GCC 8.0.0 Status Report (2018-01-15), Trunk in Regression and Documentation fixes only mode

Joseph Myers joseph@codesourcery.com
Tue Feb 6 17:34:00 GMT 2018

On Tue, 6 Feb 2018, Vincent Lefevre wrote:

> Well, if I add -std=c99 or -std=c11, the failure disappears. The
> reason is that GCC generates a FMA (indeed, this new machine has
> a FMA), but this occurs across different C statements. So, maybe
> not a bug, but a bad feature, IMHO.

Use -ffp-contract=off to disable all contraction, or -ffp-contract=on to 
disable it between statements (which currently actually disables all 
contraction, as the FMA generation doesn't know what was originally a 
single source expression).  The default in the absence of such -std 
options is -ffp-contract=fast (allowing contraction including between 
different statements).

Joseph S. Myers

More information about the Gcc mailing list