[InstCombine] Support folding of add instructions with vector constants into select operations

[craig.topper]

Summary

We currently only fold scalar add of constants into selects. This improves this to support vectors too.

[spatel]

LGTM.
(I stopped getting emails from Phab about 4 days ago; not sure if this is affecting everyone.)

lib/Transforms/InstCombine/InstCombineAddSub.cpp

if (match(LHS, m_Xor(m_Value(XorLHS), m_ConstantInt(XorRHS)))) {
       // (X + signbit) + C could have gotten canonicalized to (X ^ signbit) + C,
       // transform them into (X + (signbit ^ C))
       if (XorRHS->getValue().isSignBit())
         return BinaryOperator::CreateAdd(XorLHS,
                                          ConstantExpr::getXor(XorRHS, CI));
     }
   }
 
-  if (isa<Constant>(RHS) && isa<PHINode>(LHS))
-    if (Instruction *NV = FoldOpIntoPhi(I))
+  if (isa<Constant>(RHS))
+    if (Instruction *NV = foldOpWithConstantIntoOperand(I))
       return NV;
 
   if (I.getType()->getScalarType()->isIntegerTy(1))
     return BinaryOperator::CreateXor(LHS, RHS);
 
   // X + X --> X << 1
   if (LHS == RHS) {
     BinaryOperator *New =
if (LHS->hasOneUse() &&
       APInt AddRHSHighBitsAnd(AddRHSHighBits & C2->getValue());
 
       if (AddRHSHighBits == AddRHSHighBitsAnd) {
         // Okay, the xform is safe.  Insert the new add pronto.
         Value *NewAdd = Builder->CreateAdd(X, CRHS, LHS->getName());
         return BinaryOperator::CreateAnd(NewAdd, C2);
       }
     }
-
-    // Try to fold constant add into select arguments.
-    if (SelectInst *SI = dyn_cast<SelectInst>(LHS))
-      if (Instruction *R = FoldOpIntoSelect(I, SI))
-        return R;
   }
 
   // add (select X 0 (sub n A)) A  -->  select X A n
   {
     SelectInst *SI = dyn_cast<SelectInst>(LHS);
     Value *A = RHS;
     if (!SI) {
       SI = dyn_cast<SelectInst>(RHS);

test/Transforms/InstCombine/add.ll

 ;
   %A = select i1 %C, i32 1000, i32 10
   %V = add i32 123, %A
   ret i32 %V
 }
 
 define <2 x i32> @test42vec(i1 %C) {
 ; CHECK-LABEL: @test42vec(
-; CHECK-NEXT:    [[A:%.*]] = select i1 [[C:%.*]], <2 x i32> <i32 1000, i32 1000>, <2 x i32> <i32 10, i32 10>
-; CHECK-NEXT:    [[V:%.*]] = add nuw nsw <2 x i32> [[A]], <i32 123, i32 123>
+; CHECK-NEXT:    [[V:%.*]] = select i1 [[C:%.*]], <2 x i32> <i32 1123, i32 1123>, <2 x i32> <i32 133, i32 133>
 ; CHECK-NEXT:    ret <2 x i32> [[V]]
 ;
   %A = select i1 %C, <2 x i32> <i32 1000, i32 1000>, <2 x i32> <i32 10, i32 10>
   %V = add <2 x i32> <i32 123, i32 123>, %A
   ret <2 x i32> %V
 }
 
 define <2 x i32> @test42vec2(i1 %C) {
 ; CHECK-LABEL: @test42vec2(
-; CHECK-NEXT:    [[A:%.*]] = select i1 [[C:%.*]], <2 x i32> <i32 1000, i32 2500>, <2 x i32> <i32 10, i32 30>
-; CHECK-NEXT:    [[V:%.*]] = add nuw nsw <2 x i32> [[A]], <i32 123, i32 333>
+; CHECK-NEXT:    [[V:%.*]] = select i1 [[C:%.*]], <2 x i32> <i32 1123, i32 2833>, <2 x i32> <i32 133, i32 363>
 ; CHECK-NEXT:    ret <2 x i32> [[V]]
 ;
   %A = select i1 %C, <2 x i32> <i32 1000, i32 2500>, <2 x i32> <i32 10, i32 30>
   %V = add <2 x i32> <i32 123, i32 333>, %A
   ret <2 x i32> %V
 }
 
 define i32 @test55(i1 %which) {