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diff --git a/llvm/lib/Transforms/Scalar/SimplifyCFGPass.cpp b/llvm/lib/Transforms/Scalar/SimplifyCFGPass.cpp
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+//===- SimplifyCFGPass.cpp - CFG Simplification Pass ----------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// This file implements dead code elimination and basic block merging, along
+// with a collection of other peephole control flow optimizations. For example:
+//
+// * Removes basic blocks with no predecessors.
+// * Merges a basic block into its predecessor if there is only one and the
+// predecessor only has one successor.
+// * Eliminates PHI nodes for basic blocks with a single predecessor.
+// * Eliminates a basic block that only contains an unconditional branch.
+// * Changes invoke instructions to nounwind functions to be calls.
+// * Change things like "if (x) if (y)" into "if (x&y)".
+// * etc..
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/ADT/SmallPtrSet.h"
+#include "llvm/ADT/SmallVector.h"
+#include "llvm/ADT/Statistic.h"
+#include "llvm/Analysis/AssumptionCache.h"
+#include "llvm/Analysis/CFG.h"
+#include "llvm/Analysis/GlobalsModRef.h"
+#include "llvm/Analysis/TargetTransformInfo.h"
+#include "llvm/Transforms/Utils/Local.h"
+#include "llvm/IR/Attributes.h"
+#include "llvm/IR/CFG.h"
+#include "llvm/IR/Constants.h"
+#include "llvm/IR/DataLayout.h"
+#include "llvm/IR/Instructions.h"
+#include "llvm/IR/IntrinsicInst.h"
+#include "llvm/IR/Module.h"
+#include "llvm/Pass.h"
+#include "llvm/Support/CommandLine.h"
+#include "llvm/Transforms/Scalar.h"
+#include "llvm/Transforms/Scalar/SimplifyCFG.h"
+#include <utility>
+using namespace llvm;
+
+#define DEBUG_TYPE "simplifycfg"
+
+static cl::opt<unsigned> UserBonusInstThreshold(
+ "bonus-inst-threshold", cl::Hidden, cl::init(1),
+ cl::desc("Control the number of bonus instructions (default = 1)"));
+
+static cl::opt<bool> UserKeepLoops(
+ "keep-loops", cl::Hidden, cl::init(true),
+ cl::desc("Preserve canonical loop structure (default = true)"));
+
+static cl::opt<bool> UserSwitchToLookup(
+ "switch-to-lookup", cl::Hidden, cl::init(false),
+ cl::desc("Convert switches to lookup tables (default = false)"));
+
+static cl::opt<bool> UserForwardSwitchCond(
+ "forward-switch-cond", cl::Hidden, cl::init(false),
+ cl::desc("Forward switch condition to phi ops (default = false)"));
+
+static cl::opt<bool> UserSinkCommonInsts(
+ "sink-common-insts", cl::Hidden, cl::init(false),
+ cl::desc("Sink common instructions (default = false)"));
+
+
+STATISTIC(NumSimpl, "Number of blocks simplified");
+
+/// If we have more than one empty (other than phi node) return blocks,
+/// merge them together to promote recursive block merging.
+static bool mergeEmptyReturnBlocks(Function &F) {
+ bool Changed = false;
+
+ BasicBlock *RetBlock = nullptr;
+
+ // Scan all the blocks in the function, looking for empty return blocks.
+ for (Function::iterator BBI = F.begin(), E = F.end(); BBI != E; ) {
+ BasicBlock &BB = *BBI++;
+
+ // Only look at return blocks.
+ ReturnInst *Ret = dyn_cast<ReturnInst>(BB.getTerminator());
+ if (!Ret) continue;
+
+ // Only look at the block if it is empty or the only other thing in it is a
+ // single PHI node that is the operand to the return.
+ if (Ret != &BB.front()) {
+ // Check for something else in the block.
+ BasicBlock::iterator I(Ret);
+ --I;
+ // Skip over debug info.
+ while (isa<DbgInfoIntrinsic>(I) && I != BB.begin())
+ --I;
+ if (!isa<DbgInfoIntrinsic>(I) &&
+ (!isa<PHINode>(I) || I != BB.begin() || Ret->getNumOperands() == 0 ||
+ Ret->getOperand(0) != &*I))
+ continue;
+ }
+
+ // If this is the first returning block, remember it and keep going.
+ if (!RetBlock) {
+ RetBlock = &BB;
+ continue;
+ }
+
+ // Otherwise, we found a duplicate return block. Merge the two.
+ Changed = true;
+
+ // Case when there is no input to the return or when the returned values
+ // agree is trivial. Note that they can't agree if there are phis in the
+ // blocks.
+ if (Ret->getNumOperands() == 0 ||
+ Ret->getOperand(0) ==
+ cast<ReturnInst>(RetBlock->getTerminator())->getOperand(0)) {
+ BB.replaceAllUsesWith(RetBlock);
+ BB.eraseFromParent();
+ continue;
+ }
+
+ // If the canonical return block has no PHI node, create one now.
+ PHINode *RetBlockPHI = dyn_cast<PHINode>(RetBlock->begin());
+ if (!RetBlockPHI) {
+ Value *InVal = cast<ReturnInst>(RetBlock->getTerminator())->getOperand(0);
+ pred_iterator PB = pred_begin(RetBlock), PE = pred_end(RetBlock);
+ RetBlockPHI = PHINode::Create(Ret->getOperand(0)->getType(),
+ std::distance(PB, PE), "merge",
+ &RetBlock->front());
+
+ for (pred_iterator PI = PB; PI != PE; ++PI)
+ RetBlockPHI->addIncoming(InVal, *PI);
+ RetBlock->getTerminator()->setOperand(0, RetBlockPHI);
+ }
+
+ // Turn BB into a block that just unconditionally branches to the return
+ // block. This handles the case when the two return blocks have a common
+ // predecessor but that return different things.
+ RetBlockPHI->addIncoming(Ret->getOperand(0), &BB);
+ BB.getTerminator()->eraseFromParent();
+ BranchInst::Create(RetBlock, &BB);
+ }
+
+ return Changed;
+}
+
+/// Call SimplifyCFG on all the blocks in the function,
+/// iterating until no more changes are made.
+static bool iterativelySimplifyCFG(Function &F, const TargetTransformInfo &TTI,
+ const SimplifyCFGOptions &Options) {
+ bool Changed = false;
+ bool LocalChange = true;
+
+ SmallVector<std::pair<const BasicBlock *, const BasicBlock *>, 32> Edges;
+ FindFunctionBackedges(F, Edges);
+ SmallPtrSet<BasicBlock *, 16> LoopHeaders;
+ for (unsigned i = 0, e = Edges.size(); i != e; ++i)
+ LoopHeaders.insert(const_cast<BasicBlock *>(Edges[i].second));
+
+ while (LocalChange) {
+ LocalChange = false;
+
+ // Loop over all of the basic blocks and remove them if they are unneeded.
+ for (Function::iterator BBIt = F.begin(); BBIt != F.end(); ) {
+ if (simplifyCFG(&*BBIt++, TTI, Options, &LoopHeaders)) {
+ LocalChange = true;
+ ++NumSimpl;
+ }
+ }
+ Changed |= LocalChange;
+ }
+ return Changed;
+}
+
+static bool simplifyFunctionCFG(Function &F, const TargetTransformInfo &TTI,
+ const SimplifyCFGOptions &Options) {
+ bool EverChanged = removeUnreachableBlocks(F);
+ EverChanged |= mergeEmptyReturnBlocks(F);
+ EverChanged |= iterativelySimplifyCFG(F, TTI, Options);
+
+ // If neither pass changed anything, we're done.
+ if (!EverChanged) return false;
+
+ // iterativelySimplifyCFG can (rarely) make some loops dead. If this happens,
+ // removeUnreachableBlocks is needed to nuke them, which means we should
+ // iterate between the two optimizations. We structure the code like this to
+ // avoid rerunning iterativelySimplifyCFG if the second pass of
+ // removeUnreachableBlocks doesn't do anything.
+ if (!removeUnreachableBlocks(F))
+ return true;
+
+ do {
+ EverChanged = iterativelySimplifyCFG(F, TTI, Options);
+ EverChanged |= removeUnreachableBlocks(F);
+ } while (EverChanged);
+
+ return true;
+}
+
+// Command-line settings override compile-time settings.
+SimplifyCFGPass::SimplifyCFGPass(const SimplifyCFGOptions &Opts) {
+ Options.BonusInstThreshold = UserBonusInstThreshold.getNumOccurrences()
+ ? UserBonusInstThreshold
+ : Opts.BonusInstThreshold;
+ Options.ForwardSwitchCondToPhi = UserForwardSwitchCond.getNumOccurrences()
+ ? UserForwardSwitchCond
+ : Opts.ForwardSwitchCondToPhi;
+ Options.ConvertSwitchToLookupTable = UserSwitchToLookup.getNumOccurrences()
+ ? UserSwitchToLookup
+ : Opts.ConvertSwitchToLookupTable;
+ Options.NeedCanonicalLoop = UserKeepLoops.getNumOccurrences()
+ ? UserKeepLoops
+ : Opts.NeedCanonicalLoop;
+ Options.SinkCommonInsts = UserSinkCommonInsts.getNumOccurrences()
+ ? UserSinkCommonInsts
+ : Opts.SinkCommonInsts;
+}
+
+PreservedAnalyses SimplifyCFGPass::run(Function &F,
+ FunctionAnalysisManager &AM) {
+ auto &TTI = AM.getResult<TargetIRAnalysis>(F);
+ Options.AC = &AM.getResult<AssumptionAnalysis>(F);
+ if (!simplifyFunctionCFG(F, TTI, Options))
+ return PreservedAnalyses::all();
+ PreservedAnalyses PA;
+ PA.preserve<GlobalsAA>();
+ return PA;
+}
+
+namespace {
+struct CFGSimplifyPass : public FunctionPass {
+ static char ID;
+ SimplifyCFGOptions Options;
+ std::function<bool(const Function &)> PredicateFtor;
+
+ CFGSimplifyPass(unsigned Threshold = 1, bool ForwardSwitchCond = false,
+ bool ConvertSwitch = false, bool KeepLoops = true,
+ bool SinkCommon = false,
+ std::function<bool(const Function &)> Ftor = nullptr)
+ : FunctionPass(ID), PredicateFtor(std::move(Ftor)) {
+
+ initializeCFGSimplifyPassPass(*PassRegistry::getPassRegistry());
+
+ // Check for command-line overrides of options for debug/customization.
+ Options.BonusInstThreshold = UserBonusInstThreshold.getNumOccurrences()
+ ? UserBonusInstThreshold
+ : Threshold;
+
+ Options.ForwardSwitchCondToPhi = UserForwardSwitchCond.getNumOccurrences()
+ ? UserForwardSwitchCond
+ : ForwardSwitchCond;
+
+ Options.ConvertSwitchToLookupTable = UserSwitchToLookup.getNumOccurrences()
+ ? UserSwitchToLookup
+ : ConvertSwitch;
+
+ Options.NeedCanonicalLoop =
+ UserKeepLoops.getNumOccurrences() ? UserKeepLoops : KeepLoops;
+
+ Options.SinkCommonInsts = UserSinkCommonInsts.getNumOccurrences()
+ ? UserSinkCommonInsts
+ : SinkCommon;
+ }
+
+ bool runOnFunction(Function &F) override {
+ if (skipFunction(F) || (PredicateFtor && !PredicateFtor(F)))
+ return false;
+
+ Options.AC = &getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F);
+ auto &TTI = getAnalysis<TargetTransformInfoWrapperPass>().getTTI(F);
+ return simplifyFunctionCFG(F, TTI, Options);
+ }
+ void getAnalysisUsage(AnalysisUsage &AU) const override {
+ AU.addRequired<AssumptionCacheTracker>();
+ AU.addRequired<TargetTransformInfoWrapperPass>();
+ AU.addPreserved<GlobalsAAWrapperPass>();
+ }
+};
+}
+
+char CFGSimplifyPass::ID = 0;
+INITIALIZE_PASS_BEGIN(CFGSimplifyPass, "simplifycfg", "Simplify the CFG", false,
+ false)
+INITIALIZE_PASS_DEPENDENCY(TargetTransformInfoWrapperPass)
+INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
+INITIALIZE_PASS_END(CFGSimplifyPass, "simplifycfg", "Simplify the CFG", false,
+ false)
+
+// Public interface to the CFGSimplification pass
+FunctionPass *
+llvm::createCFGSimplificationPass(unsigned Threshold, bool ForwardSwitchCond,
+ bool ConvertSwitch, bool KeepLoops,
+ bool SinkCommon,
+ std::function<bool(const Function &)> Ftor) {
+ return new CFGSimplifyPass(Threshold, ForwardSwitchCond, ConvertSwitch,
+ KeepLoops, SinkCommon, std::move(Ftor));
+}
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