jhuber6 created this revision. jhuber6 added reviewers: jdoerfert, tianshilei1992, JonChesterfield, ronlieb, ye-luo, fhahn. Herald added subscribers: StephenFan, guansong, hiraditya, inglorion, yaxunl. Herald added a project: All. jhuber6 requested review of this revision. Herald added a reviewer: sstefan1. Herald added subscribers: llvm-commits, cfe-commits, sstefan1. Herald added projects: clang, LLVM.
The `OpenMPOpt` pass is pivotal to the performance of many OpenMP offloading programs. When we perform non-LTO builds with OpenMP we used to link the OpenMP deviceRTL individually for each TU. This lead to us getting an additional attributor run on the combined runtime and user code. When we used LTO we lost a run and suffered a large performance degradation. This patch simply adds in the extra `OpenMPOpt` pass that we miss into the LTO pipeline. This patch fixes the performance regression shown in applications that used OpenMP offloading in LTO mode. Previously, this wasn't legal to do as we could emit new runtime calls into the module. That was fixed by D142646 <https://reviews.llvm.org/D142646>. Depends on D142646 <https://reviews.llvm.org/D142646> Fixes https://github.com/llvm/llvm-project/issues/60300 Repository: rG LLVM Github Monorepo https://reviews.llvm.org/D142650 Files: clang/tools/clang-linker-wrapper/ClangLinkerWrapper.cpp llvm/lib/Passes/PassBuilderPipelines.cpp Index: llvm/lib/Passes/PassBuilderPipelines.cpp =================================================================== --- llvm/lib/Passes/PassBuilderPipelines.cpp +++ llvm/lib/Passes/PassBuilderPipelines.cpp @@ -1715,6 +1715,9 @@ // Garbage collect dead functions. MPM.addPass(GlobalDCEPass()); + // Run the OpenMPOpt pass again after global optimizations. + MPM.addPass(OpenMPOptPass(ThinOrFullLTOPhase::FullLTOPostLink)); + // If we didn't decide to inline a function, check to see if we can // transform it to pass arguments by value instead of by reference. MPM.addPass(createModuleToPostOrderCGSCCPassAdaptor(ArgumentPromotionPass())); Index: clang/tools/clang-linker-wrapper/ClangLinkerWrapper.cpp =================================================================== --- clang/tools/clang-linker-wrapper/ClangLinkerWrapper.cpp +++ clang/tools/clang-linker-wrapper/ClangLinkerWrapper.cpp @@ -513,8 +513,6 @@ assert(CGOptLevelOrNone && "Invalid optimization level"); Conf.CGOptLevel = *CGOptLevelOrNone; Conf.OptLevel = OptLevel[1] - '0'; - if (Conf.OptLevel > 0) - Conf.UseDefaultPipeline = true; Conf.DefaultTriple = Triple.getTriple(); LTOError = false;
Index: llvm/lib/Passes/PassBuilderPipelines.cpp =================================================================== --- llvm/lib/Passes/PassBuilderPipelines.cpp +++ llvm/lib/Passes/PassBuilderPipelines.cpp @@ -1715,6 +1715,9 @@ // Garbage collect dead functions. MPM.addPass(GlobalDCEPass()); + // Run the OpenMPOpt pass again after global optimizations. + MPM.addPass(OpenMPOptPass(ThinOrFullLTOPhase::FullLTOPostLink)); + // If we didn't decide to inline a function, check to see if we can // transform it to pass arguments by value instead of by reference. MPM.addPass(createModuleToPostOrderCGSCCPassAdaptor(ArgumentPromotionPass())); Index: clang/tools/clang-linker-wrapper/ClangLinkerWrapper.cpp =================================================================== --- clang/tools/clang-linker-wrapper/ClangLinkerWrapper.cpp +++ clang/tools/clang-linker-wrapper/ClangLinkerWrapper.cpp @@ -513,8 +513,6 @@ assert(CGOptLevelOrNone && "Invalid optimization level"); Conf.CGOptLevel = *CGOptLevelOrNone; Conf.OptLevel = OptLevel[1] - '0'; - if (Conf.OptLevel > 0) - Conf.UseDefaultPipeline = true; Conf.DefaultTriple = Triple.getTriple(); LTOError = false;
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