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authorShuxin Yang <shuxin.llvm@gmail.com>2013-06-04 01:00:57 +0000
committerShuxin Yang <shuxin.llvm@gmail.com>2013-06-04 01:00:57 +0000
commit8b8fd2171c19b82b5807c3eaed2ce675b9c36258 (patch)
tree1c576a66487ec34fa2d1bad0bee72a5c5738728f /clang/lib/CodeGen/CodeGenModule.cpp
parent6df859d85954df08e201fd4506f19b20c37d49e6 (diff)
downloadbcm5719-llvm-8b8fd2171c19b82b5807c3eaed2ce675b9c36258.tar.gz
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Fix a defect in code-layout pass, improving Benchmarks/Olden/em3d/em3d by about 30%
(4.58s vs 3.2s on an oldish Mac Tower). The corresponding src is excerpted bellow. The lopp accounts for about 90% of execution time. -------------------- cat -n test-suite/MultiSource/Benchmarks/Olden/em3d/make_graph.c 90 91 for (k=0; k<j; k++) 92 if (other_node == cur_node->to_nodes[k]) break; The defective layout is sketched bellow, where the two branches need to swap. ------------------------------------------------------------------------ L: ... if (cond) goto out-of-loop goto L While this code sequence is defective, I don't understand why it incurs 1/3 of execution time. CPU-event-profiling indicates the poor laoyout dose not increase in br-misprediction; it dosen't increase stall cycle at all, and it dosen't prevent the CPU detect the loop (i.e. Loop-Stream-Detector seems to be working fine as well)... The root cause of the problem is that the layout pass calls AnalyzeBranch() with basic-block which is not updated to reflect its current layout. rdar://13966341 llvm-svn: 183174
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