On Mon, 22 Aug 2022 at 19:33, Segher Boessenkool <segher@xxxxxxxxxxxxxxxxxxx> wrote: > Hi! > > On Sat, Aug 20, 2022 at 11:21:50AM +0200, Andrea Bocci wrote: > > is there a way to ask GCC to produce a warning when there is a conversion > > from a floating point type (float or double) to an integer type (char, > > short, int, long, etc.), but not when there is a conversion from double > to > > float ? > > > > The reason is that we often do computations in double precision and store > > the result in single precision, so I'd rather not warn about that. > > > > -Wconversion warns about both kinds and more. > > -Wfloat-conversion warns about both kinds. > > There is no separate option. But, you can just grep the error messages? > > fc.c: In function 'f': > fc.c:1:28: warning: conversion from 'double' to 'float' may change value > [-Wfloat-conversion] > 1 | float f(double x) { return x; } > | ^ > fc.c: In function 'g': > fc.c:2:26: warning: conversion from 'double' to 'int' may change value > [-Wfloat-conversion] > 2 | int g(double x) { return x; } > | ^ > > Not ideal of course, but this should be workable? (You may want to set > LANG=C to get parsable warning messages). > > If you want a separate -W option for this, please file a PR? > See <https://gcc.gnu.org/bugs.html>. Thanks! > Hi Segher, thank you for your message ! >From a test build of our code base with -Wfloat-conversion we got over 700k warnings from 65k unique locations, the vast majority being about "warning: conversion from 'double' to 'float' may change value". So, while we can run an ad-hoc build with -Wfloat-conversion and post-process the compiler messages, it's not something we can really keep enabled all the time. Making a PR for this might be a tad complicated, but I agree it would be the best way forward... so thanks for the suggestion :-) Ciao, .Andrea -- Dr. Andrea Bocci Applied Physicist, CMS Experiment <https://cms.cern/>EP-CMD, CERN <https://home.cern/>168990 (+41 75 411 8990) CERN 40/1-B01 <https://maps.cern.ch/mapsearch/mapsearch.htm?n=['40/1-B01']> E27810 Esplanade des particules, 1, CH-1211 Geneve 23, Switzerland <https://goo.gl/maps/AMjHdhXzYk2itSu7A>