forked from OSchip/llvm-project
4805ce0b17
Notably, no regression tests change when we remove these calls, and these are expensive calls. The motivation comes from the general acknowledgement that the compiler is getting slower: http://lists.llvm.org/pipermail/llvm-dev/2017-January/109188.html http://lists.llvm.org/pipermail/llvm-dev/2016-December/108279.html And specifically the test case attached to PR32037: https://bugs.llvm.org//show_bug.cgi?id=32037 Profiling the middle-end (opt) part of the compile: $ ./opt -O2 row_common.bc -o /dev/null ...visitAdd and visitSub are near the top of the instcombine list, and the calls to SimplifyDemandedInstructionBits() are high within each of those. Those calls account for 1%+ of the opt time in either debug or release profiles. And that's the rough win I see from this patch when testing opt built release from r295864 on an iMac with Haswell 4GHz (model 4790K). It seems unlikely that we'd be able to eliminate add/sub or change their operands given that add/sub normally affect all bits, and the PR32037 example shows no IR difference after this change using -O2. Also worth noting - the code comment in visitAdd: // This handles stuff like (X & 254)+1 -> (X&254)|1 ...isn't true. That transform is handled later with a call to haveNoCommonBitsSet(). Differential Revision: https://reviews.llvm.org/D30270 llvm-svn: 295898 |
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| clang | ||
| clang-tools-extra | ||
| compiler-rt | ||
| debuginfo-tests | ||
| libclc | ||
| libcxx | ||
| libcxxabi | ||
| libunwind | ||
| lld | ||
| lldb | ||
| llgo | ||
| llvm | ||
| openmp | ||
| parallel-libs | ||
| polly | ||