From 0481d5dce311303025c6e55cd584db1870ad2492 Mon Sep 17 00:00:00 2001 From: Nathan Sidwell Date: Tue, 11 Apr 2023 17:47:31 -0400 Subject: [PATCH] bfd: optimize bfd_elf_hash The bfd_elf_hash loop is taken straight from the sysV document, but it is poorly optimized. This refactoring removes about 5 x86 insns from the 15 insn loop. 1) The if (..) is meaningless -- we're xoring with that value, and of course xor 0 is a nop. On x86 (at least) we actually compute the xor'd value and then cmov. Removing the if test removes the cmov. 2) The 'h ^ g' to clear the top 4 bits is not needed, as those 4 bits will be shifted out in the next iteration. All we need to do is sink a mask of those 4 bits out of the loop. 3) anding with 0xf0 after shifting by 24 bits can allow betterin encoding on RISC ISAs than masking with '0xf0 << 24' before shifting. RISC ISAs often require materializing larger constants. bfd/ * elf.c (bfd_elf_hash): Refactor to optimize loop. (bfd_elf_gnu_hash): Refactor to use 32-bit type. --- bfd/elf.c | 31 +++++++++++-------------------- 1 file changed, 11 insertions(+), 20 deletions(-) diff --git a/bfd/elf.c b/bfd/elf.c index 185028cbd97..0e2ae6dae1c 100644 --- a/bfd/elf.c +++ b/bfd/elf.c @@ -196,23 +196,15 @@ _bfd_elf_swap_versym_out (bfd *abfd, unsigned long bfd_elf_hash (const char *namearg) { - const unsigned char *name = (const unsigned char *) namearg; - unsigned long h = 0; - unsigned long g; - int ch; + uint32_t h = 0; - while ((ch = *name++) != '\0') + for (const unsigned char *name = (const unsigned char *) namearg; + *name; name++) { - h = (h << 4) + ch; - if ((g = (h & 0xf0000000)) != 0) - { - h ^= g >> 24; - /* The ELF ABI says `h &= ~g', but this is equivalent in - this case and on some machines one insn instead of two. */ - h ^= g; - } + h = (h << 4) + *name; + h ^= (h >> 24) & 0xf0; } - return h & 0xffffffff; + return h & 0x0fffffff; } /* DT_GNU_HASH hash function. Do not change this function; you will @@ -221,13 +213,12 @@ bfd_elf_hash (const char *namearg) unsigned long bfd_elf_gnu_hash (const char *namearg) { - const unsigned char *name = (const unsigned char *) namearg; - unsigned long h = 5381; - unsigned char ch; + uint32_t h = 5381; - while ((ch = *name++) != '\0') - h = (h << 5) + h + ch; - return h & 0xffffffff; + for (const unsigned char *name = (const unsigned char *) namearg; + *name; name++) + h = (h << 5) + h + *name; + return h; } /* Create a tdata field OBJECT_SIZE bytes in length, zeroed out and with -- 2.30.2