Index: llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
===================================================================
--- llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
+++ llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
@@ -1618,6 +1618,9 @@
   if (Instruction *Res = foldBinOpOfDisplacedShifts(I))
     return Res;
 
+  if (Instruction *Res = foldBinOpOfSelectAndCastOfSelectCondition(I))
+    return Res;
+
   return Changed ? &I : nullptr;
 }
 
@@ -2466,6 +2469,9 @@
     }
   }
 
+  if (Instruction *Res = foldBinOpOfSelectAndCastOfSelectCondition(I))
+    return Res;
+
   return TryToNarrowDeduceFlags();
 }
 
Index: llvm/lib/Transforms/InstCombine/InstCombineInternal.h
===================================================================
--- llvm/lib/Transforms/InstCombine/InstCombineInternal.h
+++ llvm/lib/Transforms/InstCombine/InstCombineInternal.h
@@ -454,6 +454,12 @@
   //    -> (BinOp (logic_shift (BinOp X, Y)), Mask)
   Instruction *foldBinOpShiftWithShift(BinaryOperator &I);
 
+  /// Tries to simplify binops of select and cast of the select condition.
+  ///
+  /// (Binop (cast C), (select C, T, F))
+  ///    -> (select C, C0, C1)
+  Instruction *foldBinOpOfSelectAndCastOfSelectCondition(BinaryOperator &I);
+
   /// This tries to simplify binary operations by factorizing out common terms
   /// (e. g. "(A*B)+(A*C)" -> "A*(B+C)").
   Value *tryFactorizationFolds(BinaryOperator &I);
Index: llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
===================================================================
--- llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
+++ llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
@@ -474,6 +474,9 @@
   if (Instruction *Ext = narrowMathIfNoOverflow(I))
     return Ext;
 
+  if (Instruction *Res = foldBinOpOfSelectAndCastOfSelectCondition(I))
+    return Res;
+
   // min(X, Y) * max(X, Y) => X * Y.
   if (match(&I, m_CombineOr(m_c_Mul(m_SMax(m_Value(X), m_Value(Y)),
                                     m_c_SMin(m_Deferred(X), m_Deferred(Y))),
Index: llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
===================================================================
--- llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
+++ llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
@@ -866,6 +866,74 @@
   return MatchBinOp(1);
 }
 
+// (Binop (zext C), (select C, T, F))
+//    -> (select C, (binop 1, T), (binop 0, F))
+//
+// (Binop (sext C), (select C, T, F))
+//    -> (select C, (binop -1, T), (binop 0, F))
+//
+// Attempt to simplify binary operations into a select with folded args, when
+// one operand of the binop is a select instruction and the other operand is a
+// zext/sext extension, whose value is the select condition.
+Instruction *
+InstCombinerImpl::foldBinOpOfSelectAndCastOfSelectCondition(BinaryOperator &I) {
+  // TODO: this simplification may be extended to any speculatable instruction,
+  // not just binops, and would possibly be handled better in FoldOpIntoSelect.
+  Instruction::BinaryOps Opc = I.getOpcode();
+  Value *LHS = I.getOperand(0), *RHS = I.getOperand(1);
+  Value *A, *CondVal, *TrueVal, *FalseVal;
+  Value *CastOp;
+
+  auto MatchSelectAndCast = [&](Value *CastOp, Value *SelectOp) {
+    return match(CastOp, m_ZExtOrSExt(m_Value(A))) &&
+           A->getType()->getScalarSizeInBits() == 1 &&
+           match(SelectOp, m_Select(m_Value(CondVal), m_Value(TrueVal),
+                                    m_Value(FalseVal)));
+  };
+
+  // Make sure one side of the binop is a select instruction, and the other is a
+  // zero/sign extension operating on a i1.
+  if (MatchSelectAndCast(LHS, RHS))
+    CastOp = LHS;
+  else if (MatchSelectAndCast(RHS, LHS))
+    CastOp = RHS;
+  else
+    return nullptr;
+
+  auto NewFoldedConst = [&](bool IsTrueArm, Value *V) {
+    bool IsCastOpRHS = (CastOp == RHS);
+    bool IsZExt = isa<ZExtInst>(CastOp);
+    Constant *C;
+
+    if (IsTrueArm) {
+      C = Constant::getNullValue(V->getType());
+    } else if (IsZExt) {
+      C = Constant::getIntegerValue(
+          V->getType(), APInt(V->getType()->getIntegerBitWidth(), 1));
+    } else {
+      C = Constant::getAllOnesValue(V->getType());
+    }
+
+    return IsCastOpRHS ? Builder.CreateBinOp(Opc, V, C)
+                       : Builder.CreateBinOp(Opc, C, V);
+  };
+
+  // If the value used in the zext/sext is the select condition, and the true
+  // argument is a constant, the binop can be simplified.
+  if (CondVal == A)
+    return SelectInst::Create(CondVal, NewFoldedConst(false, TrueVal),
+                              NewFoldedConst(true, FalseVal));
+
+  // If the value used in the zext/sext is the negated of the select
+  // condition, and the false argument is a constant, the binop can be
+  // simplified.
+  if (match(A, m_Not(m_Specific(CondVal))))
+    return SelectInst::Create(CondVal, NewFoldedConst(true, TrueVal),
+                              NewFoldedConst(false, FalseVal));
+
+  return nullptr;
+}
+
 Value *InstCombinerImpl::tryFactorizationFolds(BinaryOperator &I) {
   Value *LHS = I.getOperand(0), *RHS = I.getOperand(1);
   BinaryOperator *Op0 = dyn_cast<BinaryOperator>(LHS);