[llvm] [SPIR-V] Add OpSMulExtended and OpUMulExtended builtin support (PR #187474)

[Dmitry Sidorov via llvm-commits]

================
@@ -1996,6 +1996,97 @@ static bool generateICarryBorrowInst(const SPIRV::IncomingCall *Call,
   return true;
 }
 
+// We expect a builtin in one of two forms:
+//
+//  (1) sret convention (3 arguments):
+//     void Name(ptr sret([RetType]) %result, Type %operand1, Type %operand2)
+//     =>  Res = Opcode RetType Operand1 Operand2
+//         OpStore %result Res
+//
+//  (2) direct return convention (2 arguments):
+//     RetType Name(Type %operand1, Type %operand2)
+//     =>  Res = Opcode RetType Operand1 Operand2
+//
+// RetType is a struct with two members of the same type as the operands.
+static bool generateMulExtendedInst(const SPIRV::IncomingCall *Call,
+                                    MachineIRBuilder &MIRBuilder,
+                                    SPIRVGlobalRegistry *GR) {
+  const SPIRV::DemangledBuiltin *Builtin = Call->Builtin;
+  unsigned Opcode =
+      SPIRV::lookupNativeBuiltin(Builtin->Name, Builtin->Set)->Opcode;
+  assert((Opcode == SPIRV::OpUMulExtended || Opcode == SPIRV::OpSMulExtended) &&
+         "Expected OpUMulExtended or OpSMulExtended");
+
+  const bool IsSret =
+      !Call->ReturnType || Call->ReturnType->getOpcode() == SPIRV::OpTypeVoid;
+  Register Op1Reg = IsSret ? Call->Arguments[1] : Call->Arguments[0];
+  Register Op2Reg = IsSret ? Call->Arguments[2] : Call->Arguments[1];
+
+  SPIRVTypeInst RetType;
+  if (IsSret) {
+    Register SRetReg = Call->Arguments[0];
+    SPIRVTypeInst PtrRetType = GR->getSPIRVTypeForVReg(SRetReg);
+    RetType = GR->getPointeeType(PtrRetType);
+    if (!RetType)
+      report_fatal_error("The first parameter must be a pointer");
+  } else {
+    RetType = Call->ReturnType;
+  }
+
+  if (!RetType || RetType->getOpcode() != SPIRV::OpTypeStruct)
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MrSidims wrote:

(since it's confuses me) default initialization for `SPIRVTypeInst`  is nullptr, right? 

https://github.com/llvm/llvm-project/pull/187474