https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99494
Bug ID: 99494
Summary: isfinite gets optimized away with -Ofast
Product: gcc
Version: 10.2.0
Status: UNCONFIRMED
Keywords: wrong-code
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: arek_koz at o2 dot pl
Target Milestone: ---
Host: x86_64-pc-linux-gnu
Target: x86_64-pc-linux-gnu
Build: x86_64-pc-linux-gnu
Created attachment 50342
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=50342&action=edit
stripped _Py_HashDouble
CPython compiled with -Ofast hangs forever on python -c 'hash(float("inf"))'.
Attached is a program based on stripped _Py_HashDouble from CPython sources.
It should print 314159 when it reads an infinite number from the input.
It always prints 1 instead (the function gets reduced to "return 1").
When replacing -Ofast with -O3, the problem is gone. Likely to appear on other
build/host/target configurations.
Version: gcc (Gentoo 10.2.0-r5 p6) 10.2.0
Target architecture: x86_64 (generic)
GCC is compiled to execute on: x86_64 (znver2)
Invoked command: x86_64-pc-linux-gnu-gcc -Ofast -o bug bug.c
My best guess:
GCC -Ofast assumes that isfinite(v) is always true for any double v.
