From 07288c7445bba747f65380066b1b5bdb2df5b630 Mon Sep 17 00:00:00 2001 From: John David Anglin Date: Tue, 25 Feb 2025 15:57:53 -0500 Subject: [PATCH] math: Add optimization barrier to ensure a1 + u.d is not reused [BZ #30664] A number of fma tests started to fail on hppa when gcc was changed to use Ranger rather than EVRP. Eventually I found that the value of a1 + u.d in this is block of code was being computed in FE_TOWARDZERO mode and not the original rounding mode: if (TININESS_AFTER_ROUNDING) { w.d = a1 + u.d; if (w.ieee.exponent == 109) return w.d * 0x1p-108; } This caused the exponent value to be wrong and the wrong return path to be used. Here we add an optimization barrier after the rounding mode is reset to ensure that the previous value of a1 + u.d is not reused. Signed-off-by: John David Anglin --- sysdeps/ieee754/dbl-64/s_fma.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/sysdeps/ieee754/dbl-64/s_fma.c b/sysdeps/ieee754/dbl-64/s_fma.c index 20f617b996..42351c6b34 100644 --- a/sysdeps/ieee754/dbl-64/s_fma.c +++ b/sysdeps/ieee754/dbl-64/s_fma.c @@ -244,6 +244,9 @@ __fma (double x, double y, double z) /* Reset rounding mode and test for inexact simultaneously. */ int j = libc_feupdateenv_test (&env, FE_INEXACT) != 0; + /* Ensure value of a1 + u.d is not reused. */ + a1 = math_opt_barrier (a1); + if (__glibc_likely (adjust == 0)) { if ((u.ieee.mantissa1 & 1) == 0 && u.ieee.exponent != 0x7ff)