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Document dummy register clobbers in raid_sse_end and raid_neon_end

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Andrea Mazzoleni 2026-08-06 22:46:54 +02:00
parent acdf29ac09
commit f3c3265116
1 changed files with 21 additions and 0 deletions
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21
raid/internal.h
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@ -368,6 +368,15 @@ static __always_inline void raid_sse_end(void)
* clobber them freely.
*
* Registers ymm and zmm don't have this requirement.
*
* Note: Placing dummy clobber lists at the end of the function rather
* than on individual inner asm statements is not a strictly conforming
* inline assembly pattern. However, because the inner loops use only
* scalar integer variables for loop counters and pointers (which GCC and
* Clang allocate to general-purpose integer registers), and because the
* function calls are dispatched via pointers (preventing inlining), this
* workaround successfully forces GCC and Clang to save and restore
* callee-saved registers in the function prologue/epilogue for the Windows ABI.
*/
#ifdef __SSE2__
asm volatile ("" : : : "%xmm0", "%xmm1", "%xmm2", "%xmm3");
@ -404,6 +413,18 @@ static __always_inline void raid_neon_begin(void)
static __always_inline void raid_neon_end(void)
{
/*
* Clobbers registers used in NEON asm operations.
*
* Note: Placing dummy clobber lists at the end of the function rather
* than on individual inner asm statements is not a strictly conforming
* inline assembly pattern. However, because the inner loops use only
* scalar integer variables for loop counters and pointers (which GCC and
* Clang allocate to general-purpose integer registers), and because the
* function calls are dispatched via pointers (preventing inlining), this
* workaround successfully forces GCC and Clang to save and restore AAPCS64
* callee-saved registers (v8-v15) in the function prologue/epilogue.
*/
asm volatile ("" : : : "v0", "v1", "v2", "v3", "v4", "v5", "v6", "v7");
asm volatile ("" : : : "v8", "v9", "v10", "v11", "v12", "v13", "v14", "v15");
asm volatile ("" : : : "v16", "v17", "v18", "v19", "v20", "v21", "v22", "v23");