[VP] make getFunctionalOpcode return an Optional

The operation of some VP intrinsics do/will not map to regular
instruction opcodes.  Returning 'None' seems more intuitive here than
'Instruction::Call'.

Reviewed By: frasercrmck

Differential Revision: https://reviews.llvm.org/D102778

Author: Simon Moll

llvm/include/llvm/IR/IntrinsicInst.h

@@ -417,12 +417,12 @@ class VPIntrinsic : public IntrinsicInst {
   }
 
   // Equivalent non-predicated opcode
-  unsigned getFunctionalOpcode() const {
+  Optional<unsigned> getFunctionalOpcode() const {
     return GetFunctionalOpcodeForVP(getIntrinsicID());
   }
 
   // Equivalent non-predicated opcode
-  static unsigned GetFunctionalOpcodeForVP(Intrinsic::ID ID);
+  static Optional<unsigned> GetFunctionalOpcodeForVP(Intrinsic::ID ID);
 };
 
 /// This is the common base class for constrained floating point intrinsics.

llvm/lib/CodeGen/ExpandVectorPredication.cpp

@@ -217,7 +217,7 @@ CachingVPExpander::expandPredicationInBinaryOperator(IRBuilder<> &Builder,
           VPI.canIgnoreVectorLengthParam()) &&
          "Implicitly dropping %evl in non-speculatable operator!");
 
-  auto OC = static_cast<Instruction::BinaryOps>(VPI.getFunctionalOpcode());
+  auto OC = static_cast<Instruction::BinaryOps>(*VPI.getFunctionalOpcode());
   assert(Instruction::isBinaryOp(OC));
 
   Value *Op0 = VPI.getOperand(0);
@@ -316,9 +316,9 @@ Value *CachingVPExpander::expandPredication(VPIntrinsic &VPI) {
   IRBuilder<> Builder(&VPI);
 
   // Try lowering to a LLVM instruction first.
-  unsigned OC = VPI.getFunctionalOpcode();
+  auto OC = VPI.getFunctionalOpcode();
 
-  if (Instruction::isBinaryOp(OC))
+  if (OC && Instruction::isBinaryOp(*OC))
     return expandPredicationInBinaryOperator(Builder, VPI);
 
   return &VPI;

llvm/lib/IR/IntrinsicInst.cpp

@@ -317,8 +317,8 @@ bool VPIntrinsic::IsVPIntrinsic(Intrinsic::ID ID) {
 }
 
 // Equivalent non-predicated opcode
-unsigned VPIntrinsic::GetFunctionalOpcodeForVP(Intrinsic::ID ID) {
-  unsigned FunctionalOC = Instruction::Call;
+Optional<unsigned> VPIntrinsic::GetFunctionalOpcodeForVP(Intrinsic::ID ID) {
+  Optional<unsigned> FunctionalOC;
   switch (ID) {
   default:
     break;

llvm/unittests/IR/VPIntrinsicTest.cpp

@@ -183,16 +183,17 @@ TEST_F(VPIntrinsicTest, OpcodeRoundTrip) {
   unsigned FullTripCounts = 0;
   for (unsigned OC : Opcodes) {
     Intrinsic::ID VPID = VPIntrinsic::GetForOpcode(OC);
-    // no equivalent VP intrinsic available
+    // No equivalent VP intrinsic available.
     if (VPID == Intrinsic::not_intrinsic)
       continue;
 
-    unsigned RoundTripOC = VPIntrinsic::GetFunctionalOpcodeForVP(VPID);
-    // no equivalent Opcode available
-    if (RoundTripOC == Instruction::Call)
+    Optional<unsigned> RoundTripOC =
+        VPIntrinsic::GetFunctionalOpcodeForVP(VPID);
+    // No equivalent Opcode available.
+    if (!RoundTripOC)
       continue;
 
-    ASSERT_EQ(RoundTripOC, OC);
+    ASSERT_EQ(*RoundTripOC, OC);
     ++FullTripCounts;
   }
   ASSERT_NE(FullTripCounts, 0u);
@@ -207,13 +208,13 @@ TEST_F(VPIntrinsicTest, IntrinsicIDRoundTrip) {
   unsigned FullTripCounts = 0;
   for (const auto &VPDecl : *M) {
     auto VPID = VPDecl.getIntrinsicID();
-    unsigned OC = VPIntrinsic::GetFunctionalOpcodeForVP(VPID);
+    Optional<unsigned> OC = VPIntrinsic::GetFunctionalOpcodeForVP(VPID);
 
     // no equivalent Opcode available
-    if (OC == Instruction::Call)
+    if (!OC)
       continue;
 
-    Intrinsic::ID RoundTripVPID = VPIntrinsic::GetForOpcode(OC);
+    Intrinsic::ID RoundTripVPID = VPIntrinsic::GetForOpcode(*OC);
 
     ASSERT_EQ(RoundTripVPID, VPID);
     ++FullTripCounts;