refactor some code out into a helper method.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@125451 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Transforms/InstCombine/InstCombine.h

@@ -145,6 +145,8 @@ public:
                                               ConstantInt *RHS);
   Instruction *FoldICmpDivCst(ICmpInst &ICI, BinaryOperator *DivI,
                               ConstantInt *DivRHS);
+  Instruction *FoldICmpShrCst(ICmpInst &ICI, BinaryOperator *DivI,
+                              ConstantInt *DivRHS);
   Instruction *FoldICmpAddOpCst(ICmpInst &ICI, Value *X, ConstantInt *CI,
                                 ICmpInst::Predicate Pred, Value *TheAdd);
   Instruction *FoldGEPICmp(GEPOperator *GEPLHS, Value *RHS,

lib/Transforms/InstCombine/InstCombineCompares.cpp

@@ -928,6 +928,55 @@ Instruction *InstCombiner::FoldICmpDivCst(ICmpInst &ICI, BinaryOperator *DivI,
   }
 }
 
+/// FoldICmpShrCst - Handle "icmp(([al]shr X, cst1), cst2)".
+Instruction *InstCombiner::FoldICmpShrCst(ICmpInst &ICI, BinaryOperator *Shr,
+                                          ConstantInt *ShAmt) {
+  if (!ICI.isEquality()) return 0;
+
+  const APInt &CmpRHSV = cast<ConstantInt>(ICI.getOperand(1))->getValue();
+  
+  // Check that the shift amount is in range.  If not, don't perform
+  // undefined shifts.  When the shift is visited it will be
+  // simplified.
+  uint32_t TypeBits = CmpRHSV.getBitWidth();
+  uint32_t ShAmtVal = (uint32_t)ShAmt->getLimitedValue(TypeBits);
+  if (ShAmtVal >= TypeBits)
+    return 0;
+  
+  // If we are comparing against bits always shifted out, the
+  // comparison cannot succeed.
+  APInt Comp = CmpRHSV << ShAmtVal;
+  ConstantInt *ShiftedCmpRHS = ConstantInt::get(ICI.getContext(), Comp);
+  if (Shr->getOpcode() == Instruction::LShr)
+    Comp = Comp.lshr(ShAmtVal);
+  else
+    Comp = Comp.ashr(ShAmtVal);
+  
+  if (Comp != CmpRHSV) { // Comparing against a bit that we know is zero.
+    bool IsICMP_NE = ICI.getPredicate() == ICmpInst::ICMP_NE;
+    Constant *Cst = ConstantInt::get(Type::getInt1Ty(ICI.getContext()),
+                                     IsICMP_NE);
+    return ReplaceInstUsesWith(ICI, Cst);
+  }
+  
+  // Otherwise, check to see if the bits shifted out are known to be zero.
+  // If so, we can compare against the unshifted value:
+  //  (X & 4) >> 1 == 2  --> (X & 4) == 4.
+  if (Shr->hasOneUse() && cast<BinaryOperator>(Shr)->isExact())
+    return new ICmpInst(ICI.getPredicate(), Shr->getOperand(0), ShiftedCmpRHS);
+  
+  if (Shr->hasOneUse()) {
+    // Otherwise strength reduce the shift into an and.
+    APInt Val(APInt::getHighBitsSet(TypeBits, TypeBits - ShAmtVal));
+    Constant *Mask = ConstantInt::get(ICI.getContext(), Val);
+    
+    Value *And = Builder->CreateAnd(Shr->getOperand(0),
+                                    Mask, Shr->getName()+".mask");
+    return new ICmpInst(ICI.getPredicate(), And, ShiftedCmpRHS);
+  }
+  return 0;
+}
+
 
 /// visitICmpInstWithInstAndIntCst - Handle "icmp (instr, intcst)".
 ///
@@ -1153,7 +1202,6 @@ Instruction *InstCombiner::visitICmpInstWithInstAndIntCst(ICmpInst &ICI,
     if (match(LHSI, m_Or(m_PtrToInt(m_Value(P)), m_PtrToInt(m_Value(Q))))) {
       // Simplify icmp eq (or (ptrtoint P), (ptrtoint Q)), 0
       // -> and (icmp eq P, null), (icmp eq Q, null).
-
       Value *ICIP = Builder->CreateICmp(ICI.getPredicate(), P,
                                         Constant::getNullValue(P->getType()));
       Value *ICIQ = Builder->CreateICmp(ICI.getPredicate(), Q,
@@ -1229,54 +1277,14 @@ Instruction *InstCombiner::visitICmpInstWithInstAndIntCst(ICmpInst &ICI,
   }
     
   case Instruction::LShr:         // (icmp pred (shr X, ShAmt), CI)
-  case Instruction::AShr: {
+  case Instruction::AShr:
     // Only handle equality comparisons of shift-by-constant.
-    ConstantInt *ShAmt = dyn_cast<ConstantInt>(LHSI->getOperand(1));
+    if (ConstantInt *ShAmt = dyn_cast<ConstantInt>(LHSI->getOperand(1)))
-    if (!ShAmt || !ICI.isEquality()) break;
+      if (Instruction *Res = FoldICmpShrCst(ICI, cast<BinaryOperator>(LHSI),
-
+                                            ShAmt))
-    // Check that the shift amount is in range.  If not, don't perform
+        return Res;
-    // undefined shifts.  When the shift is visited it will be
-    // simplified.
-    uint32_t TypeBits = RHSV.getBitWidth();
-    uint32_t ShAmtVal = (uint32_t)ShAmt->getLimitedValue(TypeBits);
-    if (ShAmtVal >= TypeBits)
     break;
     
-    // If we are comparing against bits always shifted out, the
-    // comparison cannot succeed.
-    APInt Comp = RHSV << ShAmtVal;
-    if (LHSI->getOpcode() == Instruction::LShr)
-      Comp = Comp.lshr(ShAmtVal);
-    else
-      Comp = Comp.ashr(ShAmtVal);
-    
-    if (Comp != RHSV) { // Comparing against a bit that we know is zero.
-      bool IsICMP_NE = ICI.getPredicate() == ICmpInst::ICMP_NE;
-      Constant *Cst = ConstantInt::get(Type::getInt1Ty(ICI.getContext()),
-                                       IsICMP_NE);
-      return ReplaceInstUsesWith(ICI, Cst);
-    }
-    
-    // Otherwise, check to see if the bits shifted out are known to be zero.
-    // If so, we can compare against the unshifted value:
-    //  (X & 4) >> 1 == 2  --> (X & 4) == 4.
-    if (LHSI->hasOneUse() && cast<BinaryOperator>(LHSI)->isExact())
-      return new ICmpInst(ICI.getPredicate(), LHSI->getOperand(0),
-                          ConstantExpr::getShl(RHS, ShAmt));
-    
-    if (LHSI->hasOneUse()) {
-      // Otherwise strength reduce the shift into an and.
-      APInt Val(APInt::getHighBitsSet(TypeBits, TypeBits - ShAmtVal));
-      Constant *Mask = ConstantInt::get(ICI.getContext(), Val);
-      
-      Value *And = Builder->CreateAnd(LHSI->getOperand(0),
-                                      Mask, LHSI->getName()+".mask");
-      return new ICmpInst(ICI.getPredicate(), And,
-                          ConstantExpr::getShl(RHS, ShAmt));
-    }
-    break;
-  }
-    
   case Instruction::SDiv:
   case Instruction::UDiv:
     // Fold: icmp pred ([us]div X, C1), C2 -> range test