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gh-138114: Enable HACL BLAKE2 SIMD128 vectorization on PowerPC64 #146118

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gh-138114: Enable HACL BLAKE2 SIMD128 vectorization on PowerPC64 #146118

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db4bdde
gh-138114: Enable HACL BLAKE2 SIMD128 vectorization on PowerPC64
Scottcjn Mar 18, 2026
f8e620a
Add -flax-vector-conversions for PowerPC AltiVec/VSX HACL build
Scottcjn Mar 18, 2026
40e72eb
Add -Wno-return-type for upstream HACL control-flow warning
Scottcjn Mar 18, 2026
0849a67
Fix AltiVec bool keyword conflict with wrapper header
Scottcjn Mar 18, 2026
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3 changes: 3 additions & 0 deletions Misc/NEWS.d/next/Build/2026-03-18-00-00-00.gh-issue-138114.PwrVec.rst
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@@ -0,0 +1,3 @@
Enable HACL* BLAKE2s SIMD128 vectorization on PowerPC64 (POWER8+) using
AltiVec/VSX instructions. The HACL* library already contained a complete
PowerPC64 vec128 implementation but CPython's configure never enabled it.
32 changes: 32 additions & 0 deletions Modules/_hacl/ppc_altivec_fix.h
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/*
* PowerPC AltiVec bool keyword fix for HACL* BLAKE2 SIMD128.
*
* When GCC compiles with -maltivec, it makes "bool" a keyword meaning
* "__vector __bool int" (a 128-bit vector type). This conflicts with
* C99/C11 stdbool.h where bool means _Bool (a scalar type).
*
* The -Dbool=_Bool workaround does NOT work because altivec.h re-enables
* the keyword after the macro is defined. Instead, this header includes
* altivec.h first, then undefines the bool/true/false keywords and
* restores the C99 scalar definitions. Vector boolean types remain
* accessible via the explicit __vector __bool syntax.
*
* This header is force-included (-include) before HACL SIMD128 sources
* via LIBHACL_SIMD128_FLAGS in configure.ac.
*/
#ifndef PPC_ALTIVEC_BOOL_FIX_H
#define PPC_ALTIVEC_BOOL_FIX_H

#if defined(__ALTIVEC__) || defined(__VSX__)
#include <altivec.h>

#undef bool
#undef true
#undef false

#define bool _Bool
#define true 1
#define false 0
#endif /* __ALTIVEC__ || __VSX__ */

#endif /* PPC_ALTIVEC_BOOL_FIX_H */
54 changes: 54 additions & 0 deletions configure
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17 changes: 15 additions & 2 deletions configure.ac
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Expand Up @@ -8110,7 +8110,7 @@ fi
if test "$ac_sys_system" != "Linux-android" -a "$ac_sys_system" != "WASI" || \
{ test -n "$ANDROID_API_LEVEL" && test "$ANDROID_API_LEVEL" -ge 28; }
then
dnl This can be extended here to detect e.g. Power8, which HACL* should also support.
dnl Check for x86 SSE support (SIMD128)
AX_CHECK_COMPILE_FLAG([-msse -msse2 -msse3 -msse4.1 -msse4.2],[
[LIBHACL_SIMD128_FLAGS="-msse -msse2 -msse3 -msse4.1 -msse4.2"]

Expand All @@ -8129,7 +8129,20 @@ then
AC_MSG_RESULT([standard])
fi

], [], [-Werror])
], [
dnl x86 SSE not available; check for PowerPC AltiVec/VSX (Power8+).
dnl HACL* libintvector.h has a complete vec128 implementation for __powerpc64__.
AX_CHECK_COMPILE_FLAG([-maltivec -mvsx],[
[LIBHACL_SIMD128_FLAGS="-maltivec -mvsx -flax-vector-conversions -Wno-return-type -include \$(srcdir)/Modules/_hacl/ppc_altivec_fix.h"]

AC_DEFINE([_Py_HACL_CAN_COMPILE_VEC128], [1], [
HACL* library can compile SIMD128 implementations])

[LIBHACL_BLAKE2_SIMD128_OBJS="Modules/_hacl/Hacl_Hash_Blake2s_Simd128.o"]
AC_MSG_CHECKING([for HACL* SIMD128 implementation])
AC_MSG_RESULT([PowerPC AltiVec/VSX])
], [], [-Werror])
], [-Werror])
fi
AC_SUBST([LIBHACL_SIMD128_FLAGS])
AC_SUBST([LIBHACL_BLAKE2_SIMD128_OBJS])
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