[IR] SelectInst: add swapValues() utility

Summary:
Sometimes we need to swap true-val and false-val of a `SelectInst`.
Having a function for that is nicer than hand-writing it each time.

Reviewers: spatel, RKSimon, craig.topper, jdoerfert

Reviewed By: jdoerfert

Subscribers: jdoerfert, hiraditya, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D65520

llvm-svn: 367547

llvm/include/llvm/IR/Instructions.h

@@ -1764,6 +1764,10 @@ public:
   void setTrueValue(Value *V) { Op<1>() = V; }
   void setFalseValue(Value *V) { Op<2>() = V; }
 
+  /// Swap the true and false values of the select instruction.
+  /// This doesn't swap prof metadata.
+  void swapValues() { Op<1>().swap(Op<2>()); }
+
   /// Return a string if the specified operands are invalid
   /// for a select operation, otherwise return null.
   static const char *areInvalidOperands(Value *Cond, Value *True, Value *False);

llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp

@@ -1690,13 +1690,9 @@ Instruction *InstCombiner::visitSub(BinaryOperator &I) {
         if (SPF == SPF_ABS || SPF == SPF_NABS) {
           // This is a negate of an ABS/NABS pattern. Just swap the operands
           // of the select.
-          SelectInst *SI = cast<SelectInst>(Op1);
-          Value *TrueVal = SI->getTrueValue();
-          Value *FalseVal = SI->getFalseValue();
-          SI->setTrueValue(FalseVal);
-          SI->setFalseValue(TrueVal);
+          cast<SelectInst>(Op1)->swapValues();
           // Don't swap prof metadata, we didn't change the branch behavior.
-          return replaceInstUsesWith(I, SI);
+          return replaceInstUsesWith(I, Op1);
         }
       }
     }

llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp

@@ -973,8 +973,7 @@ canonicalizeMinMaxWithConstant(SelectInst &Sel, ICmpInst &Cmp,
   // If we are swapping the select operands, swap the metadata too.
   assert(Sel.getTrueValue() == RHS && Sel.getFalseValue() == LHS &&
          "Unexpected results from matchSelectPattern");
-  Sel.setTrueValue(LHS);
-  Sel.setFalseValue(RHS);
+  Sel.swapValues();
   Sel.swapProfMetadata();
   return &Sel;
 }
@@ -1056,8 +1055,7 @@ static Instruction *canonicalizeAbsNabs(SelectInst &Sel, ICmpInst &Cmp,
   }
 
   // We are swapping the select operands, so swap the metadata too.
-  Sel.setTrueValue(FVal);
-  Sel.setFalseValue(TVal);
+  Sel.swapValues();
   Sel.swapProfMetadata();
   return &Sel;
 }

llvm/lib/Transforms/Instrumentation/ControlHeightReduction.cpp

@@ -1538,10 +1538,7 @@ static bool negateICmpIfUsedByBranchOrSelectOnly(ICmpInst *ICmp,
     }
     if (auto *SI = dyn_cast<SelectInst>(U)) {
       // Swap operands
-      Value *TrueValue = SI->getTrueValue();
-      Value *FalseValue = SI->getFalseValue();
-      SI->setTrueValue(FalseValue);
-      SI->setFalseValue(TrueValue);
+      SI->swapValues();
       SI->swapProfMetadata();
       if (Scope->TrueBiasedSelects.count(SI)) {
         assert(Scope->FalseBiasedSelects.count(SI) == 0 &&