From d2e985fd323c167e20f77b045a1d99ad166e65db Mon Sep 17 00:00:00 2001
From: rdivacky <rdivacky@FreeBSD.org>
Date: Wed, 18 Nov 2009 14:58:34 +0000
Subject: Update LLVM to r89205.
---
lib/Transforms/Utils/Local.cpp | 223 ++++++++++++++++++++++++++++++++++++++++-
1 file changed, 221 insertions(+), 2 deletions(-)
(limited to 'lib/Transforms/Utils/Local.cpp')
diff --git a/lib/Transforms/Utils/Local.cpp b/lib/Transforms/Utils/Local.cpp
index 543ddf1..aef0f5f 100644
--- a/lib/Transforms/Utils/Local.cpp
+++ b/lib/Transforms/Utils/Local.cpp
@@ -24,10 +24,14 @@
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/Analysis/ConstantFolding.h"
#include "llvm/Analysis/DebugInfo.h"
+#include "llvm/Analysis/InstructionSimplify.h"
#include "llvm/Analysis/ProfileInfo.h"
#include "llvm/Target/TargetData.h"
+#include "llvm/Support/CFG.h"
+#include "llvm/Support/Debug.h"
#include "llvm/Support/GetElementPtrTypeIterator.h"
#include "llvm/Support/MathExtras.h"
+#include "llvm/Support/raw_ostream.h"
using namespace llvm;
//===----------------------------------------------------------------------===//
@@ -236,7 +240,7 @@ bool llvm::ConstantFoldTerminator(BasicBlock *BB) {
//===----------------------------------------------------------------------===//
-// Local dead code elimination...
+// Local dead code elimination.
//
/// isInstructionTriviallyDead - Return true if the result produced by the
@@ -248,6 +252,9 @@ bool llvm::isInstructionTriviallyDead(Instruction *I) {
// We don't want debug info removed by anything this general.
if (isa<DbgInfoIntrinsic>(I)) return false;
+ // Likewise for memory use markers.
+ if (isa<MemoryUseIntrinsic>(I)) return false;
+
if (!I->mayHaveSideEffects()) return true;
// Special case intrinsics that "may have side effects" but can be deleted
@@ -323,9 +330,53 @@ llvm::RecursivelyDeleteDeadPHINode(PHINode *PN) {
}
//===----------------------------------------------------------------------===//
-// Control Flow Graph Restructuring...
+// Control Flow Graph Restructuring.
//
+
+/// RemovePredecessorAndSimplify - Like BasicBlock::removePredecessor, this
+/// method is called when we're about to delete Pred as a predecessor of BB. If
+/// BB contains any PHI nodes, this drops the entries in the PHI nodes for Pred.
+///
+/// Unlike the removePredecessor method, this attempts to simplify uses of PHI
+/// nodes that collapse into identity values. For example, if we have:
+/// x = phi(1, 0, 0, 0)
+/// y = and x, z
+///
+/// .. and delete the predecessor corresponding to the '1', this will attempt to
+/// recursively fold the and to 0.
+void llvm::RemovePredecessorAndSimplify(BasicBlock *BB, BasicBlock *Pred,
+ TargetData *TD) {
+ // This only adjusts blocks with PHI nodes.
+ if (!isa<PHINode>(BB->begin()))
+ return;
+
+ // Remove the entries for Pred from the PHI nodes in BB, but do not simplify
+ // them down. This will leave us with single entry phi nodes and other phis
+ // that can be removed.
+ BB->removePredecessor(Pred, true);
+
+ WeakVH PhiIt = &BB->front();
+ while (PHINode *PN = dyn_cast<PHINode>(PhiIt)) {
+ PhiIt = &*++BasicBlock::iterator(cast<Instruction>(PhiIt));
+
+ Value *PNV = PN->hasConstantValue();
+ if (PNV == 0) continue;
+
+ // If we're able to simplify the phi to a single value, substitute the new
+ // value into all of its uses.
+ assert(PNV != PN && "hasConstantValue broken");
+
+ ReplaceAndSimplifyAllUses(PN, PNV, TD);
+
+ // If recursive simplification ended up deleting the next PHI node we would
+ // iterate to, then our iterator is invalid, restart scanning from the top
+ // of the block.
+ if (PhiIt == 0) PhiIt = &BB->front();
+ }
+}
+
+
/// MergeBasicBlockIntoOnlyPred - DestBB is a block with one predecessor and its
/// predecessor is known to have one successor (DestBB!). Eliminate the edge
/// between them, moving the instructions in the predecessor into DestBB and
@@ -362,6 +413,174 @@ void llvm::MergeBasicBlockIntoOnlyPred(BasicBlock *DestBB, Pass *P) {
PredBB->eraseFromParent();
}
+/// CanPropagatePredecessorsForPHIs - Return true if we can fold BB, an
+/// almost-empty BB ending in an unconditional branch to Succ, into succ.
+///
+/// Assumption: Succ is the single successor for BB.
+///
+static bool CanPropagatePredecessorsForPHIs(BasicBlock *BB, BasicBlock *Succ) {
+ assert(*succ_begin(BB) == Succ && "Succ is not successor of BB!");
+
+ DEBUG(errs() << "Looking to fold " << BB->getName() << " into "
+ << Succ->getName() << "\n");
+ // Shortcut, if there is only a single predecessor it must be BB and merging
+ // is always safe
+ if (Succ->getSinglePredecessor()) return true;
+
+ // Make a list of the predecessors of BB
+ typedef SmallPtrSet<BasicBlock*, 16> BlockSet;
+ BlockSet BBPreds(pred_begin(BB), pred_end(BB));
+
+ // Use that list to make another list of common predecessors of BB and Succ
+ BlockSet CommonPreds;
+ for (pred_iterator PI = pred_begin(Succ), PE = pred_end(Succ);
+ PI != PE; ++PI)
+ if (BBPreds.count(*PI))
+ CommonPreds.insert(*PI);
+
+ // Shortcut, if there are no common predecessors, merging is always safe
+ if (CommonPreds.empty())
+ return true;
+
+ // Look at all the phi nodes in Succ, to see if they present a conflict when
+ // merging these blocks
+ for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) {
+ PHINode *PN = cast<PHINode>(I);
+
+ // If the incoming value from BB is again a PHINode in
+ // BB which has the same incoming value for *PI as PN does, we can
+ // merge the phi nodes and then the blocks can still be merged
+ PHINode *BBPN = dyn_cast<PHINode>(PN->getIncomingValueForBlock(BB));
+ if (BBPN && BBPN->getParent() == BB) {
+ for (BlockSet::iterator PI = CommonPreds.begin(), PE = CommonPreds.end();
+ PI != PE; PI++) {
+ if (BBPN->getIncomingValueForBlock(*PI)
+ != PN->getIncomingValueForBlock(*PI)) {
+ DEBUG(errs() << "Can't fold, phi node " << PN->getName() << " in "
+ << Succ->getName() << " is conflicting with "
+ << BBPN->getName() << " with regard to common predecessor "
+ << (*PI)->getName() << "\n");
+ return false;
+ }
+ }
+ } else {
+ Value* Val = PN->getIncomingValueForBlock(BB);
+ for (BlockSet::iterator PI = CommonPreds.begin(), PE = CommonPreds.end();
+ PI != PE; PI++) {
+ // See if the incoming value for the common predecessor is equal to the
+ // one for BB, in which case this phi node will not prevent the merging
+ // of the block.
+ if (Val != PN->getIncomingValueForBlock(*PI)) {
+ DEBUG(errs() << "Can't fold, phi node " << PN->getName() << " in "
+ << Succ->getName() << " is conflicting with regard to common "
+ << "predecessor " << (*PI)->getName() << "\n");
+ return false;
+ }
+ }
+ }
+ }
+
+ return true;
+}
+
+/// TryToSimplifyUncondBranchFromEmptyBlock - BB is known to contain an
+/// unconditional branch, and contains no instructions other than PHI nodes,
+/// potential debug intrinsics and the branch. If possible, eliminate BB by
+/// rewriting all the predecessors to branch to the successor block and return
+/// true. If we can't transform, return false.
+bool llvm::TryToSimplifyUncondBranchFromEmptyBlock(BasicBlock *BB) {
+ // We can't eliminate infinite loops.
+ BasicBlock *Succ = cast<BranchInst>(BB->getTerminator())->getSuccessor(0);
+ if (BB == Succ) return false;
+
+ // Check to see if merging these blocks would cause conflicts for any of the
+ // phi nodes in BB or Succ. If not, we can safely merge.
+ if (!CanPropagatePredecessorsForPHIs(BB, Succ)) return false;
+
+ // Check for cases where Succ has multiple predecessors and a PHI node in BB
+ // has uses which will not disappear when the PHI nodes are merged. It is
+ // possible to handle such cases, but difficult: it requires checking whether
+ // BB dominates Succ, which is non-trivial to calculate in the case where
+ // Succ has multiple predecessors. Also, it requires checking whether
+ // constructing the necessary self-referential PHI node doesn't intoduce any
+ // conflicts; this isn't too difficult, but the previous code for doing this
+ // was incorrect.
+ //
+ // Note that if this check finds a live use, BB dominates Succ, so BB is
+ // something like a loop pre-header (or rarely, a part of an irreducible CFG);
+ // folding the branch isn't profitable in that case anyway.
+ if (!Succ->getSinglePredecessor()) {
+ BasicBlock::iterator BBI = BB->begin();
+ while (isa<PHINode>(*BBI)) {
+ for (Value::use_iterator UI = BBI->use_begin(), E = BBI->use_end();
+ UI != E; ++UI) {
+ if (PHINode* PN = dyn_cast<PHINode>(*UI)) {
+ if (PN->getIncomingBlock(UI) != BB)
+ return false;
+ } else {
+ return false;
+ }
+ }
+ ++BBI;
+ }
+ }
+
+ DEBUG(errs() << "Killing Trivial BB: \n" << *BB);
+
+ if (isa<PHINode>(Succ->begin())) {
+ // If there is more than one pred of succ, and there are PHI nodes in
+ // the successor, then we need to add incoming edges for the PHI nodes
+ //
+ const SmallVector<BasicBlock*, 16> BBPreds(pred_begin(BB), pred_end(BB));
+
+ // Loop over all of the PHI nodes in the successor of BB.
+ for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) {
+ PHINode *PN = cast<PHINode>(I);
+ Value *OldVal = PN->removeIncomingValue(BB, false);
+ assert(OldVal && "No entry in PHI for Pred BB!");
+
+ // If this incoming value is one of the PHI nodes in BB, the new entries
+ // in the PHI node are the entries from the old PHI.
+ if (isa<PHINode>(OldVal) && cast<PHINode>(OldVal)->getParent() == BB) {
+ PHINode *OldValPN = cast<PHINode>(OldVal);
+ for (unsigned i = 0, e = OldValPN->getNumIncomingValues(); i != e; ++i)
+ // Note that, since we are merging phi nodes and BB and Succ might
+ // have common predecessors, we could end up with a phi node with
+ // identical incoming branches. This will be cleaned up later (and
+ // will trigger asserts if we try to clean it up now, without also
+ // simplifying the corresponding conditional branch).
+ PN->addIncoming(OldValPN->getIncomingValue(i),
+ OldValPN->getIncomingBlock(i));
+ } else {
+ // Add an incoming value for each of the new incoming values.
+ for (unsigned i = 0, e = BBPreds.size(); i != e; ++i)
+ PN->addIncoming(OldVal, BBPreds[i]);
+ }
+ }
+ }
+
+ while (PHINode *PN = dyn_cast<PHINode>(&BB->front())) {
+ if (Succ->getSinglePredecessor()) {
+ // BB is the only predecessor of Succ, so Succ will end up with exactly
+ // the same predecessors BB had.
+ Succ->getInstList().splice(Succ->begin(),
+ BB->getInstList(), BB->begin());
+ } else {
+ // We explicitly check for such uses in CanPropagatePredecessorsForPHIs.
+ assert(PN->use_empty() && "There shouldn't be any uses here!");
+ PN->eraseFromParent();
+ }
+ }
+
+ // Everything that jumped to BB now goes to Succ.
+ BB->replaceAllUsesWith(Succ);
+ if (!Succ->hasName()) Succ->takeName(BB);
+ BB->eraseFromParent(); // Delete the old basic block.
+ return true;
+}
+
+
+
/// OnlyUsedByDbgIntrinsics - Return true if the instruction I is only used
/// by DbgIntrinsics. If DbgInUses is specified then the vector is filled
/// with the DbgInfoIntrinsic that use the instruction I.
--
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