forked from OSchip/llvm-project
0279b5b0b8
This might be the start of tracking all vector element constants generally if we take it to its logical conclusion, but let's stop here and make sure this is correct/beneficial so far. The affected tests require a convoluted path before they get simplified currently because we don't call SimplifyDemandedVectorElts() from binops directly and don't modify the binop operands directly in SimplifyDemandedVectorElts(). That's why the tests all have a trailing shuffle to induce a chain reaction of transforms. So something like this is happening: 1. Improve the knowledge of undefs in the binop via a SimplifyDemandedVectorElts() call that originates from a shuffle. 2. Transfer that undef knowledge back to the shuffle mask user as more undef lanes. 3. Combine the modified shuffle by calling SimplifyDemandedVectorElts() again. 4. Translate the improved shuffle mask as undemanded lanes of build vector constants causing those to become full undef constants. 5. Simplify the binop now that it has a full undef operand. As we can see from the unchanged 'and' and 'or' tests, tracking undefs alone isn't a full solution. We would need to track zero and all-ones constants to improve those opcodes. We'd probably need to track NaN for FP ops too (assuming we don't have fast-math-flags set). Differential Revision: https://reviews.llvm.org/D57066 llvm-svn: 352880 |
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| README.txt | ||
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README.txt
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