https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98207
Bug ID: 98207
Summary: ARM64 IEEE math results change with -O2
Product: gcc
Version: 7.3.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: pramsey at cleverelephant dot ca
Target Milestone: ---
Created attachment 49707
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=49707&action=edit
Test program temp files built with O0
On the ARM64 platform (in particular testing on an AWS Graviton).
Linux ip-172-31-55-124.us-west-2.compute.internal
4.14.203-156.332.amzn2.aarch64 #1 SMP Fri Oct 30 19:19:46 UTC 2020 aarch64
aarch64 aarch64 GNU/Linux
A "small" program that carries out only normal arithmetic operations on double
returns a different results if g++ is called with -O0 (or with no O at all) and
-O2.
Attached are dd-o0.ii and dd-o2.ii, the temp file outputs for compiling with
-O0 and -O2.
On x84_64, g++ compiled code returns the same answer for both O0 and O2.
On ARM64 and x84_64, clang++ returns the same answer for both O0 and O2.
This test is extracted from a small routine that provides "double double"
precision math using only arithmetic operations on IEEE compliant doubles.
https://github.com/libgeos/geos/blob/master/src/math/DD.cpp
