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From: "vincent-gcc at vinc17 dot net" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c/114746] With FLT_EVAL_METHOD = 2, -fexcess-precision=fast
 reduces the precision of floating-point constants
Date: Wed, 17 Apr 2024 23:18:38 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D114746

--- Comment #1 from Vincent Lef=C3=A8vre <vincent-gcc at vinc17 dot net> ---
There is the same issue with constant floating-point expressions.

Consider the following program given at
  https://github.com/llvm/llvm-project/issues/89128

#include <float.h>
#include <stdio.h>

static double const_init =3D 1.0 + (DBL_EPSILON/2) + (DBL_EPSILON/2);
int main() {
    double nonconst_init =3D 1.0;
    nonconst_init =3D nonconst_init + (DBL_EPSILON/2) + (DBL_EPSILON/2);
    printf("FLT_EVAL_METHOD =3D %d\n", FLT_EVAL_METHOD);
    printf("const: %g\n", const_init - 1.0);
    printf("nonconst: %g\n", (double)nonconst_init - 1.0);
}

With -m32 -mno-sse, one gets

FLT_EVAL_METHOD =3D 2
const: 0
nonconst: 2.22045e-16

instead of

FLT_EVAL_METHOD =3D 2
const: 2.22045e-16
nonconst: 2.22045e-16=