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Merging r245820: ------------------------------------------------------------------------ r245820 | mehdi.amini | 2015-08-23 18:15:49 -0400 (Sun, 23 Aug 2015) | 64 lines Require Dominator Tree For SROA, improve compile-time TL-DR: SROA is followed by EarlyCSE which requires the DominatorTree. There is no reason not to require it up-front for SROA. Some history is necessary to understand why we ended-up here. r123437 switched the second (Legacy)SROA in the optimizer pipeline to use SSAUpdater in order to avoid recomputing the costly DominanceFrontier. The purpose was to speed-up the compile-time. Later r123609 removed the need for the DominanceFrontier in (Legacy)SROA. Right after, some cleanup was made in r123724 to remove any reference to the DominanceFrontier. SROA existed in two flavors: SROA_SSAUp and SROA_DT (the latter replacing SROA_DF). The second argument of `createScalarReplAggregatesPass` was renamed from `UseDomFrontier` to `UseDomTree`. I believe this is were a mistake was made. The pipeline was not updated and the call site was still: PM->add(createScalarReplAggregatesPass(-1, false)); At that time, SROA was immediately followed in the pipeline by EarlyCSE which required alread the DominatorTree. Not requiring the DominatorTree in SROA didn't save anything, but unfortunately it was lost at this point. When the new SROA Pass was introduced in r163965, I believe the goal was to have an exact replacement of the existing SROA, this bug slipped through. You can see currently: $ echo "" | clang -x c++ -O3 -c - -mllvm -debug-pass=Structure ... ... FunctionPass Manager SROA Dominator Tree Construction Early CSE After this patch: $ echo "" | clang -x c++ -O3 -c - -mllvm -debug-pass=Structure ... ... FunctionPass Manager Dominator Tree Construction SROA Early CSE This improves the compile time from 88s to 23s for PR17855. https://llvm.org/bugs/show_bug.cgi?id=17855 And from 113s to 12s for PR16756 https://llvm.org/bugs/show_bug.cgi?id=16756 Reviewers: chandlerc Differential Revision: http://reviews.llvm.org/D12267 From: Mehdi Amini <mehdi.amini@apple.com> ------------------------------------------------------------------------ git-svn-id: https://llvm.org/svn/llvm-project/llvm/branches/release_37@252510 91177308-0d34-0410-b5e6-96231b3b80d8 Tom Stellard 3 years ago
1 changed file(s) with 1 addition(s) and 1 deletion(s). Raw diff Collapse all Expand all
227227 // Start of function pass.
228228 // Break up aggregate allocas, using SSAUpdater.
229229 if (UseNewSROA)
230 MPM.add(createSROAPass(/*RequiresDomTree*/ false));
230 MPM.add(createSROAPass());
231231 else
232232 MPM.add(createScalarReplAggregatesPass(-1, false));
233233 MPM.add(createEarlyCSEPass()); // Catch trivial redundancies