIPTEN__ since that was used by other modifications in that file.

#define compute_bit2idx(X, I)\
{\
unsigned int J;\
Expand Down