[InstCombine] Ensure all undef operands are handled before binary ins…

…truction constant folding

As noted in PR18355, this patch makes it clear that all cases with undef operands have been handled before further constant folding is attempted.

Differential Revision: http://reviews.llvm.org/D18305

llvm-svn: 263994

llvm/lib/IR/ConstantFold.cpp

@@ -916,9 +916,11 @@ Constant *llvm::ConstantFoldInsertValueInstruction(Constant *Agg,
 
 Constant *llvm::ConstantFoldBinaryInstruction(unsigned Opcode,
                                               Constant *C1, Constant *C2) {
+  assert(Instruction::isBinaryOp(Opcode) && "Non-binary instruction detected");
+
   // Handle UndefValue up front.
   if (isa<UndefValue>(C1) || isa<UndefValue>(C2)) {
-    switch (Opcode) {
+    switch (static_cast<Instruction::BinaryOps>(Opcode)) {
     case Instruction::Xor:
       if (isa<UndefValue>(C1) && isa<UndefValue>(C2))
         // Handle undef ^ undef -> 0 special case. This is a common
@@ -998,9 +1000,22 @@ Constant *llvm::ConstantFoldBinaryInstruction(unsigned Opcode,
         return C1;
       // undef << X -> 0
       return Constant::getNullValue(C1->getType());
+    case Instruction::FAdd:
+    case Instruction::FSub:
+    case Instruction::FMul:
+    case Instruction::FDiv:
+    case Instruction::FRem:
+      // TODO: UNDEF handling for binary float instructions.
+      return nullptr;
+    case Instruction::BinaryOpsEnd:
+      llvm_unreachable("Invalid BinaryOp");
     }
   }
 
+  // At this point neither constant should be an UndefValue.
+  assert(!isa<UndefValue>(C1) && !isa<UndefValue>(C2) &&
+         "Unexpected UndefValue");
+
   // Handle simplifications when the RHS is a constant int.
   if (ConstantInt *CI2 = dyn_cast<ConstantInt>(C2)) {
     switch (Opcode) {
@@ -1102,7 +1117,6 @@ Constant *llvm::ConstantFoldBinaryInstruction(unsigned Opcode,
       return ConstantExpr::get(Opcode, C2, C1);
   }
 
-  // At this point we know neither constant is an UndefValue.
   if (ConstantInt *CI1 = dyn_cast<ConstantInt>(C1)) {
     if (ConstantInt *CI2 = dyn_cast<ConstantInt>(C2)) {
       const APInt &C1V = CI1->getValue();