split instcombine of shifts out to its own file.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@92709 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 436 insertions, 0 deletions

diff --git a/lib/Transforms/InstCombine/InstCombineShifts.cpp b/lib/Transforms/InstCombine/InstCombineShifts.cpp
new file mode 100644
index 0000000000..404fcecc33
--- /dev/null
+++ b/lib/Transforms/InstCombine/InstCombineShifts.cpp
@@ -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;
+}
+