From 57b96253346fe679c82b7f88e2398ec21553b52c Mon Sep 17 00:00:00 2001 From: Szabolcs Nagy Date: Mon, 15 Mar 2021 11:44:32 +0000 Subject: malloc: Ensure mtag code path in checked_request2size is cold This is a workaround (hack) for a gcc optimization issue (PR 99551). Without this the generated code may evaluate the expression in the cold path which causes performance regression for small allocations in the memory tagging disabled (common) case. --- malloc/malloc.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-) diff --git a/malloc/malloc.c b/malloc/malloc.c index cb1837d0d7..ef1f5b1621 100644 --- a/malloc/malloc.c +++ b/malloc/malloc.c @@ -1357,8 +1357,13 @@ checked_request2size (size_t req, size_t *sz) __nonnull (1) must be a macro that produces a compile time constant if passed a constant literal. */ if (__glibc_unlikely (mtag_enabled)) - req = (req + (__MTAG_GRANULE_SIZE - 1)) & - ~(size_t)(__MTAG_GRANULE_SIZE - 1); + { + /* Ensure this is not evaluated if !mtag_enabled, see gcc PR 99551. */ + asm (""); + + req = (req + (__MTAG_GRANULE_SIZE - 1)) & + ~(size_t)(__MTAG_GRANULE_SIZE - 1); + } *sz = request2size (req); return true; -- cgit 1.4.1