Hi, I'm looking at http://llvm.org/bugs/show_bug.cgi?id=13204 which involves converting calls to sin and cos to sincos (when available) Initially I thought about transforming calls to sinf/cosf to sincosf. However, I don't think this is a legal transformation given that a declaration for a function called sinf is not necessarily the standard library function. Therefore it makes sense to transform intrinsic calls to sin and cos. One problem with this is that clang does not generate sin/cos intrinsics because they do not have the same semantics as the library functions. What is the best way to approach this transformation? (Also, experimentation shows that sincos is indeed faster than sin and cos) paul
On 22/01/13 05:30, Redmond, Paul wrote: [...]> I'm looking at http://llvm.org/bugs/show_bug.cgi?id=13204 which involves converting calls to sin and cos to sincos (when available) > > Initially I thought about transforming calls to sinf/cosf to sincosf. However, I don't think this is a legal transformation given that a declaration for a function called sinf is not necessarily the standard library function.I've actually just dealt with this --- standard library calls, including sinf, *are* promoted to intrinsics if the compiler sees them (and are then usually converted back to library calls again later). The list of recognised names is here: lib/Target/TargetLibraryInfo.cpp The list of functions which are considered candidates for promotion is in hasOptimizedCodeGen() in here: include/llvm/Target/TargetLibraryInfo.h ...and the code that actually does it is here: lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp Look for SelectionDAGBuilder::visitUnaryFloatCall() and visitCall(). It appears that such functions are only promoted if they're declared readnone, which provides some protection against overriding a standard library function, but I haven't found anything that explicitly checks for this yet. Disclaimer: I learnt this yesterday... -- ┌─── dg@cowlark.com ───── http://www.cowlark.com ───── │ "Of course, on a sufficiently small planet, 40 km/hr is, in fact, │ sufficient to punt the elastic spherical cow into low orbit." --- │ Brooks Moses on r.a.sf.c -------------- next part -------------- A non-text attachment was scrubbed... Name: signature.asc Type: application/pgp-signature Size: 262 bytes Desc: OpenPGP digital signature URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20130122/c7f54553/attachment.sig>
Hi David, On 2013-01-22, at 5:59 AM, David Given wrote:> ...and the code that actually does it is here: > > lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp > > Look for SelectionDAGBuilder::visitUnaryFloatCall() and visitCall(). > > It appears that such functions are only promoted if they're declared > readnone, which provides some protection against overriding a standard > library function, but I haven't found anything that explicitly checks > for this yet. >Thanks for the tip. I am able to see sinf to FSIN generation when I compile with -ffast-math. I don't have much experience with the selection dag but I feel like this transformation shouldn't be done at this level (it's more complicated than the transformations done by SelectionDAGCombine) Would it make sense to move library call to intrinsic generation to the IR level? paul
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