[llvm] r207783 - Add an optimization that does CSE in a group of similar GEPs.
Eli Bendersky
eliben at google.com
Thu May 1 11:38:36 PDT 2014
Author: eliben
Date: Thu May 1 13:38:36 2014
New Revision: 207783
URL: http://llvm.org/viewvc/llvm-project?rev=207783&view=rev
Log:
Add an optimization that does CSE in a group of similar GEPs.
This optimization merges the common part of a group of GEPs, so we can compute
each pointer address by adding a simple offset to the common part.
The optimization is currently only enabled for the NVPTX backend, where it has
a large payoff on some benchmarks.
Review: http://reviews.llvm.org/D3462
Patch by Jingyue Wu.
Added:
llvm/trunk/lib/Transforms/Scalar/SeparateConstOffsetFromGEP.cpp
llvm/trunk/test/Transforms/SeparateConstOffsetFromGEP/
llvm/trunk/test/Transforms/SeparateConstOffsetFromGEP/NVPTX/
llvm/trunk/test/Transforms/SeparateConstOffsetFromGEP/NVPTX/lit.local.cfg
llvm/trunk/test/Transforms/SeparateConstOffsetFromGEP/NVPTX/split-gep-and-gvn.ll
llvm/trunk/test/Transforms/SeparateConstOffsetFromGEP/NVPTX/split-gep.ll
Modified:
llvm/trunk/include/llvm/InitializePasses.h
llvm/trunk/include/llvm/LinkAllPasses.h
llvm/trunk/include/llvm/Transforms/Scalar.h
llvm/trunk/lib/Target/NVPTX/NVPTXTargetMachine.cpp
llvm/trunk/lib/Transforms/Scalar/Scalar.cpp
Modified: llvm/trunk/include/llvm/InitializePasses.h
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/InitializePasses.h?rev=207783&r1=207782&r2=207783&view=diff
==============================================================================
--- llvm/trunk/include/llvm/InitializePasses.h (original)
+++ llvm/trunk/include/llvm/InitializePasses.h Thu May 1 13:38:36 2014
@@ -238,6 +238,7 @@ void initializeSimpleInlinerPass(PassReg
void initializeRegisterCoalescerPass(PassRegistry&);
void initializeSingleLoopExtractorPass(PassRegistry&);
void initializeSinkingPass(PassRegistry&);
+void initializeSeparateConstOffsetFromGEPPass(PassRegistry &);
void initializeSlotIndexesPass(PassRegistry&);
void initializeSpillPlacementPass(PassRegistry&);
void initializeStackProtectorPass(PassRegistry&);
Modified: llvm/trunk/include/llvm/LinkAllPasses.h
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/LinkAllPasses.h?rev=207783&r1=207782&r2=207783&view=diff
==============================================================================
--- llvm/trunk/include/llvm/LinkAllPasses.h (original)
+++ llvm/trunk/include/llvm/LinkAllPasses.h Thu May 1 13:38:36 2014
@@ -156,6 +156,7 @@ namespace {
(void) llvm::createBBVectorizePass();
(void) llvm::createPartiallyInlineLibCallsPass();
(void) llvm::createScalarizerPass();
+ (void) llvm::createSeparateConstOffsetFromGEPPass();
(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=207783&r1=207782&r2=207783&view=diff
==============================================================================
--- llvm/trunk/include/llvm/Transforms/Scalar.h (original)
+++ llvm/trunk/include/llvm/Transforms/Scalar.h Thu May 1 13:38:36 2014
@@ -377,6 +377,12 @@ FunctionPass *createScalarizerPass();
// AddDiscriminators - Add DWARF path discriminators to the IR.
FunctionPass *createAddDiscriminatorsPass();
+//===----------------------------------------------------------------------===//
+//
+// SeparateConstOffsetFromGEP - Split GEPs for better CSE
+//
+FunctionPass *createSeparateConstOffsetFromGEPPass();
+
} // End llvm namespace
#endif
Modified: llvm/trunk/lib/Target/NVPTX/NVPTXTargetMachine.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/NVPTX/NVPTXTargetMachine.cpp?rev=207783&r1=207782&r2=207783&view=diff
==============================================================================
--- llvm/trunk/lib/Target/NVPTX/NVPTXTargetMachine.cpp (original)
+++ llvm/trunk/lib/Target/NVPTX/NVPTXTargetMachine.cpp Thu May 1 13:38:36 2014
@@ -147,10 +147,23 @@ void NVPTXPassConfig::addIRPasses() {
addPass(createNVPTXAssignValidGlobalNamesPass());
addPass(createGenericToNVVMPass());
addPass(createNVPTXFavorNonGenericAddrSpacesPass());
- // The FavorNonGenericAddrSpaces pass may remove instructions and leave some
- // values unused. Therefore, we run a DCE pass right afterwards. We could
- // remove unused values in an ad-hoc manner, but it requires manual work and
- // might be error-prone.
+ addPass(createSeparateConstOffsetFromGEPPass());
+ // The SeparateConstOffsetFromGEP pass creates variadic bases that can be used
+ // by multiple GEPs. Run GVN or EarlyCSE to really reuse them. GVN generates
+ // significantly better code than EarlyCSE for some of our benchmarks.
+ if (getOptLevel() == CodeGenOpt::Aggressive)
+ addPass(createGVNPass());
+ else
+ addPass(createEarlyCSEPass());
+ // Both FavorNonGenericAddrSpaces and SeparateConstOffsetFromGEP may leave
+ // some dead code. We could remove dead code in an ad-hoc manner, but that
+ // requires manual work and might be error-prone.
+ //
+ // The FavorNonGenericAddrSpaces pass shortcuts unnecessary addrspacecasts,
+ // and leave them unused.
+ //
+ // SeparateConstOffsetFromGEP rebuilds a new index from the old index, and the
+ // old index and some of its intermediate results may become unused.
addPass(createDeadCodeEliminationPass());
}
Modified: llvm/trunk/lib/Transforms/Scalar/Scalar.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/Scalar.cpp?rev=207783&r1=207782&r2=207783&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Scalar/Scalar.cpp (original)
+++ llvm/trunk/lib/Transforms/Scalar/Scalar.cpp Thu May 1 13:38:36 2014
@@ -64,6 +64,7 @@ void llvm::initializeScalarOpts(PassRegi
initializeStructurizeCFGPass(Registry);
initializeSinkingPass(Registry);
initializeTailCallElimPass(Registry);
+ initializeSeparateConstOffsetFromGEPPass(Registry);
}
void LLVMInitializeScalarOpts(LLVMPassRegistryRef R) {
Added: llvm/trunk/lib/Transforms/Scalar/SeparateConstOffsetFromGEP.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/SeparateConstOffsetFromGEP.cpp?rev=207783&view=auto
==============================================================================
--- llvm/trunk/lib/Transforms/Scalar/SeparateConstOffsetFromGEP.cpp (added)
+++ llvm/trunk/lib/Transforms/Scalar/SeparateConstOffsetFromGEP.cpp Thu May 1 13:38:36 2014
@@ -0,0 +1,583 @@
+//===-- SeparateConstOffsetFromGEP.cpp - ------------------------*- C++ -*-===//
+//
+// The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// Loop unrolling may create many similar GEPs for array accesses.
+// e.g., a 2-level loop
+//
+// float a[32][32]; // global variable
+//
+// for (int i = 0; i < 2; ++i) {
+// for (int j = 0; j < 2; ++j) {
+// ...
+// ... = a[x + i][y + j];
+// ...
+// }
+// }
+//
+// will probably be unrolled to:
+//
+// gep %a, 0, %x, %y; load
+// gep %a, 0, %x, %y + 1; load
+// gep %a, 0, %x + 1, %y; load
+// gep %a, 0, %x + 1, %y + 1; load
+//
+// LLVM's GVN does not use partial redundancy elimination yet, and is thus
+// unable to reuse (gep %a, 0, %x, %y). As a result, this misoptimization incurs
+// significant slowdown in targets with limited addressing modes. For instance,
+// because the PTX target does not support the reg+reg addressing mode, the
+// NVPTX backend emits PTX code that literally computes the pointer address of
+// each GEP, wasting tons of registers. It emits the following PTX for the
+// first load and similar PTX for other loads.
+//
+// mov.u32 %r1, %x;
+// mov.u32 %r2, %y;
+// mul.wide.u32 %rl2, %r1, 128;
+// mov.u64 %rl3, a;
+// add.s64 %rl4, %rl3, %rl2;
+// mul.wide.u32 %rl5, %r2, 4;
+// add.s64 %rl6, %rl4, %rl5;
+// ld.global.f32 %f1, [%rl6];
+//
+// To reduce the register pressure, the optimization implemented in this file
+// merges the common part of a group of GEPs, so we can compute each pointer
+// address by adding a simple offset to the common part, saving many registers.
+//
+// It works by splitting each GEP into a variadic base and a constant offset.
+// The variadic base can be computed once and reused by multiple GEPs, and the
+// constant offsets can be nicely folded into the reg+immediate addressing mode
+// (supported by most targets) without using any extra register.
+//
+// For instance, we transform the four GEPs and four loads in the above example
+// into:
+//
+// base = gep a, 0, x, y
+// load base
+// laod base + 1 * sizeof(float)
+// load base + 32 * sizeof(float)
+// load base + 33 * sizeof(float)
+//
+// Given the transformed IR, a backend that supports the reg+immediate
+// addressing mode can easily fold the pointer arithmetics into the loads. For
+// example, the NVPTX backend can easily fold the pointer arithmetics into the
+// ld.global.f32 instructions, and the resultant PTX uses much fewer registers.
+//
+// mov.u32 %r1, %tid.x;
+// mov.u32 %r2, %tid.y;
+// mul.wide.u32 %rl2, %r1, 128;
+// mov.u64 %rl3, a;
+// add.s64 %rl4, %rl3, %rl2;
+// mul.wide.u32 %rl5, %r2, 4;
+// add.s64 %rl6, %rl4, %rl5;
+// ld.global.f32 %f1, [%rl6]; // so far the same as unoptimized PTX
+// ld.global.f32 %f2, [%rl6+4]; // much better
+// ld.global.f32 %f3, [%rl6+128]; // much better
+// ld.global.f32 %f4, [%rl6+132]; // much better
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Analysis/TargetTransformInfo.h"
+#include "llvm/Analysis/ValueTracking.h"
+#include "llvm/IR/Constants.h"
+#include "llvm/IR/DataLayout.h"
+#include "llvm/IR/Instructions.h"
+#include "llvm/IR/LLVMContext.h"
+#include "llvm/IR/Module.h"
+#include "llvm/IR/Operator.h"
+#include "llvm/Support/CommandLine.h"
+#include "llvm/Support/raw_ostream.h"
+#include "llvm/Transforms/Scalar.h"
+
+using namespace llvm;
+
+static cl::opt<bool> DisableSeparateConstOffsetFromGEP(
+ "disable-separate-const-offset-from-gep", cl::init(false),
+ cl::desc("Do not separate the constant offset from a GEP instruction"),
+ cl::Hidden);
+
+namespace {
+
+/// \brief A helper class for separating a constant offset from a GEP index.
+///
+/// In real programs, a GEP index may be more complicated than a simple addition
+/// of something and a constant integer which can be trivially splitted. For
+/// example, to split ((a << 3) | 5) + b, we need to search deeper for the
+/// constant offset, so that we can seperate the index to (a << 3) + b and 5.
+///
+/// Therefore, this class looks into the expression that computes a given GEP
+/// index, and tries to find a constant integer that can be hoisted to the
+/// outermost level of the expression as an addition. Not every constant in an
+/// expression can jump out. e.g., we cannot transform (b * (a + 5)) to (b * a +
+/// 5); nor can we transform (3 * (a + 5)) to (3 * a + 5), however in this case,
+/// -instcombine probably already optimized (3 * (a + 5)) to (3 * a + 15).
+class ConstantOffsetExtractor {
+ public:
+ /// Extracts a constant offset from the given GEP index. It outputs the
+ /// numeric value of the extracted constant offset (0 if failed), and a
+ /// new index representing the remainder (equal to the original index minus
+ /// the constant offset).
+ /// \p Idx The given GEP index
+ /// \p NewIdx The new index to replace
+ /// \p DL The datalayout of the module
+ /// \p IP Calculating the new index requires new instructions. IP indicates
+ /// where to insert them (typically right before the GEP).
+ static int64_t Extract(Value *Idx, Value *&NewIdx, const DataLayout *DL,
+ Instruction *IP);
+ /// Looks for a constant offset without extracting it. The meaning of the
+ /// arguments and the return value are the same as Extract.
+ static int64_t Find(Value *Idx, const DataLayout *DL);
+
+ private:
+ ConstantOffsetExtractor(const DataLayout *Layout, Instruction *InsertionPt)
+ : DL(Layout), IP(InsertionPt) {}
+ /// Searches the expression that computes V for a constant offset. If the
+ /// searching is successful, update UserChain as a path from V to the constant
+ /// offset.
+ int64_t find(Value *V);
+ /// A helper function to look into both operands of a binary operator U.
+ /// \p IsSub Whether U is a sub operator. If so, we need to negate the
+ /// constant offset at some point.
+ int64_t findInEitherOperand(User *U, bool IsSub);
+ /// After finding the constant offset and how it is reached from the GEP
+ /// index, we build a new index which is a clone of the old one except the
+ /// constant offset is removed. For example, given (a + (b + 5)) and knowning
+ /// the constant offset is 5, this function returns (a + b).
+ ///
+ /// We cannot simply change the constant to zero because the expression that
+ /// computes the index or its intermediate result may be used by others.
+ Value *rebuildWithoutConstantOffset();
+ // A helper function for rebuildWithoutConstantOffset that rebuilds the direct
+ // user (U) of the constant offset (C).
+ Value *rebuildLeafWithoutConstantOffset(User *U, Value *C);
+ /// Returns a clone of U except the first occurrence of From with To.
+ Value *cloneAndReplace(User *U, Value *From, Value *To);
+
+ /// Returns true if LHS and RHS have no bits in common, i.e., LHS | RHS == 0.
+ bool NoCommonBits(Value *LHS, Value *RHS) const;
+ /// Computes which bits are known to be one or zero.
+ /// \p KnownOne Mask of all bits that are known to be one.
+ /// \p KnownZero Mask of all bits that are known to be zero.
+ void ComputeKnownBits(Value *V, APInt &KnownOne, APInt &KnownZero) const;
+ /// Finds the first use of Used in U. Returns -1 if not found.
+ static unsigned FindFirstUse(User *U, Value *Used);
+
+ /// The path from the constant offset to the old GEP index. e.g., if the GEP
+ /// index is "a * b + (c + 5)". After running function find, UserChain[0] will
+ /// be the constant 5, UserChain[1] will be the subexpression "c + 5", and
+ /// UserChain[2] will be the entire expression "a * b + (c + 5)".
+ ///
+ /// This path helps rebuildWithoutConstantOffset rebuild the new GEP index.
+ SmallVector<User *, 8> UserChain;
+ /// The data layout of the module. Used in ComputeKnownBits.
+ const DataLayout *DL;
+ Instruction *IP; /// Insertion position of cloned instructions.
+};
+
+/// \brief A pass that tries to split every GEP in the function into a variadic
+/// base and a constant offset. It is a FuntionPass because searching for the
+/// constant offset may inspect other basic blocks.
+class SeparateConstOffsetFromGEP : public FunctionPass {
+ public:
+ static char ID;
+ SeparateConstOffsetFromGEP() : FunctionPass(ID) {
+ initializeSeparateConstOffsetFromGEPPass(*PassRegistry::getPassRegistry());
+ }
+
+ void getAnalysisUsage(AnalysisUsage &AU) const override {
+ AU.addRequired<DataLayoutPass>();
+ AU.addRequired<TargetTransformInfo>();
+ }
+ bool runOnFunction(Function &F) override;
+
+ private:
+ /// Tries to split the given GEP into a variadic base and a constant offset,
+ /// and returns true if the splitting succeeds.
+ bool splitGEP(GetElementPtrInst *GEP);
+ /// Finds the constant offset within each index, and accumulates them. This
+ /// function only inspects the GEP without changing it. The output
+ /// NeedsExtraction indicates whether we can extract a non-zero constant
+ /// offset from any index.
+ int64_t accumulateByteOffset(GetElementPtrInst *GEP, const DataLayout *DL,
+ bool &NeedsExtraction);
+};
+} // anonymous namespace
+
+char SeparateConstOffsetFromGEP::ID = 0;
+INITIALIZE_PASS_BEGIN(
+ SeparateConstOffsetFromGEP, "separate-const-offset-from-gep",
+ "Split GEPs to a variadic base and a constant offset for better CSE", false,
+ false)
+INITIALIZE_AG_DEPENDENCY(TargetTransformInfo)
+INITIALIZE_PASS_DEPENDENCY(DataLayoutPass)
+INITIALIZE_PASS_END(
+ SeparateConstOffsetFromGEP, "separate-const-offset-from-gep",
+ "Split GEPs to a variadic base and a constant offset for better CSE", false,
+ false)
+
+FunctionPass *llvm::createSeparateConstOffsetFromGEPPass() {
+ return new SeparateConstOffsetFromGEP();
+}
+
+int64_t ConstantOffsetExtractor::findInEitherOperand(User *U, bool IsSub) {
+ assert(U->getNumOperands() == 2);
+ int64_t ConstantOffset = find(U->getOperand(0));
+ // If we found a constant offset in the left operand, stop and return that.
+ // This shortcut might cause us to miss opportunities of combining the
+ // constant offsets in both operands, e.g., (a + 4) + (b + 5) => (a + b) + 9.
+ // However, such cases are probably already handled by -instcombine,
+ // given this pass runs after the standard optimizations.
+ if (ConstantOffset != 0) return ConstantOffset;
+ ConstantOffset = find(U->getOperand(1));
+ // If U is a sub operator, negate the constant offset found in the right
+ // operand.
+ return IsSub ? -ConstantOffset : ConstantOffset;
+}
+
+int64_t ConstantOffsetExtractor::find(Value *V) {
+ // TODO(jingyue): We can even trace into integer/pointer casts, such as
+ // inttoptr, ptrtoint, bitcast, and addrspacecast. We choose to handle only
+ // integers because it gives good enough results for our benchmarks.
+ assert(V->getType()->isIntegerTy());
+
+ User *U = dyn_cast<User>(V);
+ // We cannot do much with Values that are not a User, such as BasicBlock and
+ // MDNode.
+ if (U == nullptr) return 0;
+
+ int64_t ConstantOffset = 0;
+ if (ConstantInt *CI = dyn_cast<ConstantInt>(U)) {
+ // Hooray, we found it!
+ ConstantOffset = CI->getSExtValue();
+ } else if (Operator *O = dyn_cast<Operator>(U)) {
+ // The GEP index may be more complicated than a simple addition of a
+ // varaible and a constant. Therefore, we trace into subexpressions for more
+ // hoisting opportunities.
+ switch (O->getOpcode()) {
+ case Instruction::Add: {
+ ConstantOffset = findInEitherOperand(U, false);
+ break;
+ }
+ case Instruction::Sub: {
+ ConstantOffset = findInEitherOperand(U, true);
+ break;
+ }
+ case Instruction::Or: {
+ // If LHS and RHS don't have common bits, (LHS | RHS) is equivalent to
+ // (LHS + RHS).
+ if (NoCommonBits(U->getOperand(0), U->getOperand(1)))
+ ConstantOffset = findInEitherOperand(U, false);
+ break;
+ }
+ case Instruction::SExt: {
+ // For safety, we trace into sext only when its operand is marked
+ // "nsw" because xxx.nsw guarantees no signed wrap. e.g., we can safely
+ // transform "sext (add nsw a, 5)" into "add nsw (sext a), 5".
+ if (BinaryOperator *BO = dyn_cast<BinaryOperator>(U->getOperand(0))) {
+ if (BO->hasNoSignedWrap())
+ ConstantOffset = find(U->getOperand(0));
+ }
+ break;
+ }
+ case Instruction::ZExt: {
+ // Similarly, we trace into zext only when its operand is marked with
+ // "nuw" because zext (add nuw a, b) == add nuw (zext a), (zext b).
+ if (BinaryOperator *BO = dyn_cast<BinaryOperator>(U->getOperand(0))) {
+ if (BO->hasNoUnsignedWrap())
+ ConstantOffset = find(U->getOperand(0));
+ }
+ break;
+ }
+ }
+ }
+ // If we found a non-zero constant offset, adds it to the path for future
+ // transformation (rebuildWithoutConstantOffset). Zero is a valid constant
+ // offset, but doesn't help this optimization.
+ if (ConstantOffset != 0)
+ UserChain.push_back(U);
+ return ConstantOffset;
+}
+
+unsigned ConstantOffsetExtractor::FindFirstUse(User *U, Value *Used) {
+ for (unsigned I = 0, E = U->getNumOperands(); I < E; ++I) {
+ if (U->getOperand(I) == Used)
+ return I;
+ }
+ return -1;
+}
+
+Value *ConstantOffsetExtractor::cloneAndReplace(User *U, Value *From,
+ Value *To) {
+ // Finds in U the first use of From. It is safe to ignore future occurrences
+ // of From, because findInEitherOperand similarly stops searching the right
+ // operand when the first operand has a non-zero constant offset.
+ unsigned OpNo = FindFirstUse(U, From);
+ assert(OpNo != (unsigned)-1 && "UserChain wasn't built correctly");
+
+ // ConstantOffsetExtractor::find only follows Operators (i.e., Instructions
+ // and ConstantExprs). Therefore, U is either an Instruction or a
+ // ConstantExpr.
+ if (Instruction *I = dyn_cast<Instruction>(U)) {
+ Instruction *Clone = I->clone();
+ Clone->setOperand(OpNo, To);
+ Clone->insertBefore(IP);
+ return Clone;
+ }
+ // cast<Constant>(To) is safe because a ConstantExpr only uses Constants.
+ return cast<ConstantExpr>(U)
+ ->getWithOperandReplaced(OpNo, cast<Constant>(To));
+}
+
+Value *ConstantOffsetExtractor::rebuildLeafWithoutConstantOffset(User *U,
+ Value *C) {
+ assert(U->getNumOperands() <= 2 &&
+ "We didn't trace into any operator with more than 2 operands");
+ // If U has only one operand which is the constant offset, removing the
+ // constant offset leaves U as a null value.
+ if (U->getNumOperands() == 1)
+ return Constant::getNullValue(U->getType());
+
+ // U->getNumOperands() == 2
+ unsigned OpNo = FindFirstUse(U, C); // U->getOperand(OpNo) == C
+ assert(OpNo < 2 && "UserChain wasn't built correctly");
+ Value *TheOther = U->getOperand(1 - OpNo); // The other operand of U
+ // If U = C - X, removing C makes U = -X; otherwise U will simply be X.
+ if (!isa<SubOperator>(U) || OpNo == 1)
+ return TheOther;
+ if (isa<ConstantExpr>(U))
+ return ConstantExpr::getNeg(cast<Constant>(TheOther));
+ return BinaryOperator::CreateNeg(TheOther, "", IP);
+}
+
+Value *ConstantOffsetExtractor::rebuildWithoutConstantOffset() {
+ assert(UserChain.size() > 0 && "you at least found a constant, right?");
+ // Start with the constant and go up through UserChain, each time building a
+ // clone of the subexpression but with the constant removed.
+ // e.g., to build a clone of (a + (b + (c + 5)) but with the 5 removed, we
+ // first c, then (b + c), and finally (a + (b + c)).
+ //
+ // Fast path: if the GEP index is a constant, simply returns 0.
+ if (UserChain.size() == 1)
+ return ConstantInt::get(UserChain[0]->getType(), 0);
+
+ Value *Remainder =
+ rebuildLeafWithoutConstantOffset(UserChain[1], UserChain[0]);
+ for (size_t I = 2; I < UserChain.size(); ++I)
+ Remainder = cloneAndReplace(UserChain[I], UserChain[I - 1], Remainder);
+ return Remainder;
+}
+
+int64_t ConstantOffsetExtractor::Extract(Value *Idx, Value *&NewIdx,
+ const DataLayout *DL,
+ Instruction *IP) {
+ ConstantOffsetExtractor Extractor(DL, IP);
+ // Find a non-zero constant offset first.
+ int64_t ConstantOffset = Extractor.find(Idx);
+ if (ConstantOffset == 0)
+ return 0;
+ // Then rebuild a new index with the constant removed.
+ NewIdx = Extractor.rebuildWithoutConstantOffset();
+ return ConstantOffset;
+}
+
+int64_t ConstantOffsetExtractor::Find(Value *Idx, const DataLayout *DL) {
+ return ConstantOffsetExtractor(DL, nullptr).find(Idx);
+}
+
+void ConstantOffsetExtractor::ComputeKnownBits(Value *V, APInt &KnownOne,
+ APInt &KnownZero) const {
+ IntegerType *IT = cast<IntegerType>(V->getType());
+ KnownOne = APInt(IT->getBitWidth(), 0);
+ KnownZero = APInt(IT->getBitWidth(), 0);
+ llvm::ComputeMaskedBits(V, KnownZero, KnownOne, DL, 0);
+}
+
+bool ConstantOffsetExtractor::NoCommonBits(Value *LHS, Value *RHS) const {
+ assert(LHS->getType() == RHS->getType() &&
+ "LHS and RHS should have the same type");
+ APInt LHSKnownOne, LHSKnownZero, RHSKnownOne, RHSKnownZero;
+ ComputeKnownBits(LHS, LHSKnownOne, LHSKnownZero);
+ ComputeKnownBits(RHS, RHSKnownOne, RHSKnownZero);
+ return (LHSKnownZero | RHSKnownZero).isAllOnesValue();
+}
+
+int64_t SeparateConstOffsetFromGEP::accumulateByteOffset(
+ GetElementPtrInst *GEP, const DataLayout *DL, bool &NeedsExtraction) {
+ NeedsExtraction = false;
+ int64_t AccumulativeByteOffset = 0;
+ gep_type_iterator GTI = gep_type_begin(*GEP);
+ for (unsigned I = 1, E = GEP->getNumOperands(); I != E; ++I, ++GTI) {
+ if (isa<SequentialType>(*GTI)) {
+ // Tries to extract a constant offset from this GEP index.
+ int64_t ConstantOffset =
+ ConstantOffsetExtractor::Find(GEP->getOperand(I), DL);
+ if (ConstantOffset != 0) {
+ NeedsExtraction = true;
+ // A GEP may have multiple indices. We accumulate the extracted
+ // constant offset to a byte offset, and later offset the remainder of
+ // the original GEP with this byte offset.
+ AccumulativeByteOffset +=
+ ConstantOffset * DL->getTypeAllocSize(GTI.getIndexedType());
+ }
+ }
+ }
+ return AccumulativeByteOffset;
+}
+
+bool SeparateConstOffsetFromGEP::splitGEP(GetElementPtrInst *GEP) {
+ // Skip vector GEPs.
+ if (GEP->getType()->isVectorTy())
+ return false;
+
+ // The backend can already nicely handle the case where all indices are
+ // constant.
+ if (GEP->hasAllConstantIndices())
+ return false;
+
+ bool Changed = false;
+
+ // Shortcuts integer casts. Eliminating these explicit casts can make
+ // subsequent optimizations more obvious: ConstantOffsetExtractor needn't
+ // trace into these casts.
+ if (GEP->isInBounds()) {
+ // Doing this to inbounds GEPs is safe because their indices are guaranteed
+ // to be non-negative and in bounds.
+ gep_type_iterator GTI = gep_type_begin(*GEP);
+ for (unsigned I = 1, E = GEP->getNumOperands(); I != E; ++I, ++GTI) {
+ if (isa<SequentialType>(*GTI)) {
+ if (Operator *O = dyn_cast<Operator>(GEP->getOperand(I))) {
+ if (O->getOpcode() == Instruction::SExt ||
+ O->getOpcode() == Instruction::ZExt) {
+ GEP->setOperand(I, O->getOperand(0));
+ Changed = true;
+ }
+ }
+ }
+ }
+ }
+
+ const DataLayout *DL = &getAnalysis<DataLayoutPass>().getDataLayout();
+ bool NeedsExtraction;
+ int64_t AccumulativeByteOffset =
+ accumulateByteOffset(GEP, DL, NeedsExtraction);
+
+ if (!NeedsExtraction)
+ return Changed;
+ // Before really splitting the GEP, check whether the backend supports the
+ // addressing mode we are about to produce. If no, this splitting probably
+ // won't be beneficial.
+ TargetTransformInfo &TTI = getAnalysis<TargetTransformInfo>();
+ if (!TTI.isLegalAddressingMode(GEP->getType()->getElementType(),
+ /*BaseGV=*/nullptr, AccumulativeByteOffset,
+ /*HasBaseReg=*/true, /*Scale=*/0)) {
+ return Changed;
+ }
+
+ // Remove the constant offset in each GEP index. The resultant GEP computes
+ // the variadic base.
+ gep_type_iterator GTI = gep_type_begin(*GEP);
+ for (unsigned I = 1, E = GEP->getNumOperands(); I != E; ++I, ++GTI) {
+ if (isa<SequentialType>(*GTI)) {
+ Value *NewIdx = nullptr;
+ // Tries to extract a constant offset from this GEP index.
+ int64_t ConstantOffset =
+ ConstantOffsetExtractor::Extract(GEP->getOperand(I), NewIdx, DL, GEP);
+ if (ConstantOffset != 0) {
+ assert(NewIdx && "ConstantOffset != 0 implies NewIdx is set");
+ GEP->setOperand(I, NewIdx);
+ // Clear the inbounds attribute because the new index may be off-bound.
+ // e.g.,
+ //
+ // b = add i64 a, 5
+ // addr = gep inbounds float* p, i64 b
+ //
+ // is transformed to:
+ //
+ // addr2 = gep float* p, i64 a
+ // addr = gep float* addr2, i64 5
+ //
+ // If a is -4, although the old index b is in bounds, the new index a is
+ // off-bound. http://llvm.org/docs/LangRef.html#id181 says "if the
+ // inbounds keyword is not present, the offsets are added to the base
+ // address with silently-wrapping two's complement arithmetic".
+ // Therefore, the final code will be a semantically equivalent.
+ //
+ // TODO(jingyue): do some range analysis to keep as many inbounds as
+ // possible. GEPs with inbounds are more friendly to alias analysis.
+ GEP->setIsInBounds(false);
+ Changed = true;
+ }
+ }
+ }
+
+ // Offsets the base with the accumulative byte offset.
+ //
+ // %gep ; the base
+ // ... %gep ...
+ //
+ // => add the offset
+ //
+ // %gep2 ; clone of %gep
+ // %0 = ptrtoint %gep2
+ // %1 = add %0, <offset>
+ // %new.gep = inttoptr %1
+ // %gep ; will be removed
+ // ... %gep ...
+ //
+ // => replace all uses of %gep with %new.gep and remove %gep
+ //
+ // %gep2 ; clone of %gep
+ // %0 = ptrtoint %gep2
+ // %1 = add %0, <offset>
+ // %new.gep = inttoptr %1
+ // ... %new.gep ...
+ //
+ // TODO(jingyue): Emit a GEP instead of an "uglygep"
+ // (http://llvm.org/docs/GetElementPtr.html#what-s-an-uglygep) to make the IR
+ // prettier and more alias analysis friendly. One caveat: if the original GEP
+ // ends with a StructType, we need to split the GEP at the last
+ // SequentialType. For instance, consider the following IR:
+ //
+ // %struct.S = type { float, double }
+ // @array = global [1024 x %struct.S]
+ // %p = getelementptr %array, 0, %i + 5, 1
+ //
+ // To separate the constant 5 from %p, we would need to split %p at the last
+ // array index so that we have:
+ //
+ // %addr = gep %array, 0, %i
+ // %p = gep %addr, 5, 1
+ Instruction *NewGEP = GEP->clone();
+ NewGEP->insertBefore(GEP);
+ Type *IntPtrTy = DL->getIntPtrType(GEP->getType());
+ Value *Addr = new PtrToIntInst(NewGEP, IntPtrTy, "", GEP);
+ Addr = BinaryOperator::CreateAdd(
+ Addr, ConstantInt::get(IntPtrTy, AccumulativeByteOffset, true), "", GEP);
+ Addr = new IntToPtrInst(Addr, GEP->getType(), "", GEP);
+
+ GEP->replaceAllUsesWith(Addr);
+ GEP->eraseFromParent();
+
+ return true;
+}
+
+bool SeparateConstOffsetFromGEP::runOnFunction(Function &F) {
+ if (DisableSeparateConstOffsetFromGEP)
+ return false;
+
+ bool Changed = false;
+ for (Function::iterator B = F.begin(), BE = F.end(); B != BE; ++B) {
+ for (BasicBlock::iterator I = B->begin(), IE = B->end(); I != IE; ) {
+ if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(I++)) {
+ Changed |= splitGEP(GEP);
+ }
+ // No need to split GEP ConstantExprs because all its indices are constant
+ // already.
+ }
+ }
+ return Changed;
+}
Added: llvm/trunk/test/Transforms/SeparateConstOffsetFromGEP/NVPTX/lit.local.cfg
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/SeparateConstOffsetFromGEP/NVPTX/lit.local.cfg?rev=207783&view=auto
==============================================================================
--- llvm/trunk/test/Transforms/SeparateConstOffsetFromGEP/NVPTX/lit.local.cfg (added)
+++ llvm/trunk/test/Transforms/SeparateConstOffsetFromGEP/NVPTX/lit.local.cfg Thu May 1 13:38:36 2014
@@ -0,0 +1,4 @@
+targets = set(config.root.targets_to_build.split())
+if not 'NVPTX' in targets:
+ config.unsupported = True
+
Added: llvm/trunk/test/Transforms/SeparateConstOffsetFromGEP/NVPTX/split-gep-and-gvn.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/SeparateConstOffsetFromGEP/NVPTX/split-gep-and-gvn.ll?rev=207783&view=auto
==============================================================================
--- llvm/trunk/test/Transforms/SeparateConstOffsetFromGEP/NVPTX/split-gep-and-gvn.ll (added)
+++ llvm/trunk/test/Transforms/SeparateConstOffsetFromGEP/NVPTX/split-gep-and-gvn.ll Thu May 1 13:38:36 2014
@@ -0,0 +1,60 @@
+; RUN: llc < %s -march=nvptx -mcpu=sm_20 | FileCheck %s --check-prefix=PTX
+; RUN: llc < %s -march=nvptx64 -mcpu=sm_20 | FileCheck %s --check-prefix=PTX
+; RUN: opt < %s -S -separate-const-offset-from-gep -gvn -dce | FileCheck %s --check-prefix=IR
+
+; Verifies the SeparateConstOffsetFromGEP pass.
+; The following code computes
+; *output = array[x][y] + array[x][y+1] + array[x+1][y] + array[x+1][y+1]
+;
+; We expect SeparateConstOffsetFromGEP to transform it to
+;
+; float *base = &a[x][y];
+; *output = base[0] + base[1] + base[32] + base[33];
+;
+; so the backend can emit PTX that uses fewer virtual registers.
+
+target datalayout = "e-i64:64-v16:16-v32:32-n16:32:64"
+target triple = "nvptx64-unknown-unknown"
+
+ at array = internal addrspace(3) constant [32 x [32 x float]] zeroinitializer, align 4
+
+define void @sum_of_array(i32 %x, i32 %y, float* nocapture %output) {
+.preheader:
+ %0 = zext i32 %y to i64
+ %1 = zext i32 %x to i64
+ %2 = getelementptr inbounds [32 x [32 x float]] addrspace(3)* @array, i64 0, i64 %1, i64 %0
+ %3 = addrspacecast float addrspace(3)* %2 to float*
+ %4 = load float* %3, align 4
+ %5 = fadd float %4, 0.000000e+00
+ %6 = add i32 %y, 1
+ %7 = zext i32 %6 to i64
+ %8 = getelementptr inbounds [32 x [32 x float]] addrspace(3)* @array, i64 0, i64 %1, i64 %7
+ %9 = addrspacecast float addrspace(3)* %8 to float*
+ %10 = load float* %9, align 4
+ %11 = fadd float %5, %10
+ %12 = add i32 %x, 1
+ %13 = zext i32 %12 to i64
+ %14 = getelementptr inbounds [32 x [32 x float]] addrspace(3)* @array, i64 0, i64 %13, i64 %0
+ %15 = addrspacecast float addrspace(3)* %14 to float*
+ %16 = load float* %15, align 4
+ %17 = fadd float %11, %16
+ %18 = getelementptr inbounds [32 x [32 x float]] addrspace(3)* @array, i64 0, i64 %13, i64 %7
+ %19 = addrspacecast float addrspace(3)* %18 to float*
+ %20 = load float* %19, align 4
+ %21 = fadd float %17, %20
+ store float %21, float* %output, align 4
+ ret void
+}
+
+; PTX-LABEL: sum_of_array(
+; PTX: ld.shared.f32 {{%f[0-9]+}}, {{\[}}[[BASE_REG:%(rl|r)[0-9]+]]{{\]}}
+; PTX: ld.shared.f32 {{%f[0-9]+}}, {{\[}}[[BASE_REG]]+4{{\]}}
+; PTX: ld.shared.f32 {{%f[0-9]+}}, {{\[}}[[BASE_REG]]+128{{\]}}
+; PTX: ld.shared.f32 {{%f[0-9]+}}, {{\[}}[[BASE_REG]]+132{{\]}}
+
+; IR-LABEL: @sum_of_array(
+; IR: [[BASE_PTR:%[0-9]+]] = getelementptr inbounds [32 x [32 x float]] addrspace(3)* @array, i64 0, i32 %x, i32 %y
+; IR: [[BASE_INT:%[0-9]+]] = ptrtoint float addrspace(3)* [[BASE_PTR]] to i64
+; IR: %5 = add i64 [[BASE_INT]], 4
+; IR: %10 = add i64 [[BASE_INT]], 128
+; IR: %15 = add i64 [[BASE_INT]], 132
Added: llvm/trunk/test/Transforms/SeparateConstOffsetFromGEP/NVPTX/split-gep.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/SeparateConstOffsetFromGEP/NVPTX/split-gep.ll?rev=207783&view=auto
==============================================================================
--- llvm/trunk/test/Transforms/SeparateConstOffsetFromGEP/NVPTX/split-gep.ll (added)
+++ llvm/trunk/test/Transforms/SeparateConstOffsetFromGEP/NVPTX/split-gep.ll Thu May 1 13:38:36 2014
@@ -0,0 +1,101 @@
+; RUN: opt < %s -separate-const-offset-from-gep -dce -S | FileCheck %s
+
+; Several unit tests for -separate-const-offset-from-gep. The transformation
+; heavily relies on TargetTransformInfo, so we put these tests under
+; target-specific folders.
+
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+; target triple is necessary; otherwise TargetTransformInfo rejects any
+; addressing mode.
+target triple = "nvptx64-unknown-unknown"
+
+%struct.S = type { float, double }
+
+ at struct_array = global [1024 x %struct.S] zeroinitializer, align 16
+ at float_2d_array = global [32 x [32 x float]] zeroinitializer, align 4
+
+; We should not extract any struct field indices, because fields in a struct
+; may have different types.
+define double* @struct(i32 %i) {
+entry:
+ %add = add nsw i32 %i, 5
+ %idxprom = sext i32 %add to i64
+ %p = getelementptr inbounds [1024 x %struct.S]* @struct_array, i64 0, i64 %idxprom, i32 1
+ ret double* %p
+}
+; CHECK-LABEL: @struct
+; CHECK: getelementptr [1024 x %struct.S]* @struct_array, i64 0, i32 %i, i32 1
+
+; We should be able to trace into sext/zext if it's directly used as a GEP
+; index.
+define float* @sext_zext(i32 %i, i32 %j) {
+entry:
+ %i1 = add i32 %i, 1
+ %j2 = add i32 %j, 2
+ %i1.ext = sext i32 %i1 to i64
+ %j2.ext = zext i32 %j2 to i64
+ %p = getelementptr inbounds [32 x [32 x float]]* @float_2d_array, i64 0, i64 %i1.ext, i64 %j2.ext
+ ret float* %p
+}
+; CHECK-LABEL: @sext_zext
+; CHECK: getelementptr [32 x [32 x float]]* @float_2d_array, i64 0, i32 %i, i32 %j
+; CHECK: add i64 %{{[0-9]+}}, 136
+
+; We should be able to trace into sext/zext if it can be distributed to both
+; operands, e.g., sext (add nsw a, b) == add nsw (sext a), (sext b)
+define float* @ext_add_no_overflow(i64 %a, i32 %b, i64 %c, i32 %d) {
+ %b1 = add nsw i32 %b, 1
+ %b2 = sext i32 %b1 to i64
+ %i = add i64 %a, %b2
+ %d1 = add nuw i32 %d, 1
+ %d2 = zext i32 %d1 to i64
+ %j = add i64 %c, %d2
+ %p = getelementptr inbounds [32 x [32 x float]]* @float_2d_array, i64 0, i64 %i, i64 %j
+ ret float* %p
+}
+; CHECK-LABEL: @ext_add_no_overflow
+; CHECK: [[BASE_PTR:%[0-9]+]] = getelementptr [32 x [32 x float]]* @float_2d_array, i64 0, i64 %{{[0-9]+}}, i64 %{{[0-9]+}}
+; CHECK: [[BASE_INT:%[0-9]+]] = ptrtoint float* [[BASE_PTR]] to i64
+; CHECK: add i64 [[BASE_INT]], 132
+
+; We should treat "or" with no common bits (%k) as "add", and leave "or" with
+; potentially common bits (%l) as is.
+define float* @or(i64 %i) {
+entry:
+ %j = shl i64 %i, 2
+ %k = or i64 %j, 3 ; no common bits
+ %l = or i64 %j, 4 ; potentially common bits
+ %p = getelementptr inbounds [32 x [32 x float]]* @float_2d_array, i64 0, i64 %k, i64 %l
+ ret float* %p
+}
+; CHECK-LABEL: @or
+; CHECK: getelementptr [32 x [32 x float]]* @float_2d_array, i64 0, i64 %j, i64 %l
+; CHECK: add i64 %{{[0-9]+}}, 384
+
+; The subexpression (b + 5) is used in both "i = a + (b + 5)" and "*out = b +
+; 5". When extracting the constant offset 5, make sure "*out = b + 5" isn't
+; affected.
+define float* @expr(i64 %a, i64 %b, i64* %out) {
+entry:
+ %b5 = add i64 %b, 5
+ %i = add i64 %b5, %a
+ %p = getelementptr inbounds [32 x [32 x float]]* @float_2d_array, i64 0, i64 %i, i64 0
+ store i64 %b5, i64* %out
+ ret float* %p
+}
+; CHECK-LABEL: @expr
+; CHECK: getelementptr [32 x [32 x float]]* @float_2d_array, i64 0, i64 %0, i64 0
+; CHECK: add i64 %{{[0-9]+}}, 640
+; CHECK: store i64 %b5, i64* %out
+
+; Verifies we handle "sub" correctly.
+define float* @sub(i64 %i, i64 %j) {
+ %i2 = sub i64 %i, 5 ; i - 5
+ %j2 = sub i64 5, %j ; 5 - i
+ %p = getelementptr inbounds [32 x [32 x float]]* @float_2d_array, i64 0, i64 %i2, i64 %j2
+ ret float* %p
+}
+; CHECK-LABEL: @sub
+; CHECK: %[[j2:[0-9]+]] = sub i64 0, %j
+; CHECK: getelementptr [32 x [32 x float]]* @float_2d_array, i64 0, i64 %i, i64 %[[j2]]
+; CHECK: add i64 %{{[0-9]+}}, -620
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