https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110182
Bug ID: 110182
Summary: GCC generates incorrect results for simple Eigen Casts
/ Subtractions at -O2 or above for a 3 dimensional
vector
Product: gcc
Version: 13.1.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: lakin at vividtheory dot com
Target Milestone: ---
Created attachment 55286
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=55286&action=edit
The minimal reproducing example
I am attaching a simple example program that shows how gcc is getting an
incorrect result for a simple program which is attempting to represent a 1D
matrix of doubles as two floating point matrices, one for the closest value as
a float and one for the remainder.
gcc 11 gets correct results at -O1 and -O2, but not -O3. gcc 12/13 get
incorrect results at -O2 and -O3, but not at -O1.
I've attached the source file below, and am more than happy to provide more
information / intermediate outputs. However, one can reproduce this even at
godbolt: https://godbolt.org/z/j7P5of7xo
More info here:
https://gist.github.com/lakinwecker/9ef9dbde94c018a33f4c33822c6d93ad
