| And at runtime, on some targets, we use this: | | https://llvm.org/svn/llvm-project/compiler-rt/trunk/lib/builtins/floatuntisf.c | | ... which gives a NaN in this case.
I copied that function into a test program on Ubuntu, built with gcc, and it gives me +Infinity (0x7f800000) not NaN (0x7fc00000). --paulr From: meta...@gmail.com [mailto:meta...@gmail.com] On Behalf Of Richard Smith Sent: Tuesday, December 08, 2015 11:42 AM To: Robinson, Paul Cc: Joerg Sonnenberger; cfe-commits (cfe-commits@lists.llvm.org) Subject: Re: r254574 - PR17381: Treat undefined behavior during expression evaluation as an unmodeled On Tue, Dec 8, 2015 at 11:18 AM, Richard Smith <rich...@metafoo.co.uk<mailto:rich...@metafoo.co.uk>> wrote: On Tue, Dec 8, 2015 at 10:59 AM, Robinson, Paul <paul_robin...@playstation.sony.com<mailto:paul_robin...@playstation.sony.com>> wrote: Okay, I'll bite: so what *does* UINT128_MAX actually convert to? $ echo 'unsigned __int128 max = -1; float f = max;' | ~/clang-8/build/bin/clang -x c++ - -emit-llvm -S -o - -O3 | grep @f @f = global float undef, align 4 And at runtime, on some targets, we use this: https://llvm.org/svn/llvm-project/compiler-rt/trunk/lib/builtins/floatuntisf.c ... which gives a NaN in this case. From: cfe-commits [mailto:cfe-commits-boun...@lists.llvm.org<mailto:cfe-commits-boun...@lists.llvm.org>] On Behalf Of Richard Smith via cfe-commits Sent: Tuesday, December 08, 2015 10:52 AM To: Joerg Sonnenberger; cfe-commits Subject: Re: r254574 - PR17381: Treat undefined behavior during expression evaluation as an unmodeled On Tue, Dec 8, 2015 at 2:13 AM, Joerg Sonnenberger via cfe-commits <cfe-commits@lists.llvm.org<mailto:cfe-commits@lists.llvm.org>> wrote: On Mon, Dec 07, 2015 at 01:32:14PM -0800, Richard Smith via cfe-commits wrote: > C11 6.3.1.5/1<http://6.3.1.5/1>: "If the value being converted is outside the > range of values > that can be represented, the behavior is undefined." The value of 1e100 can be represented as +inf, even if not precisely. Only if +inf is in the range of representable values, which, as already noted, is problematic. This is a bit different from non-IEEE math like VAX, that doesn't have infinities. Joerg _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org<mailto:cfe-commits@lists.llvm.org> http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
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