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ae76dfb747
It makes sense to split if the cost of computing `cond1` is high (proportionally to how likely `cond0` is), but it doesn't really make sense to introduce a second branch if its only a few instructions. Splitting can also get in the way of potentially folding patterns. This patch introduces some logic to try to check if the cost of computing `cond1` is relatively low, and if so don't split the branches. Modest improvement on clang bootstrap build: https://llvm-compile-time-tracker.com/compare.php?from=79ce933114e46c891a5632f7ad4a004b93a5b808&to=978278eabc0bafe2f390ca8fcdad24154f954020&stat=cycles Average stage2-O3: 0.59% Improvement (cycles) Average stage2-O0-g: 1.20% Improvement (cycles) Likewise on llvm-test-suite on SKX saw a net 0.84% improvement (cycles) There is also a modest compile time improvement with this patch: https://llvm-compile-time-tracker.com/compare.php?from=79ce933114e46c891a5632f7ad4a004b93a5b808&to=978278eabc0bafe2f390ca8fcdad24154f954020&stat=instructions%3Au Note that the stage2 instruction count increases is expected, this patch trades instructions for decreasing branch-misses (which is proportionately lower): https://llvm-compile-time-tracker.com/compare.php?from=79ce933114e46c891a5632f7ad4a004b93a5b808&to=978278eabc0bafe2f390ca8fcdad24154f954020&stat=branch-misses NB: This will also likely help for APX targets with the new `CCMP` and `CTEST` instructions. Closes #81689