On Sun, Aug 9, 2026 at 8:03 AM Kael Andrew Alonzo Franco <[email protected]> wrote: > > hwint.cc reflect_hwi uses a naive for loop approach to > emulate __builtin_bitreverse64 (). > This is slow compared to using __builtin_bitreverse64 () plus bitshift. > This is useful for bootstrapping GCC since r17-523. > Also add assert on BITWIDTH <= 64. > > For reflect_hwi and ira-color.cc, add STAGE0_CXX_HAS_BUILTIN > in system.h to test for specific builtins. > > Bootstrapped and regtested on x86_64-pc-linux-gnu. > > PR middle-end/126625 > > gcc/ChangeLog: > > * hwint.cc (reflect_hwi): Use STAGE0_CXX_HAS_BUILTIN > for __builtin_bitreverse64. > * ira-color.cc (HAS_SMUL_OVERFLOW): Remove > and use STAGE0_CXX_HAS_BUILTIN instead. > * system.h (STAGE0_CXX_HAS_BUILTIN): New macro.
I can't think of a better name for this macro so ok, > > Signed-off-by: Kael Andrew Franco <[email protected]> > --- > gcc/hwint.cc | 13 ++++++++++++- > gcc/ira-color.cc | 7 +------ > gcc/system.h | 8 ++++++++ > 3 files changed, 21 insertions(+), 7 deletions(-) > > diff --git a/gcc/hwint.cc b/gcc/hwint.cc > index f3b3e7b8408..da7bc05f085 100644 > --- a/gcc/hwint.cc > +++ b/gcc/hwint.cc > @@ -189,12 +189,21 @@ least_common_multiple (HOST_WIDE_INT a, HOST_WIDE_INT b) > return mul_hwi (abs_hwi (a) / gcd (a, b), abs_hwi (b)); > } > > -/* Reflect (reverse) the bits of a given VALUE within a specified BITWIDTH. > */ > +/* Reflect (reverse) the bits of a given VALUE within a specified BITWIDTH > <= 64. */ > > unsigned HOST_WIDE_INT > reflect_hwi (unsigned HOST_WIDE_INT value, unsigned bitwidth) > { > + if (bitwidth == 0) > + return 0; > + > + gcc_checking_assert (bitwidth <= 64); > + > +#if STAGE0_CXX_HAS_BUILTIN (bitreverse64) > + return __builtin_bitreverse64 (value) >> (64 - bitwidth); > +#else > unsigned HOST_WIDE_INT reflected_value = 0; > + > /* Loop through each bit in the specified BITWIDTH. */ > for (size_t i = 0; i < bitwidth; i++) > { > @@ -204,5 +213,7 @@ reflect_hwi (unsigned HOST_WIDE_INT value, unsigned > bitwidth) > reflected_value |= (value & 1); > value >>= 1; > } > + > return reflected_value; > +#endif > } > diff --git a/gcc/ira-color.cc b/gcc/ira-color.cc > index 2b389b5aab1..866d5b6bec3 100644 > --- a/gcc/ira-color.cc > +++ b/gcc/ira-color.cc > @@ -3154,14 +3154,9 @@ setup_allocno_priorities (ira_allocno_t > *consideration_allocnos, int n) > ira_assert (mult >= 0); > mult *= ira_reg_class_max_nregs[ALLOCNO_CLASS (a)][ALLOCNO_MODE (a)]; > diff = ALLOCNO_MEMORY_COST (a) - ALLOCNO_CLASS_COST (a); > -#ifdef __has_builtin > -#if __has_builtin(__builtin_smul_overflow) > -#define HAS_SMUL_OVERFLOW > -#endif > -#endif > /* Multiplication can overflow for very large functions. > Check the overflow and constrain the result if necessary: */ > -#ifdef HAS_SMUL_OVERFLOW > +#if STAGE0_CXX_HAS_BUILTIN (smul_overflow) > if (__builtin_smul_overflow (mult, diff, &priority) > || priority < -INT_MAX) > priority = diff >= 0 ? INT_MAX : -INT_MAX; > diff --git a/gcc/system.h b/gcc/system.h > index f0fa062d469..08fefd6f054 100644 > --- a/gcc/system.h > +++ b/gcc/system.h > @@ -22,6 +22,14 @@ along with GCC; see the file COPYING3. If not see > #ifndef GCC_SYSTEM_H > #define GCC_SYSTEM_H > > +/* True if __builtin_* () is supported. > + This is done for optimizing GCC itself. */ > +#ifdef __has_builtin > +# define STAGE0_CXX_HAS_BUILTIN(NAME) __has_builtin (__builtin_ ## NAME) > +#else > +# define STAGE0_CXX_HAS_BUILTIN(NAME) 0 > +#endif > + > /* Define this so that inttypes.h defines the PRI?64 macros even > when compiling with a C++ compiler. Define it here so in the > event inttypes.h gets pulled in by another header it is already > -- > 2.55.0 >
