[NFC][InstCombine] Make use of unknown profile info clear in the API name (#162766)

Making the choice more clear from the API name, otherwise it'd be very easy for one to just "not bother" with the `MDFrom`​, especially since it is optional and follows the optional `Name`​ - but this time we'd have a harder time detecting it's effectivelly dropped metadata.

Author: mtrofin

llvm/include/llvm/IR/Instructions.h

@@ -1715,7 +1715,7 @@ class SelectInst : public Instruction {
   static SelectInst *Create(Value *C, Value *S1, Value *S2,
                             const Twine &NameStr = "",
                             InsertPosition InsertBefore = nullptr,
-                            Instruction *MDFrom = nullptr) {
+                            const Instruction *MDFrom = nullptr) {
     SelectInst *Sel =
         new (AllocMarker) SelectInst(C, S1, S2, NameStr, InsertBefore);
     if (MDFrom)

llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp

@@ -880,11 +880,13 @@ Instruction *InstCombinerImpl::foldAddWithConstant(BinaryOperator &Add) {
   // zext(bool) + C -> bool ? C + 1 : C
   if (match(Op0, m_ZExt(m_Value(X))) &&
       X->getType()->getScalarSizeInBits() == 1)
-    return createSelectInst(X, InstCombiner::AddOne(Op1C), Op1);
+    return createSelectInstWithUnknownProfile(X, InstCombiner::AddOne(Op1C),
+                                              Op1);
   // sext(bool) + C -> bool ? C - 1 : C
   if (match(Op0, m_SExt(m_Value(X))) &&
       X->getType()->getScalarSizeInBits() == 1)
-    return createSelectInst(X, InstCombiner::SubOne(Op1C), Op1);
+    return createSelectInstWithUnknownProfile(X, InstCombiner::SubOne(Op1C),
+                                              Op1);
 
   // ~X + C --> (C-1) - X
   if (match(Op0, m_Not(m_Value(X)))) {

llvm/lib/Transforms/InstCombine/InstCombineInternal.h

@@ -471,15 +471,16 @@ class LLVM_LIBRARY_VISIBILITY InstCombinerImpl final
   Value *simplifyNonNullOperand(Value *V, bool HasDereferenceable,
                                 unsigned Depth = 0);
 
-  SelectInst *createSelectInst(Value *C, Value *S1, Value *S2,
-                               const Twine &NameStr = "",
-                               InsertPosition InsertBefore = nullptr,
-                               Instruction *MDFrom = nullptr) {
-    SelectInst *SI =
-        SelectInst::Create(C, S1, S2, NameStr, InsertBefore, MDFrom);
-    if (!MDFrom)
-      setExplicitlyUnknownBranchWeightsIfProfiled(*SI, F, DEBUG_TYPE);
-    return SI;
+  /// Create `select C, S1, S2`. Use only when the profile cannot be calculated
+  /// from existing profile metadata: if the Function has profiles, this will
+  /// set the profile of this select to "unknown".
+  SelectInst *
+  createSelectInstWithUnknownProfile(Value *C, Value *S1, Value *S2,
+                                     const Twine &NameStr = "",
+                                     InsertPosition InsertBefore = nullptr) {
+    auto *Sel = SelectInst::Create(C, S1, S2, NameStr, InsertBefore, nullptr);
+    setExplicitlyUnknownBranchWeightsIfProfiled(*Sel, F, DEBUG_TYPE);
+    return Sel;
   }
 
 public:

llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp

@@ -1253,7 +1253,8 @@ Instruction *InstCombinerImpl::visitShl(BinaryOperator &I) {
     // shl (zext i1 X), C1 --> select (X, 1 << C1, 0)
     if (match(Op0, m_ZExt(m_Value(X))) && X->getType()->isIntOrIntVectorTy(1)) {
       auto *NewC = Builder.CreateShl(ConstantInt::get(Ty, 1), C1);
-      return createSelectInst(X, NewC, ConstantInt::getNullValue(Ty));
+      return createSelectInstWithUnknownProfile(X, NewC,
+                                                ConstantInt::getNullValue(Ty));
     }
   }
 

llvm/lib/Transforms/InstCombine/InstructionCombining.cpp

@@ -1737,7 +1737,7 @@ Instruction *InstCombinerImpl::foldBinopOfSextBoolToSelect(BinaryOperator &BO) {
   Constant *Zero = ConstantInt::getNullValue(BO.getType());
   Value *TVal = Builder.CreateBinOp(BO.getOpcode(), Ones, C);
   Value *FVal = Builder.CreateBinOp(BO.getOpcode(), Zero, C);
-  return createSelectInst(X, TVal, FVal);
+  return createSelectInstWithUnknownProfile(X, TVal, FVal);
 }
 
 static Value *simplifyOperationIntoSelectOperand(Instruction &I, SelectInst *SI,