[llvm-commits] [llvm] r92709 - in /llvm/trunk/lib/Transforms/InstCombine: CMakeLists.txt InstCombineShifts.cpp
Chris Lattner
sabre at nondot.org
Mon Jan 4 23:44:46 PST 2010
Author: lattner
Date: Tue Jan 5 01:44:46 2010
New Revision: 92709
URL: http://llvm.org/viewvc/llvm-project?rev=92709&view=rev
Log:
split instcombine of shifts out to its own file.
Added:
llvm/trunk/lib/Transforms/InstCombine/InstCombineShifts.cpp
Modified:
llvm/trunk/lib/Transforms/InstCombine/CMakeLists.txt
Modified: llvm/trunk/lib/Transforms/InstCombine/CMakeLists.txt
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/InstCombine/CMakeLists.txt?rev=92709&r1=92708&r2=92709&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/InstCombine/CMakeLists.txt (original)
+++ llvm/trunk/lib/Transforms/InstCombine/CMakeLists.txt Tue Jan 5 01:44:46 2010
@@ -8,6 +8,7 @@
InstCombineMulDivRem.cpp
InstCombinePHI.cpp
InstCombineSelect.cpp
+ InstCombineShifts.cpp
InstCombineSimplifyDemanded.cpp
InstCombineVectorOps.cpp
)
Added: llvm/trunk/lib/Transforms/InstCombine/InstCombineShifts.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/InstCombine/InstCombineShifts.cpp?rev=92709&view=auto
==============================================================================
--- llvm/trunk/lib/Transforms/InstCombine/InstCombineShifts.cpp (added)
+++ llvm/trunk/lib/Transforms/InstCombine/InstCombineShifts.cpp Tue Jan 5 01:44:46 2010
@@ -0,0 +1,436 @@
+//===- InstCombineShifts.cpp ----------------------------------------------===//
+//
+// The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file implements the visitShl, visitLShr, and visitAShr functions.
+//
+//===----------------------------------------------------------------------===//
+
+#include "InstCombine.h"
+#include "llvm/Support/PatternMatch.h"
+using namespace llvm;
+using namespace PatternMatch;
+
+Instruction *InstCombiner::commonShiftTransforms(BinaryOperator &I) {
+ assert(I.getOperand(1)->getType() == I.getOperand(0)->getType());
+ Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
+
+ // shl X, 0 == X and shr X, 0 == X
+ // shl 0, X == 0 and shr 0, X == 0
+ if (Op1 == Constant::getNullValue(Op1->getType()) ||
+ Op0 == Constant::getNullValue(Op0->getType()))
+ return ReplaceInstUsesWith(I, Op0);
+
+ if (isa<UndefValue>(Op0)) {
+ if (I.getOpcode() == Instruction::AShr) // undef >>s X -> undef
+ return ReplaceInstUsesWith(I, Op0);
+ else // undef << X -> 0, undef >>u X -> 0
+ return ReplaceInstUsesWith(I, Constant::getNullValue(I.getType()));
+ }
+ if (isa<UndefValue>(Op1)) {
+ if (I.getOpcode() == Instruction::AShr) // X >>s undef -> X
+ return ReplaceInstUsesWith(I, Op0);
+ else // X << undef, X >>u undef -> 0
+ return ReplaceInstUsesWith(I, Constant::getNullValue(I.getType()));
+ }
+
+ // See if we can fold away this shift.
+ if (SimplifyDemandedInstructionBits(I))
+ return &I;
+
+ // Try to fold constant and into select arguments.
+ if (isa<Constant>(Op0))
+ if (SelectInst *SI = dyn_cast<SelectInst>(Op1))
+ if (Instruction *R = FoldOpIntoSelect(I, SI))
+ return R;
+
+ if (ConstantInt *CUI = dyn_cast<ConstantInt>(Op1))
+ if (Instruction *Res = FoldShiftByConstant(Op0, CUI, I))
+ return Res;
+ return 0;
+}
+
+Instruction *InstCombiner::FoldShiftByConstant(Value *Op0, ConstantInt *Op1,
+ BinaryOperator &I) {
+ bool isLeftShift = I.getOpcode() == Instruction::Shl;
+
+ // See if we can simplify any instructions used by the instruction whose sole
+ // purpose is to compute bits we don't care about.
+ uint32_t TypeBits = Op0->getType()->getScalarSizeInBits();
+
+ // shl i32 X, 32 = 0 and srl i8 Y, 9 = 0, ... just don't eliminate
+ // a signed shift.
+ //
+ if (Op1->uge(TypeBits)) {
+ if (I.getOpcode() != Instruction::AShr)
+ return ReplaceInstUsesWith(I, Constant::getNullValue(Op0->getType()));
+ else {
+ I.setOperand(1, ConstantInt::get(I.getType(), TypeBits-1));
+ return &I;
+ }
+ }
+
+ // ((X*C1) << C2) == (X * (C1 << C2))
+ if (BinaryOperator *BO = dyn_cast<BinaryOperator>(Op0))
+ if (BO->getOpcode() == Instruction::Mul && isLeftShift)
+ if (Constant *BOOp = dyn_cast<Constant>(BO->getOperand(1)))
+ return BinaryOperator::CreateMul(BO->getOperand(0),
+ ConstantExpr::getShl(BOOp, Op1));
+
+ // Try to fold constant and into select arguments.
+ if (SelectInst *SI = dyn_cast<SelectInst>(Op0))
+ if (Instruction *R = FoldOpIntoSelect(I, SI))
+ return R;
+ if (isa<PHINode>(Op0))
+ if (Instruction *NV = FoldOpIntoPhi(I))
+ return NV;
+
+ // Fold shift2(trunc(shift1(x,c1)), c2) -> trunc(shift2(shift1(x,c1),c2))
+ if (TruncInst *TI = dyn_cast<TruncInst>(Op0)) {
+ Instruction *TrOp = dyn_cast<Instruction>(TI->getOperand(0));
+ // If 'shift2' is an ashr, we would have to get the sign bit into a funny
+ // place. Don't try to do this transformation in this case. Also, we
+ // require that the input operand is a shift-by-constant so that we have
+ // confidence that the shifts will get folded together. We could do this
+ // xform in more cases, but it is unlikely to be profitable.
+ if (TrOp && I.isLogicalShift() && TrOp->isShift() &&
+ isa<ConstantInt>(TrOp->getOperand(1))) {
+ // Okay, we'll do this xform. Make the shift of shift.
+ Constant *ShAmt = ConstantExpr::getZExt(Op1, TrOp->getType());
+ // (shift2 (shift1 & 0x00FF), c2)
+ Value *NSh = Builder->CreateBinOp(I.getOpcode(), TrOp, ShAmt,I.getName());
+
+ // For logical shifts, the truncation has the effect of making the high
+ // part of the register be zeros. Emulate this by inserting an AND to
+ // clear the top bits as needed. This 'and' will usually be zapped by
+ // other xforms later if dead.
+ unsigned SrcSize = TrOp->getType()->getScalarSizeInBits();
+ unsigned DstSize = TI->getType()->getScalarSizeInBits();
+ APInt MaskV(APInt::getLowBitsSet(SrcSize, DstSize));
+
+ // The mask we constructed says what the trunc would do if occurring
+ // between the shifts. We want to know the effect *after* the second
+ // shift. We know that it is a logical shift by a constant, so adjust the
+ // mask as appropriate.
+ if (I.getOpcode() == Instruction::Shl)
+ MaskV <<= Op1->getZExtValue();
+ else {
+ assert(I.getOpcode() == Instruction::LShr && "Unknown logical shift");
+ MaskV = MaskV.lshr(Op1->getZExtValue());
+ }
+
+ // shift1 & 0x00FF
+ Value *And = Builder->CreateAnd(NSh,
+ ConstantInt::get(I.getContext(), MaskV),
+ TI->getName());
+
+ // Return the value truncated to the interesting size.
+ return new TruncInst(And, I.getType());
+ }
+ }
+
+ if (Op0->hasOneUse()) {
+ if (BinaryOperator *Op0BO = dyn_cast<BinaryOperator>(Op0)) {
+ // Turn ((X >> C) + Y) << C -> (X + (Y << C)) & (~0 << C)
+ Value *V1, *V2;
+ ConstantInt *CC;
+ switch (Op0BO->getOpcode()) {
+ default: break;
+ case Instruction::Add:
+ case Instruction::And:
+ case Instruction::Or:
+ case Instruction::Xor: {
+ // These operators commute.
+ // Turn (Y + (X >> C)) << C -> (X + (Y << C)) & (~0 << C)
+ if (isLeftShift && Op0BO->getOperand(1)->hasOneUse() &&
+ match(Op0BO->getOperand(1), m_Shr(m_Value(V1),
+ m_Specific(Op1)))) {
+ Value *YS = // (Y << C)
+ Builder->CreateShl(Op0BO->getOperand(0), Op1, Op0BO->getName());
+ // (X + (Y << C))
+ Value *X = Builder->CreateBinOp(Op0BO->getOpcode(), YS, V1,
+ Op0BO->getOperand(1)->getName());
+ uint32_t Op1Val = Op1->getLimitedValue(TypeBits);
+ return BinaryOperator::CreateAnd(X, ConstantInt::get(I.getContext(),
+ APInt::getHighBitsSet(TypeBits, TypeBits-Op1Val)));
+ }
+
+ // Turn (Y + ((X >> C) & CC)) << C -> ((X & (CC << C)) + (Y << C))
+ Value *Op0BOOp1 = Op0BO->getOperand(1);
+ if (isLeftShift && Op0BOOp1->hasOneUse() &&
+ match(Op0BOOp1,
+ m_And(m_Shr(m_Value(V1), m_Specific(Op1)),
+ m_ConstantInt(CC))) &&
+ cast<BinaryOperator>(Op0BOOp1)->getOperand(0)->hasOneUse()) {
+ Value *YS = // (Y << C)
+ Builder->CreateShl(Op0BO->getOperand(0), Op1,
+ Op0BO->getName());
+ // X & (CC << C)
+ Value *XM = Builder->CreateAnd(V1, ConstantExpr::getShl(CC, Op1),
+ V1->getName()+".mask");
+ return BinaryOperator::Create(Op0BO->getOpcode(), YS, XM);
+ }
+ }
+
+ // FALL THROUGH.
+ case Instruction::Sub: {
+ // Turn ((X >> C) + Y) << C -> (X + (Y << C)) & (~0 << C)
+ if (isLeftShift && Op0BO->getOperand(0)->hasOneUse() &&
+ match(Op0BO->getOperand(0), m_Shr(m_Value(V1),
+ m_Specific(Op1)))) {
+ Value *YS = // (Y << C)
+ Builder->CreateShl(Op0BO->getOperand(1), Op1, Op0BO->getName());
+ // (X + (Y << C))
+ Value *X = Builder->CreateBinOp(Op0BO->getOpcode(), V1, YS,
+ Op0BO->getOperand(0)->getName());
+ uint32_t Op1Val = Op1->getLimitedValue(TypeBits);
+ return BinaryOperator::CreateAnd(X, ConstantInt::get(I.getContext(),
+ APInt::getHighBitsSet(TypeBits, TypeBits-Op1Val)));
+ }
+
+ // Turn (((X >> C)&CC) + Y) << C -> (X + (Y << C)) & (CC << C)
+ if (isLeftShift && Op0BO->getOperand(0)->hasOneUse() &&
+ match(Op0BO->getOperand(0),
+ m_And(m_Shr(m_Value(V1), m_Value(V2)),
+ m_ConstantInt(CC))) && V2 == Op1 &&
+ cast<BinaryOperator>(Op0BO->getOperand(0))
+ ->getOperand(0)->hasOneUse()) {
+ Value *YS = // (Y << C)
+ Builder->CreateShl(Op0BO->getOperand(1), Op1, Op0BO->getName());
+ // X & (CC << C)
+ Value *XM = Builder->CreateAnd(V1, ConstantExpr::getShl(CC, Op1),
+ V1->getName()+".mask");
+
+ return BinaryOperator::Create(Op0BO->getOpcode(), XM, YS);
+ }
+
+ break;
+ }
+ }
+
+
+ // If the operand is an bitwise operator with a constant RHS, and the
+ // shift is the only use, we can pull it out of the shift.
+ if (ConstantInt *Op0C = dyn_cast<ConstantInt>(Op0BO->getOperand(1))) {
+ bool isValid = true; // Valid only for And, Or, Xor
+ bool highBitSet = false; // Transform if high bit of constant set?
+
+ switch (Op0BO->getOpcode()) {
+ default: isValid = false; break; // Do not perform transform!
+ case Instruction::Add:
+ isValid = isLeftShift;
+ break;
+ case Instruction::Or:
+ case Instruction::Xor:
+ highBitSet = false;
+ break;
+ case Instruction::And:
+ highBitSet = true;
+ break;
+ }
+
+ // If this is a signed shift right, and the high bit is modified
+ // by the logical operation, do not perform the transformation.
+ // The highBitSet boolean indicates the value of the high bit of
+ // the constant which would cause it to be modified for this
+ // operation.
+ //
+ if (isValid && I.getOpcode() == Instruction::AShr)
+ isValid = Op0C->getValue()[TypeBits-1] == highBitSet;
+
+ if (isValid) {
+ Constant *NewRHS = ConstantExpr::get(I.getOpcode(), Op0C, Op1);
+
+ Value *NewShift =
+ Builder->CreateBinOp(I.getOpcode(), Op0BO->getOperand(0), Op1);
+ NewShift->takeName(Op0BO);
+
+ return BinaryOperator::Create(Op0BO->getOpcode(), NewShift,
+ NewRHS);
+ }
+ }
+ }
+ }
+
+ // Find out if this is a shift of a shift by a constant.
+ BinaryOperator *ShiftOp = dyn_cast<BinaryOperator>(Op0);
+ if (ShiftOp && !ShiftOp->isShift())
+ ShiftOp = 0;
+
+ if (ShiftOp && isa<ConstantInt>(ShiftOp->getOperand(1))) {
+ ConstantInt *ShiftAmt1C = cast<ConstantInt>(ShiftOp->getOperand(1));
+ uint32_t ShiftAmt1 = ShiftAmt1C->getLimitedValue(TypeBits);
+ uint32_t ShiftAmt2 = Op1->getLimitedValue(TypeBits);
+ assert(ShiftAmt2 != 0 && "Should have been simplified earlier");
+ if (ShiftAmt1 == 0) return 0; // Will be simplified in the future.
+ Value *X = ShiftOp->getOperand(0);
+
+ uint32_t AmtSum = ShiftAmt1+ShiftAmt2; // Fold into one big shift.
+
+ const IntegerType *Ty = cast<IntegerType>(I.getType());
+
+ // Check for (X << c1) << c2 and (X >> c1) >> c2
+ if (I.getOpcode() == ShiftOp->getOpcode()) {
+ // If this is oversized composite shift, then unsigned shifts get 0, ashr
+ // saturates.
+ if (AmtSum >= TypeBits) {
+ if (I.getOpcode() != Instruction::AShr)
+ return ReplaceInstUsesWith(I, Constant::getNullValue(I.getType()));
+ AmtSum = TypeBits-1; // Saturate to 31 for i32 ashr.
+ }
+
+ return BinaryOperator::Create(I.getOpcode(), X,
+ ConstantInt::get(Ty, AmtSum));
+ }
+
+ if (ShiftOp->getOpcode() == Instruction::LShr &&
+ I.getOpcode() == Instruction::AShr) {
+ if (AmtSum >= TypeBits)
+ return ReplaceInstUsesWith(I, Constant::getNullValue(I.getType()));
+
+ // ((X >>u C1) >>s C2) -> (X >>u (C1+C2)) since C1 != 0.
+ return BinaryOperator::CreateLShr(X, ConstantInt::get(Ty, AmtSum));
+ }
+
+ if (ShiftOp->getOpcode() == Instruction::AShr &&
+ I.getOpcode() == Instruction::LShr) {
+ // ((X >>s C1) >>u C2) -> ((X >>s (C1+C2)) & mask) since C1 != 0.
+ if (AmtSum >= TypeBits)
+ AmtSum = TypeBits-1;
+
+ Value *Shift = Builder->CreateAShr(X, ConstantInt::get(Ty, AmtSum));
+
+ APInt Mask(APInt::getLowBitsSet(TypeBits, TypeBits - ShiftAmt2));
+ return BinaryOperator::CreateAnd(Shift,
+ ConstantInt::get(I.getContext(), Mask));
+ }
+
+ // Okay, if we get here, one shift must be left, and the other shift must be
+ // right. See if the amounts are equal.
+ if (ShiftAmt1 == ShiftAmt2) {
+ // If we have ((X >>? C) << C), turn this into X & (-1 << C).
+ if (I.getOpcode() == Instruction::Shl) {
+ APInt Mask(APInt::getHighBitsSet(TypeBits, TypeBits - ShiftAmt1));
+ return BinaryOperator::CreateAnd(X,
+ ConstantInt::get(I.getContext(),Mask));
+ }
+ // If we have ((X << C) >>u C), turn this into X & (-1 >>u C).
+ if (I.getOpcode() == Instruction::LShr) {
+ APInt Mask(APInt::getLowBitsSet(TypeBits, TypeBits - ShiftAmt1));
+ return BinaryOperator::CreateAnd(X,
+ ConstantInt::get(I.getContext(), Mask));
+ }
+ // We can simplify ((X << C) >>s C) into a trunc + sext.
+ // NOTE: we could do this for any C, but that would make 'unusual' integer
+ // types. For now, just stick to ones well-supported by the code
+ // generators.
+ const Type *SExtType = 0;
+ switch (Ty->getBitWidth() - ShiftAmt1) {
+ case 1 :
+ case 8 :
+ case 16 :
+ case 32 :
+ case 64 :
+ case 128:
+ SExtType = IntegerType::get(I.getContext(),
+ Ty->getBitWidth() - ShiftAmt1);
+ break;
+ default: break;
+ }
+ if (SExtType)
+ return new SExtInst(Builder->CreateTrunc(X, SExtType, "sext"), Ty);
+ // Otherwise, we can't handle it yet.
+ } else if (ShiftAmt1 < ShiftAmt2) {
+ uint32_t ShiftDiff = ShiftAmt2-ShiftAmt1;
+
+ // (X >>? C1) << C2 --> X << (C2-C1) & (-1 << C2)
+ if (I.getOpcode() == Instruction::Shl) {
+ assert(ShiftOp->getOpcode() == Instruction::LShr ||
+ ShiftOp->getOpcode() == Instruction::AShr);
+ Value *Shift = Builder->CreateShl(X, ConstantInt::get(Ty, ShiftDiff));
+
+ APInt Mask(APInt::getHighBitsSet(TypeBits, TypeBits - ShiftAmt2));
+ return BinaryOperator::CreateAnd(Shift,
+ ConstantInt::get(I.getContext(),Mask));
+ }
+
+ // (X << C1) >>u C2 --> X >>u (C2-C1) & (-1 >> C2)
+ if (I.getOpcode() == Instruction::LShr) {
+ assert(ShiftOp->getOpcode() == Instruction::Shl);
+ Value *Shift = Builder->CreateLShr(X, ConstantInt::get(Ty, ShiftDiff));
+
+ APInt Mask(APInt::getLowBitsSet(TypeBits, TypeBits - ShiftAmt2));
+ return BinaryOperator::CreateAnd(Shift,
+ ConstantInt::get(I.getContext(),Mask));
+ }
+
+ // We can't handle (X << C1) >>s C2, it shifts arbitrary bits in.
+ } else {
+ assert(ShiftAmt2 < ShiftAmt1);
+ uint32_t ShiftDiff = ShiftAmt1-ShiftAmt2;
+
+ // (X >>? C1) << C2 --> X >>? (C1-C2) & (-1 << C2)
+ if (I.getOpcode() == Instruction::Shl) {
+ assert(ShiftOp->getOpcode() == Instruction::LShr ||
+ ShiftOp->getOpcode() == Instruction::AShr);
+ Value *Shift = Builder->CreateBinOp(ShiftOp->getOpcode(), X,
+ ConstantInt::get(Ty, ShiftDiff));
+
+ APInt Mask(APInt::getHighBitsSet(TypeBits, TypeBits - ShiftAmt2));
+ return BinaryOperator::CreateAnd(Shift,
+ ConstantInt::get(I.getContext(),Mask));
+ }
+
+ // (X << C1) >>u C2 --> X << (C1-C2) & (-1 >> C2)
+ if (I.getOpcode() == Instruction::LShr) {
+ assert(ShiftOp->getOpcode() == Instruction::Shl);
+ Value *Shift = Builder->CreateShl(X, ConstantInt::get(Ty, ShiftDiff));
+
+ APInt Mask(APInt::getLowBitsSet(TypeBits, TypeBits - ShiftAmt2));
+ return BinaryOperator::CreateAnd(Shift,
+ ConstantInt::get(I.getContext(),Mask));
+ }
+
+ // We can't handle (X << C1) >>a C2, it shifts arbitrary bits in.
+ }
+ }
+ return 0;
+}
+
+Instruction *InstCombiner::visitShl(BinaryOperator &I) {
+ return commonShiftTransforms(I);
+}
+
+Instruction *InstCombiner::visitLShr(BinaryOperator &I) {
+ return commonShiftTransforms(I);
+}
+
+Instruction *InstCombiner::visitAShr(BinaryOperator &I) {
+ if (Instruction *R = commonShiftTransforms(I))
+ return R;
+
+ Value *Op0 = I.getOperand(0);
+
+ // ashr int -1, X = -1 (for any arithmetic shift rights of ~0)
+ if (ConstantInt *CSI = dyn_cast<ConstantInt>(Op0))
+ if (CSI->isAllOnesValue())
+ return ReplaceInstUsesWith(I, CSI);
+
+ // See if we can turn a signed shr into an unsigned shr.
+ if (MaskedValueIsZero(Op0,
+ APInt::getSignBit(I.getType()->getScalarSizeInBits())))
+ return BinaryOperator::CreateLShr(Op0, I.getOperand(1));
+
+ // Arithmetic shifting an all-sign-bit value is a no-op.
+ unsigned NumSignBits = ComputeNumSignBits(Op0);
+ if (NumSignBits == Op0->getType()->getScalarSizeInBits())
+ return ReplaceInstUsesWith(I, Op0);
+
+ return 0;
+}
+
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