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author | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-06-12 05:43:14 +0000 |
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committer | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-06-12 05:43:14 +0000 |
commit | 8dd16259287f58f9273002717ec4d27e97127719 (patch) | |
tree | 3863e62a53829a84037444beab3abd4ed9dfc7d0 /js/src/jit/BranchHinting.cpp | |
parent | Releasing progress-linux version 126.0.1-1~progress7.99u1. (diff) | |
download | firefox-8dd16259287f58f9273002717ec4d27e97127719.tar.xz firefox-8dd16259287f58f9273002717ec4d27e97127719.zip |
Merging upstream version 127.0.
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to 'js/src/jit/BranchHinting.cpp')
-rw-r--r-- | js/src/jit/BranchHinting.cpp | 61 |
1 files changed, 61 insertions, 0 deletions
diff --git a/js/src/jit/BranchHinting.cpp b/js/src/jit/BranchHinting.cpp new file mode 100644 index 0000000000..01c311267f --- /dev/null +++ b/js/src/jit/BranchHinting.cpp @@ -0,0 +1,61 @@ +/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- + * vim: set ts=8 sts=2 et sw=2 tw=80: + * This Source Code Form is subject to the terms of the Mozilla Public + * License, v. 2.0. If a copy of the MPL was not distributed with this + * file, You can obtain one at http://mozilla.org/MPL/2.0/. */ + +#include "jit/BranchHinting.h" + +#include "jit/IonAnalysis.h" +#include "jit/JitSpewer.h" +#include "jit/MIRGenerator.h" +#include "jit/MIRGraph.h" + +using namespace js; +using namespace js::jit; + +// Implementation of the branch hinting proposal +// Some control instructions (if and br_if) can have a hint of the form +// Likely or unlikely. That means a specific branch will be likely/unlikely +// to be executed at runtime. + +// In a first pass, we tag the basic blocks if we have a hint. +// In a Mir to Mir transformation, we read the hints and do something with it: +// - Unlikely blocks are pushed to the end of the function. +// Because of Ion's structure, we don't do that for blocks inside a loop. +// - TODO: do something for likely blocks. +// - TODO: register allocator can be tuned depending on the hints. +bool jit::BranchHinting(MIRGenerator* mir, MIRGraph& graph) { + JitSpew(JitSpew_BranchHint, "Beginning BranchHinting pass"); + + // Move towards the end all blocks marked as unlikely + mozilla::Vector<MBasicBlock*, 0> toBeMoved; + + for (MBasicBlock* block : graph) { + // If this block has a return instruction, it's safe to push it + // to the end of the graph. + // If the block doesn't contain a return, a backedge outside a loop will be + // created, which would break ReversePostOrder assertions. + // Avoid moving a block if it's in the middle of a loop as well. + if (block->branchHintingUnlikely() && block->loopDepth() == 0 && + block->hasLastIns() && block->lastIns()->is<js::jit::MWasmReturn>()) { + if (!toBeMoved.append(block)) { + return false; + } + } + } + + for (MBasicBlock* block : toBeMoved) { +#ifdef JS_JITSPEW + JitSpew(JitSpew_BranchHint, "Moving block%u to the end", block->id()); +#endif + graph.moveBlockToEnd(block); + } + + if (!toBeMoved.empty()) { + // Renumber blocks after moving them around. + RenumberBlocks(graph); + } + + return true; +} |