forked from OSchip/llvm-project
435cdecdf7
Reverse the canonicalization of fneg relative to fmul/fdiv. That makes it easier to implement the transforms (and possibly other fneg transforms) in 1 place because we can always start the pattern match from fneg (either the legacy binop or the new unop). There's a secondary practical benefit seen in PR21914 and PR42681: https://bugs.llvm.org/show_bug.cgi?id=21914 https://bugs.llvm.org/show_bug.cgi?id=42681 ...hoisting fneg rather than sinking seems to play nicer with LICM in IR (although this change may expose analysis holes in the other direction). 1. The instcombine test changes show the expected neutral IR diffs from reversing the order. 2. The reassociation tests show that we were missing an optimization opportunity to fold away fneg-of-fneg. My reading of IEEE-754 says that all of these transforms are allowed (regardless of binop/unop fneg version) because: "For all other operations [besides copy/abs/negate/copysign], this standard does not specify the sign bit of a NaN result." In all of these transforms, we always have some other binop (fadd/fsub/fmul/fdiv), so we are free to flip the sign bit of a potential intermediate NaN operand. (If that interpretation is wrong, then we must already have a bug in the existing transforms?) 3. The clang tests shouldn't exist as-is, but that's effectively a revert of rL367149 (the test broke with an extension of the pre-existing fneg canonicalization in rL367146). Differential Revision: https://reviews.llvm.org/D65399 llvm-svn: 367447 |
||
|---|---|---|
| .. | ||
| INPUTS | ||
| bindings | ||
| cmake | ||
| docs | ||
| examples | ||
| include | ||
| lib | ||
| runtime | ||
| test | ||
| tools | ||
| unittests | ||
| utils | ||
| www | ||
| .arcconfig | ||
| .clang-format | ||
| .clang-tidy | ||
| .gitignore | ||
| CMakeLists.txt | ||
| CODE_OWNERS.TXT | ||
| INSTALL.txt | ||
| LICENSE.TXT | ||
| ModuleInfo.txt | ||
| NOTES.txt | ||
| README.txt | ||
README.txt
//===----------------------------------------------------------------------===// // C Language Family Front-end //===----------------------------------------------------------------------===// Welcome to Clang. This is a compiler front-end for the C family of languages (C, C++, Objective-C, and Objective-C++) which is built as part of the LLVM compiler infrastructure project. Unlike many other compiler frontends, Clang is useful for a number of things beyond just compiling code: we intend for Clang to be host to a number of different source-level tools. One example of this is the Clang Static Analyzer. If you're interested in more (including how to build Clang) it is best to read the relevant web sites. Here are some pointers: Information on Clang: http://clang.llvm.org/ Building and using Clang: http://clang.llvm.org/get_started.html Clang Static Analyzer: http://clang-analyzer.llvm.org/ Information on the LLVM project: http://llvm.org/ If you have questions or comments about Clang, a great place to discuss them is on the Clang development mailing list: http://lists.llvm.org/mailman/listinfo/cfe-dev If you find a bug in Clang, please file it in the LLVM bug tracker: http://llvm.org/bugs/