[llvm-commits] [llvm] r103257 - in /llvm/trunk: include/llvm/LinkAllPasses.h include/llvm/Transforms/Scalar.h lib/Transforms/Scalar/Sink.cpp test/Transforms/Sink/ test/Transforms/Sink/basic.ll test/Transforms/Sink/dg.exp
Dan Gohman
gohman at apple.com
Fri May 7 08:40:13 PDT 2010
Author: djg
Date: Fri May 7 10:40:13 2010
New Revision: 103257
URL: http://llvm.org/viewvc/llvm-project?rev=103257&view=rev
Log:
Add an LLVM IR version of code sinking. This uses the same simple algorithm
as MachineSink, but it isn't constrained by MachineInstr-level details.
Added:
llvm/trunk/lib/Transforms/Scalar/Sink.cpp
llvm/trunk/test/Transforms/Sink/ (with props)
llvm/trunk/test/Transforms/Sink/basic.ll
llvm/trunk/test/Transforms/Sink/dg.exp
Modified:
llvm/trunk/include/llvm/LinkAllPasses.h
llvm/trunk/include/llvm/Transforms/Scalar.h
Modified: llvm/trunk/include/llvm/LinkAllPasses.h
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/LinkAllPasses.h?rev=103257&r1=103256&r2=103257&view=diff
==============================================================================
--- llvm/trunk/include/llvm/LinkAllPasses.h (original)
+++ llvm/trunk/include/llvm/LinkAllPasses.h Fri May 7 10:40:13 2010
@@ -138,6 +138,7 @@
(void) llvm::createGEPSplitterPass();
(void) llvm::createABCDPass();
(void) llvm::createLintPass();
+ (void) llvm::createSinkingPass();
(void)new llvm::IntervalPartition();
(void)new llvm::FindUsedTypes();
Modified: llvm/trunk/include/llvm/Transforms/Scalar.h
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/Transforms/Scalar.h?rev=103257&r1=103256&r2=103257&view=diff
==============================================================================
--- llvm/trunk/include/llvm/Transforms/Scalar.h (original)
+++ llvm/trunk/include/llvm/Transforms/Scalar.h Fri May 7 10:40:13 2010
@@ -332,6 +332,12 @@
//
FunctionPass *createABCDPass();
+//===----------------------------------------------------------------------===//
+//
+// Sink - Code Sinking
+//
+FunctionPass *createSinkingPass();
+
} // End llvm namespace
#endif
Added: llvm/trunk/lib/Transforms/Scalar/Sink.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/Sink.cpp?rev=103257&view=auto
==============================================================================
--- llvm/trunk/lib/Transforms/Scalar/Sink.cpp (added)
+++ llvm/trunk/lib/Transforms/Scalar/Sink.cpp Fri May 7 10:40:13 2010
@@ -0,0 +1,267 @@
+//===-- Sink.cpp - Code Sinking -------------------------------------------===//
+//
+// The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This pass moves instructions into successor blocks, when possible, so that
+// they aren't executed on paths where their results aren't needed.
+//
+//===----------------------------------------------------------------------===//
+
+#define DEBUG_TYPE "sink"
+#include "llvm/Transforms/Scalar.h"
+#include "llvm/IntrinsicInst.h"
+#include "llvm/Analysis/Dominators.h"
+#include "llvm/Analysis/LoopInfo.h"
+#include "llvm/Analysis/AliasAnalysis.h"
+#include "llvm/Assembly/Writer.h"
+#include "llvm/ADT/Statistic.h"
+#include "llvm/Support/CFG.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Support/raw_ostream.h"
+using namespace llvm;
+
+STATISTIC(NumSunk, "Number of instructions sunk");
+
+namespace {
+ class Sinking : public FunctionPass {
+ DominatorTree *DT;
+ LoopInfo *LI;
+ AliasAnalysis *AA;
+
+ public:
+ static char ID; // Pass identification
+ Sinking() : FunctionPass(&ID) {}
+
+ virtual bool runOnFunction(Function &F);
+
+ virtual void getAnalysisUsage(AnalysisUsage &AU) const {
+ AU.setPreservesCFG();
+ FunctionPass::getAnalysisUsage(AU);
+ AU.addRequired<AliasAnalysis>();
+ AU.addRequired<DominatorTree>();
+ AU.addRequired<LoopInfo>();
+ AU.addPreserved<DominatorTree>();
+ AU.addPreserved<LoopInfo>();
+ }
+ private:
+ bool ProcessBlock(BasicBlock &BB);
+ bool SinkInstruction(Instruction *I, SmallPtrSet<Instruction *, 8> &Stores);
+ bool AllUsesDominatedByBlock(Instruction *Inst, BasicBlock *BB) const;
+ };
+} // end anonymous namespace
+
+char Sinking::ID = 0;
+static RegisterPass<Sinking>
+X("sink", "Code sinking");
+
+FunctionPass *llvm::createSinkingPass() { return new Sinking(); }
+
+/// AllUsesDominatedByBlock - Return true if all uses of the specified value
+/// occur in blocks dominated by the specified block.
+bool Sinking::AllUsesDominatedByBlock(Instruction *Inst,
+ BasicBlock *BB) const {
+ // Ignoring debug uses is necessary so debug info doesn't affect the code.
+ // This may leave a referencing dbg_value in the original block, before
+ // the definition of the vreg. Dwarf generator handles this although the
+ // user might not get the right info at runtime.
+ for (Value::use_iterator I = Inst->use_begin(),
+ E = Inst->use_end(); I != E; ++I) {
+ // Determine the block of the use.
+ Instruction *UseInst = cast<Instruction>(*I);
+ BasicBlock *UseBlock = UseInst->getParent();
+ if (PHINode *PN = dyn_cast<PHINode>(UseInst)) {
+ // PHI nodes use the operand in the predecessor block, not the block with
+ // the PHI.
+ unsigned Num = PHINode::getIncomingValueNumForOperand(I.getOperandNo());
+ UseBlock = PN->getIncomingBlock(Num);
+ }
+ // Check that it dominates.
+ if (!DT->dominates(BB, UseBlock))
+ return false;
+ }
+ return true;
+}
+
+bool Sinking::runOnFunction(Function &F) {
+ DT = &getAnalysis<DominatorTree>();
+ LI = &getAnalysis<LoopInfo>();
+ AA = &getAnalysis<AliasAnalysis>();
+
+ bool EverMadeChange = false;
+
+ while (1) {
+ bool MadeChange = false;
+
+ // Process all basic blocks.
+ for (Function::iterator I = F.begin(), E = F.end();
+ I != E; ++I)
+ MadeChange |= ProcessBlock(*I);
+
+ // If this iteration over the code changed anything, keep iterating.
+ if (!MadeChange) break;
+ EverMadeChange = true;
+ }
+ return EverMadeChange;
+}
+
+bool Sinking::ProcessBlock(BasicBlock &BB) {
+ // Can't sink anything out of a block that has less than two successors.
+ if (BB.getTerminator()->getNumSuccessors() <= 1 || BB.empty()) return false;
+
+ // Don't bother sinking code out of unreachable blocks. In addition to being
+ // unprofitable, it can also lead to infinite looping, because in an unreachable
+ // loop there may be nowhere to stop.
+ if (!DT->isReachableFromEntry(&BB)) return false;
+
+ bool MadeChange = false;
+
+ // Walk the basic block bottom-up. Remember if we saw a store.
+ BasicBlock::iterator I = BB.end();
+ --I;
+ bool ProcessedBegin = false;
+ SmallPtrSet<Instruction *, 8> Stores;
+ do {
+ Instruction *Inst = I; // The instruction to sink.
+
+ // Predecrement I (if it's not begin) so that it isn't invalidated by
+ // sinking.
+ ProcessedBegin = I == BB.begin();
+ if (!ProcessedBegin)
+ --I;
+
+ if (isa<DbgInfoIntrinsic>(Inst))
+ continue;
+
+ if (SinkInstruction(Inst, Stores))
+ ++NumSunk, MadeChange = true;
+
+ // If we just processed the first instruction in the block, we're done.
+ } while (!ProcessedBegin);
+
+ return MadeChange;
+}
+
+static bool isSafeToMove(Instruction *Inst, AliasAnalysis *AA,
+ SmallPtrSet<Instruction *, 8> &Stores) {
+ if (LoadInst *L = dyn_cast<LoadInst>(Inst)) {
+ if (L->isVolatile()) return false;
+
+ Value *Ptr = L->getPointerOperand();
+ unsigned Size = AA->getTypeStoreSize(L->getType());
+ for (SmallPtrSet<Instruction *, 8>::iterator I = Stores.begin(),
+ E = Stores.end(); I != E; ++I)
+ if (AA->getModRefInfo(*I, Ptr, Size) & AliasAnalysis::Mod)
+ return false;
+ }
+
+ if (Inst->mayWriteToMemory()) {
+ Stores.insert(Inst);
+ return false;
+ }
+
+ return Inst->isSafeToSpeculativelyExecute();
+}
+
+/// SinkInstruction - Determine whether it is safe to sink the specified machine
+/// instruction out of its current block into a successor.
+bool Sinking::SinkInstruction(Instruction *Inst,
+ SmallPtrSet<Instruction *, 8> &Stores) {
+ // Check if it's safe to move the instruction.
+ if (!isSafeToMove(Inst, AA, Stores))
+ return false;
+
+ // FIXME: This should include support for sinking instructions within the
+ // block they are currently in to shorten the live ranges. We often get
+ // instructions sunk into the top of a large block, but it would be better to
+ // also sink them down before their first use in the block. This xform has to
+ // be careful not to *increase* register pressure though, e.g. sinking
+ // "x = y + z" down if it kills y and z would increase the live ranges of y
+ // and z and only shrink the live range of x.
+
+ // Loop over all the operands of the specified instruction. If there is
+ // anything we can't handle, bail out.
+ BasicBlock *ParentBlock = Inst->getParent();
+
+ // SuccToSinkTo - This is the successor to sink this instruction to, once we
+ // decide.
+ BasicBlock *SuccToSinkTo = 0;
+
+ // FIXME: This picks a successor to sink into based on having one
+ // successor that dominates all the uses. However, there are cases where
+ // sinking can happen but where the sink point isn't a successor. For
+ // example:
+ // x = computation
+ // if () {} else {}
+ // use x
+ // the instruction could be sunk over the whole diamond for the
+ // if/then/else (or loop, etc), allowing it to be sunk into other blocks
+ // after that.
+
+ // Instructions can only be sunk if all their uses are in blocks
+ // dominated by one of the successors.
+ // Look at all the successors and decide which one
+ // we should sink to.
+ for (succ_iterator SI = succ_begin(ParentBlock),
+ E = succ_end(ParentBlock); SI != E; ++SI) {
+ if (AllUsesDominatedByBlock(Inst, *SI)) {
+ SuccToSinkTo = *SI;
+ break;
+ }
+ }
+
+ // If we couldn't find a block to sink to, ignore this instruction.
+ if (SuccToSinkTo == 0)
+ return false;
+
+ // It is not possible to sink an instruction into its own block. This can
+ // happen with loops.
+ if (Inst->getParent() == SuccToSinkTo)
+ return false;
+
+ DEBUG(dbgs() << "Sink instr " << *Inst);
+ DEBUG(dbgs() << "to block ";
+ WriteAsOperand(dbgs(), SuccToSinkTo, false));
+
+ // If the block has multiple predecessors, this would introduce computation on
+ // a path that it doesn't already exist. We could split the critical edge,
+ // but for now we just punt.
+ // FIXME: Split critical edges if not backedges.
+ if (SuccToSinkTo->getUniquePredecessor() != ParentBlock) {
+ // We cannot sink a load across a critical edge - there may be stores in
+ // other code paths.
+ if (!Inst->isSafeToSpeculativelyExecute()) {
+ DEBUG(dbgs() << " *** PUNTING: Wont sink load along critical edge.\n");
+ return false;
+ }
+
+ // We don't want to sink across a critical edge if we don't dominate the
+ // successor. We could be introducing calculations to new code paths.
+ if (!DT->dominates(ParentBlock, SuccToSinkTo)) {
+ DEBUG(dbgs() << " *** PUNTING: Critical edge found\n");
+ return false;
+ }
+
+ // Don't sink instructions into a loop.
+ if (LI->isLoopHeader(SuccToSinkTo)) {
+ DEBUG(dbgs() << " *** PUNTING: Loop header found\n");
+ return false;
+ }
+
+ // Otherwise we are OK with sinking along a critical edge.
+ DEBUG(dbgs() << "Sinking along critical edge.\n");
+ }
+
+ // Determine where to insert into. Skip phi nodes.
+ BasicBlock::iterator InsertPos = SuccToSinkTo->begin();
+ while (InsertPos != SuccToSinkTo->end() && isa<PHINode>(InsertPos))
+ ++InsertPos;
+
+ // Move the instruction.
+ Inst->moveBefore(InsertPos);
+ return true;
+}
Propchange: llvm/trunk/test/Transforms/Sink/
------------------------------------------------------------------------------
--- svn:ignore (added)
+++ svn:ignore Fri May 7 10:40:13 2010
@@ -0,0 +1 @@
+Output
Added: llvm/trunk/test/Transforms/Sink/basic.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/Sink/basic.ll?rev=103257&view=auto
==============================================================================
--- llvm/trunk/test/Transforms/Sink/basic.ll (added)
+++ llvm/trunk/test/Transforms/Sink/basic.ll Fri May 7 10:40:13 2010
@@ -0,0 +1,22 @@
+; RUN: opt < %s -sink -S | FileCheck %s
+
+ at A = external global i32
+ at B = external global i32
+
+; Sink should sink the load past the store (which doesn't overlap) into
+; the block that uses it.
+
+; CHECK: @foo
+; CHECK: true:
+; CHECK-NEXT: %l = load i32* @A
+; CHECK-NEXT: ret i32 %l
+
+define i32 @foo(i1 %z) {
+ %l = load i32* @A
+ store i32 0, i32* @B
+ br i1 %z, label %true, label %false
+true:
+ ret i32 %l
+false:
+ ret i32 0
+}
Added: llvm/trunk/test/Transforms/Sink/dg.exp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/Sink/dg.exp?rev=103257&view=auto
==============================================================================
--- llvm/trunk/test/Transforms/Sink/dg.exp (added)
+++ llvm/trunk/test/Transforms/Sink/dg.exp Fri May 7 10:40:13 2010
@@ -0,0 +1,3 @@
+load_lib llvm.exp
+
+RunLLVMTests [lsort [glob -nocomplain $srcdir/$subdir/*.{ll,c,cpp}]]
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