InstSimplify: Optimize away pointless comparisons

[oota-llvm.git] / lib / Analysis / InstructionSimplify.cpp

diff --git a/lib/Analysis/InstructionSimplify.cpp b/lib/Analysis/InstructionSimplify.cpp
index 2cf1661cfd90ac57b84b3479f59f090499625dc9..b7882651d36f7362df330baa143249deaf3522a4 100644 (file)
--- a/lib/Analysis/InstructionSimplify.cpp
+++ b/lib/Analysis/InstructionSimplify.cpp
@@ -1011,6 +1011,10 @@ static Value *SimplifyDiv(Instruction::BinaryOps Opcode, Value *Op0, Value *Op1,
   if (match(Op1, m_Undef()))
     return Op1;
 
+  // X / 0 -> undef, we don't need to preserve faults!
+  if (match(Op1, m_Zero()))
+    return UndefValue::get(Op1->getType());
+
   // undef / X -> 0
   if (match(Op0, m_Undef()))
     return Constant::getNullValue(Op0->getType());
@@ -1334,6 +1338,11 @@ static Value *SimplifyRightShift(unsigned Opcode, Value *Op0, Value *Op1,
   if (Op0 == Op1)
     return Constant::getNullValue(Op0->getType());
 
+  // undef >> X -> 0
+  // undef >> X -> undef (if it's exact)
+  if (match(Op0, m_Undef()))
+    return isExact ? Op0 : Constant::getNullValue(Op0->getType());
+
   // The low bit cannot be shifted out of an exact shift if it is set.
   if (isExact) {
     unsigned BitWidth = Op0->getType()->getScalarSizeInBits();
@@ -1356,8 +1365,9 @@ static Value *SimplifyShlInst(Value *Op0, Value *Op1, bool isNSW, bool isNUW,
     return V;
 
   // undef << X -> 0
+  // undef << X -> undef if (if it's NSW/NUW)
   if (match(Op0, m_Undef()))
-    return Constant::getNullValue(Op0->getType());
+    return isNSW || isNUW ? Op0 : Constant::getNullValue(Op0->getType());
 
   // (X >> A) << A -> X
   Value *X;
@@ -1382,10 +1392,6 @@ static Value *SimplifyLShrInst(Value *Op0, Value *Op1, bool isExact,
                                     MaxRecurse))
       return V;
 
-  // undef >>l X -> 0
-  if (match(Op0, m_Undef()))
-    return Constant::getNullValue(Op0->getType());
-
   // (X << A) >> A -> X
   Value *X;
   if (match(Op0, m_NUWShl(m_Value(X), m_Specific(Op1))))
@@ -1416,10 +1422,6 @@ static Value *SimplifyAShrInst(Value *Op0, Value *Op1, bool isExact,
   if (match(Op0, m_AllOnes()))
     return Op0;
 
-  // undef >>a X -> all ones
-  if (match(Op0, m_Undef()))
-    return Constant::getAllOnesValue(Op0->getType());
-
   // (X << A) >> A -> X
   Value *X;
   if (match(Op0, m_NSWShl(m_Value(X), m_Specific(Op1))))
@@ -3153,10 +3155,10 @@ static Value *SimplifySelectInst(Value *CondVal, Value *TrueVal,
   if (const auto *ICI = dyn_cast<ICmpInst>(CondVal)) {
     Value *X;
     const APInt *Y;
-    if (ICI->isEquality() &&
+    ICmpInst::Predicate Pred = ICI->getPredicate();
+    if (ICmpInst::isEquality(Pred) &&
         match(ICI->getOperand(0), m_And(m_Value(X), m_APInt(Y))) &&
         match(ICI->getOperand(1), m_Zero())) {
-      ICmpInst::Predicate Pred = ICI->getPredicate();
       const APInt *C;
       // (X & Y) == 0 ? X & ~Y : X  --> X
       // (X & Y) != 0 ? X & ~Y : X  --> X & ~Y
@@ -3182,6 +3184,42 @@ static Value *SimplifySelectInst(Value *CondVal, Value *TrueVal,
           return Pred == ICmpInst::ICMP_EQ ? TrueVal : FalseVal;
       }
     }
+    if (Pred == ICmpInst::ICMP_SLT && match(ICI->getOperand(1), m_Zero())) {
+      // (X < 0) ? X : X | SignBit  --> X | SignBit
+      if (TrueVal == ICI->getOperand(0) &&
+          match(FalseVal, m_Or(m_Specific(TrueVal), m_SignBit())))
+        return FalseVal;
+      // (X < 0) ? X | SignBit : X  --> X
+      if (FalseVal == ICI->getOperand(0) &&
+          match(TrueVal, m_Or(m_Specific(FalseVal), m_SignBit())))
+        return FalseVal;
+      // (X < 0) ? X & INT_MAX : X  --> X & INT_MAX
+      if (FalseVal == ICI->getOperand(0) &&
+          match(TrueVal, m_And(m_Specific(FalseVal), m_MaxSignedValue())))
+        return TrueVal;
+      // (X < 0) ? X : X & INT_MAX  --> X
+      if (TrueVal == ICI->getOperand(0) &&
+          match(FalseVal, m_And(m_Specific(TrueVal), m_MaxSignedValue())))
+        return TrueVal;
+    }
+    if (Pred == ICmpInst::ICMP_SGT && match(ICI->getOperand(1), m_AllOnes())) {
+      // (X > -1) ? X : X | SignBit  --> X
+      if (TrueVal == ICI->getOperand(0) &&
+          match(FalseVal, m_Or(m_Specific(TrueVal), m_SignBit())))
+        return TrueVal;
+      // (X > -1) ? X | SignBit : X  --> X | SignBit
+      if (FalseVal == ICI->getOperand(0) &&
+          match(TrueVal, m_Or(m_Specific(FalseVal), m_SignBit())))
+        return TrueVal;
+      // (X > -1) ? X & INT_MAX : X  --> X
+      if (FalseVal == ICI->getOperand(0) &&
+          match(TrueVal, m_And(m_Specific(FalseVal), m_MaxSignedValue())))
+        return FalseVal;
+      // (X > -1) ? X : X & INT_MAX  --> X & INT_MAX
+      if (TrueVal == ICI->getOperand(0) &&
+          match(FalseVal, m_And(m_Specific(TrueVal), m_MaxSignedValue())))
+        return FalseVal;
+    }
   }
 
   return nullptr;