On Fri, Sep 6, 2013 at 3:32 PM, Hal Finkel <[email protected]> wrote: > ----- Original Message ----- > > > > On Fri, Sep 6, 2013 at 8:27 AM, Hal Finkel < [email protected] > wrote: > > > > > > > > > > Ben, Chad, et al., > > > > The attached patch cleans up the LIBBUILTIN libm function > > definitions, and improves the way in which -ftrapping-math is > > handled in a complementary way. Specifically, this patch: > > > > 1. The libm LIBBUILTIN definitions are synchronized with the > > __builtin_* definitions for libm functions. We currently have > > __builtin_* definitions for many more functions than those for which > > we have LIBBUILTIN definitions. This unnecessarily pessimizes code > > generation around many of the remaining libm functions. > > > > 2. Many of these functions can be marked as readnone so long as we > > can neglect floating point exceptions. I've added a new specifier > > 'T', which like 'e' for errno, marks the builtin as const so long as > > trapping math is disabled. I've added a TrappingMath lang option to > > track this. > > > > 3. Disables -ftrapping-math by default. This is currently enabled by > > default (following gcc), but this is silly. No system of which I'm > > aware actually traps on floating-point exceptions by default (some > > system-specific mechanism is necessary in order to enable SIGFPE > > generation). In addition, in Clang, we currently don't support fenv > > access. As a result, we can turn this off by default (and enable > > better code generation around the functions for which we have > > LIBBUILTIN definitions). > > > > 4. Updates the CodeGen/libcall-declarations.c test case. > > > > As a side effect, the existing libm LIBBUILTIN definitions that were > > missing the 'n' (nothrow) specifier now have it. > > > > > > > > For clarity, please split the patch into four separate patches: > > reformatting, adding missing 'n' specifiers, the > > trapping-math-related changes, and adding new LIBBUILTIN definitions > > (preferably in that order). As it is, the Builtins.def changes are > > completely unreviewable. > > Unfortunately, because almost all of the LIBBUILTIN's in the patch are > new, I don't think that splitting the patch will help that :( -- FWIW, I > think that reviewing the Builtins.def changes means, in practice (either > trusting me, or) going through the documentation on each of those functions > to make sure that the flags are correct. I don't think that splitting the > patch makes that easier either. > > Nevertheless, I'll split the changes and re-post as separate patches. > Maybe I'm wrong ;) >
I didn't try to count how many were new... it looked like you were changing a bunch of existing ones, but if the balance is as you say, it might not be as useful as I'd hope. > > > > > Your changes could be substantially simplified if we don't allow > > enabling -ftrapping-math; as you've noted, we don't honor it anyway. > > What do you think? > > I considered that, but I think that we might as well not make the > situation worse for users who do enable trapping math for debugging > purposes (as I do myself on occasion). Debugging how, exactly? > With these changes, we'll mark a lot more libm functions that could trap > when exceptions are enabled as readnone (including some which never set > errno), and if we ignore -ftrapping-math completely, we'll provide no way > of indicating that those functions have side effects when we're interested > in floating point exceptions. Providing -ftrapping-math as an option is deceptive at best because clang will break code which expects us to honor -ftrapping-math, even if it doesn't even use any library calls. -Eli
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