https://gcc.gnu.org/bugzilla/show_bug.cgi?id=120910
Bug ID: 120910
Summary: spurious underflow
Product: gcc
Version: 14.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: zimmerma+gcc at loria dot fr
Target Milestone: ---
Created attachment 61775
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=61775&action=edit
source file to reproduce the bug
with the attached code, gcc emits a spurious underflow. This was reported by
Maxence Ponsardin.
zimmerma@biscotte:/tmp/core-math$ gcc -O1 -march=x86-64-v3 -frounding-math
/tmp/e.c -lm && ./a.out
underflow: 16
y=inf
clang 19.1.7 does not emit any underflow:
zimmerma@biscotte:/tmp/core-math$ clang -O1 -march=x86-64-v3 -frounding-math
/tmp/e.c -lm && ./a.out
underflow: 0
y=inf
My guess is that the branch prediction precomputes the result of the cast from
0x1p-25f to _Float16, which would give an underflow, but in the end this branch
is not taken.
