mirror of
https://github.com/jart/cosmopolitan.git
synced 2026-11-10 10:41:27 -10:00
Justine Tunney
87d7010495
This change helps spectre more intelligently plan execution, by working around false output dependencies, impacting ops like popcnt bsr and bsf
25 lines
1.0 KiB
C
25 lines
1.0 KiB
C
#ifndef COSMOPOLITAN_LIBC_BITS_POPCNT_H_
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#define COSMOPOLITAN_LIBC_BITS_POPCNT_H_
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#include "libc/nexgen32e/x86feature.h"
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#if !(__ASSEMBLER__ + __LINKER__ + 0)
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COSMOPOLITAN_C_START_
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unsigned long popcnt(unsigned long) pureconst;
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#if defined(__GNUC__) && !defined(__STRICT_ANSI__)
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#define popcnt(X) \
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(__builtin_constant_p(X) ? __builtin_popcountll(X) : ({ \
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unsigned long PoP = (X); \
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if (X86_HAVE(POPCNT)) { \
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asm("popcnt\t%0,%0" : "+r"(PoP) : /* no inputs */ : "cc"); \
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} else { \
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PoP = (popcnt)(PoP); \
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} \
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PoP; \
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}))
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#endif /* GNUC && !ANSI */
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COSMOPOLITAN_C_END_
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#endif /* !(__ASSEMBLER__ + __LINKER__ + 0) */
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#endif /* COSMOPOLITAN_LIBC_BITS_POPCNT_H_ */
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