Enable implicit fallthrough warning

eng/native/configurecompiler.cmake

@@ -324,6 +324,11 @@ if (CLR_CMAKE_HOST_UNIX)
   add_compile_options(-Wno-unused-function)
   add_compile_options(-Wno-tautological-compare)
 
+  check_cxx_compiler_flag(-Wimplicit-fallthrough COMPILER_SUPPORTS_W_IMPLICIT_FALLTHROUGH)
+  if (COMPILER_SUPPORTS_W_IMPLICIT_FALLTHROUGH)
+    add_compile_options(-Wimplicit-fallthrough)
+  endif()
+
   #These seem to indicate real issues
   add_compile_options($<$<COMPILE_LANGUAGE:CXX>:-Wno-invalid-offsetof>)
 

src/coreclr/src/ToolBox/superpmi/mcs/verbildump.cpp

@@ -893,6 +893,7 @@ void DumpILToConsoleBare(unsigned char* ilCode, int len)
                         LogError("unknown ilCode 0xfe%2x at offset %d in MethodGen::PrettyPrint", ilCode[i], i);
                         break;
                 }
+                break;
             default:
                 LogError("unknown ilCode 0x%02x at offset %d in MethodGen::PrettyPrint", ilCode[i], i);
                 break;

src/coreclr/src/classlibnative/bcltype/varargsnative.cpp

@@ -575,7 +575,8 @@ VarArgsNative::GetNextArgHelper(
             }
 #endif
 
-        // fall through
+            FALLTHROUGH;
+
         case ELEMENT_TYPE_CLASS: {
             value->type = data->SigPtr.GetTypeHandleThrowing(data->ArgCookie->pModule, &typeContext);
 

src/coreclr/src/debug/di/rstype.cpp

@@ -590,7 +590,7 @@ HRESULT CordbType::MkType(CordbAppDomain * pAppDomain,
 
       pClass->SetIsValueClass(true);
       pClass->SetIsValueClassKnown(true);
-      // drop through
+      FALLTHROUGH;
 
     case ELEMENT_TYPE_CLASS:
         {
@@ -2009,6 +2009,7 @@ void CordbType::TypeToExpandedTypeData(DebuggerIPCE_ExpandedTypeData *data)
         }
     case ELEMENT_TYPE_END:
         _ASSERTE(!"bad element type!");
+        break;
 
     default:
         data->elementType = m_elementType;
@@ -2389,6 +2390,7 @@ HRESULT CordbType::GetTypeID(COR_TYPEID *pId)
         case ELEMENT_TYPE_BYREF:
         case ELEMENT_TYPE_FNPTR:
             IfFailThrow(CORDBG_E_UNSUPPORTED);
+            break;
         default:
             _ASSERTE(!"unexpected element type!");
             IfFailThrow(CORDBG_E_UNSUPPORTED);

src/coreclr/src/debug/ee/amd64/amd64walker.cpp

@@ -580,6 +580,7 @@ static int opSize(Amd64InstrDecode::InstrForm form, int pp, bool W, bool L, bool
     // P_M6B_or_M4B
     case Amd64InstrDecode::InstrForm::MOnly_P_M6B_or_M4B:
         opSize = P ? 6 : 4;
+        break;
     // M4B
     case Amd64InstrDecode::InstrForm::M1st_M4B:
     case Amd64InstrDecode::InstrForm::M1st_M4B_I1B:
@@ -833,7 +834,7 @@ void NativeWalker::DecodeInstructionForPatchSkip(const BYTE *address, Instructio
                 opCodeMap = Primary;
                 break;
             }
-            // Fall through
+            FALLTHROUGH;
         case 0xc4: // Vex 3-byte
             opCodeMap = (OpcodeMap)(int(address[0]) << 8 | (address[1] & 0x1f));
             // W is the top bit of opcode2.
@@ -965,7 +966,7 @@ void NativeWalker::DecodeInstructionForPatchSkip(const BYTE *address, Instructio
                     case 2:
                     case 3:
                         pInstrAttrib->m_fIsCall = true;
-                        // fall through
+                        FALLTHROUGH;
                     case 4:
                     case 5:
                         pInstrAttrib->m_fIsAbsBranch = true;

src/coreclr/src/debug/ee/controller.cpp

@@ -5883,7 +5883,7 @@ bool DebuggerStepper::TrapStep(ControllerStackInfo *info, bool in)
                 // the case we want to use...
                 fIsJump = true;
 
-                // fall through...
+                FALLTHROUGH;
 
             case WALK_CALL:
                 LOG((LF_CORDB,LL_INFO10000, "DC::TS:Imm:WALK_CALL ip=%p nextip=%p skipip=%p\n", walker.GetIP(), walker.GetNextIP(), walker.GetSkipIP()));

src/coreclr/src/debug/ee/debugger.cpp

@@ -10722,6 +10722,7 @@ bool Debugger::HandleIPCEvent(DebuggerIPCEvent * pEvent)
         //
         // For regular (non-jit) attach, fall through to do an async break.
         //
+        FALLTHROUGH;
 
     case DB_IPCE_ASYNC_BREAK:
         {
@@ -12138,7 +12139,7 @@ void Debugger::TypeHandleToExpandedTypeInfo(AreValueTypesBoxed boxed,
     case ELEMENT_TYPE_VALUETYPE:
         if (boxed == OnlyPrimitivesUnboxed || boxed == AllBoxed)
             res->elementType = ELEMENT_TYPE_CLASS;
-        // drop through
+        FALLTHROUGH;
 
     case ELEMENT_TYPE_CLASS:
         {

src/coreclr/src/gc/unix/gcenv.unix.cpp

@@ -28,6 +28,12 @@
 #undef min
 #undef max
 
+#if __has_cpp_attribute(fallthrough)
+#define FALLTHROUGH [[fallthrough]]
+#else
+#define FALLTHROUGH
+#endif
+
 #include <algorithm>
 
 #if HAVE_SYS_TIME_H
@@ -792,8 +798,10 @@ bool ReadMemoryValueFromFile(const char* filename, uint64_t* val)
     {
     case 'g':
     case 'G': multiplier = 1024;
+              FALLTHROUGH;
     case 'm':
     case 'M': multiplier = multiplier * 1024;
+              FALLTHROUGH;
     case 'k':
     case 'K': multiplier = multiplier * 1024;
     }

src/coreclr/src/ilasm/assem.cpp

@@ -1611,16 +1611,26 @@ unsigned hash(
    switch(len)              /* all the case statements fall through */
    {
        case 11: c+=((unsigned)k[10] << 24);
+                FALLTHROUGH;
        case 10: c+=((unsigned)k[9] << 16);
+                FALLTHROUGH;
        case 9 : c+=((unsigned)k[8] << 8);
+                FALLTHROUGH;
           /* the first byte of c is reserved for the length */
        case 8 : b+=((unsigned)k[7] << 24);
+                FALLTHROUGH;
        case 7 : b+=((unsigned)k[6] << 16);
+                FALLTHROUGH;
        case 6 : b+=((unsigned)k[5] << 8);
+                FALLTHROUGH;
        case 5 : b+=k[4];
+                FALLTHROUGH;
        case 4 : a+=((unsigned)k[3] << 24);
+                FALLTHROUGH;
        case 3 : a+=((unsigned)k[2] << 16);
+                FALLTHROUGH;
        case 2 : a+=((unsigned)k[1] << 8);
+                FALLTHROUGH;
        case 1 : a+=k[0];
      /* case 0: nothing left to add */
    }

src/coreclr/src/ilasm/assembler.cpp

@@ -1578,6 +1578,7 @@ void Assembler::EmitInstrVarByName(Instr* instr, __in __nullterminated char* lab
         case CEE_STARG:
         case CEE_STARG_S:
             nArgVarFlag++;
+            FALLTHROUGH;
         case CEE_LDLOCA:
         case CEE_LDLOCA_S:
         case CEE_LDLOC:

src/coreclr/src/ilasm/prebuilt/asmparse.cpp

@@ -2019,6 +2019,7 @@ YYLOCAL YYNEAR YYPASCAL YYPARSER()
 
 		yyerrlab:
 			++yynerrs;
+			FALLTHROUGH;
 
 		case 1:
 		case 2: /* incompletely recovered error ... try again */

src/coreclr/src/ildasm/dasm.cpp

@@ -2008,6 +2008,7 @@ BYTE* PrettyPrintCABlobValue(PCCOR_SIGNATURE &typePtr,
                 break;
             case ELEMENT_TYPE_CLASS        :
                 typePtr += CorSigUncompressToken(typePtr, &tk); //skip the following token
+                FALLTHROUGH;
             case SERIALIZATION_TYPE_TYPE   :
                 appendStr(out,KEYWORD("type"));
                 appendStr(out,appendix);
@@ -2668,6 +2669,7 @@ void DumpDefaultValue(mdToken tok, __inout __nullterminated char* szString, void
                 break;
             }
             //else fall thru to default case, to report the error
+            FALLTHROUGH;
 
         default:
             szptr+=sprintf_s(szptr,SZSTRING_REMAINING_SIZE(szptr),ERRORMSG(" /* ILLEGAL CONSTANT type:0x%02X, size:%d bytes, blob: "),MDDV.m_bType,MDDV.m_cbSize);

src/coreclr/src/ildasm/dasm_sz.cpp

@@ -211,6 +211,7 @@ unsigned SizeOfField(PCCOR_SIGNATURE *ppSig, ULONG cSig, IMDInternalImport* pImp
                     case ELEMENT_TYPE_CMOD_OPT  :
                     case ELEMENT_TYPE_CMOD_REQD :
                         *ppSig += CorSigUncompressToken(*ppSig, &tk);
+                        FALLTHROUGH;
                     case ELEMENT_TYPE_PINNED    :
                     case ELEMENT_TYPE_SZARRAY    : // uElementNumber doesn't change
                         if(*ppSig < pSigEnd) Reiterate = TRUE;

src/coreclr/src/inc/palclr_win.h

@@ -140,4 +140,8 @@
 typedef HMODULE NATIVE_LIBRARY_HANDLE;
 #endif // HOST_WINDOWS
 
+#ifndef FALLTHROUGH
+#define FALLTHROUGH __fallthrough
+#endif // FALLTHROUGH
+
 #endif	// __PALCLR_WIN_H__

src/coreclr/src/jit/assertionprop.cpp

@@ -4546,7 +4546,7 @@ void Compiler::optImpliedByCopyAssertion(AssertionDsc* copyAssertion, AssertionD
                 // This is the ngen case where we have an indirection of an address.
                 noway_assert((impAssertion->op1.kind == O1K_EXACT_TYPE) || (impAssertion->op1.kind == O1K_SUBTYPE));
 
-                __fallthrough;
+                FALLTHROUGH;
 
             case O2K_CONST_INT:
                 usable = op1MatchesCopy && (impAssertion->op2.u1.iconVal == depAssertion->op2.u1.iconVal);

src/coreclr/src/jit/codegenarmarch.cpp

@@ -207,7 +207,7 @@ void CodeGen::genCodeForTreeNode(GenTree* treeNode)
         case GT_AND:
             assert(varTypeIsIntegralOrI(treeNode));
 
-            __fallthrough;
+            FALLTHROUGH;
 
 #if !defined(TARGET_64BIT)
         case GT_ADD_LO:

src/coreclr/src/jit/codegencommon.cpp

@@ -1421,7 +1421,7 @@ bool CodeGen::genCreateAddrMode(GenTree*  addr,
                         return false; // Need overflow check
                     }
 
-                    __fallthrough;
+                    FALLTHROUGH;
 
                 case GT_LSH:
 
@@ -1486,7 +1486,7 @@ bool CodeGen::genCreateAddrMode(GenTree*  addr,
                 break;
             }
 
-            __fallthrough;
+            FALLTHROUGH;
 
         case GT_LSH:
 
@@ -1568,7 +1568,7 @@ bool CodeGen::genCreateAddrMode(GenTree*  addr,
                 break;
             }
 
-            __fallthrough;
+            FALLTHROUGH;
 
         case GT_LSH:
 
@@ -8401,7 +8401,7 @@ void CodeGen::genFnEpilog(BasicBlock* block)
 
                     // otherwise the target address doesn't fit in an immediate
                     // so we have to burn a register...
-                    __fallthrough;
+                    FALLTHROUGH;
 
                 case IAT_PVALUE:
                     // Load the address into a register, load indirect and call  through a register

src/coreclr/src/jit/codegenlinear.cpp

@@ -720,7 +720,7 @@ void CodeGen::genCodeForBBlist()
 
             case BBJ_EHCATCHRET:
                 genEHCatchRet(block);
-                __fallthrough;
+                FALLTHROUGH;
 
             case BBJ_EHFINALLYRET:
             case BBJ_EHFILTERRET:
@@ -731,6 +731,7 @@ void CodeGen::genCodeForBBlist()
 
             case BBJ_EHCATCHRET:
                 noway_assert(!"Unexpected BBJ_EHCATCHRET"); // not used on x86
+                break;
 
             case BBJ_EHFINALLYRET:
             case BBJ_EHFILTERRET:

src/coreclr/src/jit/codegenxarch.cpp

@@ -1481,7 +1481,7 @@ void CodeGen::genCodeForTreeNode(GenTree* treeNode)
 #ifdef TARGET_X86
             assert(!treeNode->IsIconHandle(GTF_ICON_TLS_HDL));
 #endif // TARGET_X86
-            __fallthrough;
+            FALLTHROUGH;
 
         case GT_CNS_DBL:
             genSetRegToConst(targetReg, targetType, treeNode);
@@ -1504,7 +1504,7 @@ void CodeGen::genCodeForTreeNode(GenTree* treeNode)
                 genCodeForBinary(treeNode->AsOp());
                 break;
             }
-            __fallthrough;
+            FALLTHROUGH;
         case GT_MOD:
         case GT_UMOD:
         case GT_UDIV:
@@ -1516,7 +1516,7 @@ void CodeGen::genCodeForTreeNode(GenTree* treeNode)
         case GT_AND:
             assert(varTypeIsIntegralOrI(treeNode));
 
-            __fallthrough;
+            FALLTHROUGH;
 
 #if !defined(TARGET_64BIT)
         case GT_ADD_LO:

src/coreclr/src/jit/compiler.cpp

@@ -8747,7 +8747,7 @@ void cTreeFlags(Compiler* comp, GenTree* tree)
                 {
                     chars += printf("[INX_STRING_LAYOUT]");
                 }
-                __fallthrough;
+                FALLTHROUGH;
             case GT_INDEX_ADDR:
                 if (tree->gtFlags & GTF_INX_RNGCHK)
                 {
@@ -8965,7 +8965,7 @@ void cTreeFlags(Compiler* comp, GenTree* tree)
                 {
                     chars += printf("[BLK_HASGCPTR]");
                 }
-                __fallthrough;
+                FALLTHROUGH;
 
             case GT_BLK:
             case GT_DYN_BLK:

src/coreclr/src/jit/compiler.h

@@ -10348,7 +10348,7 @@ class GenTreeVisitor
                         return result;
                     }
                 }
-                __fallthrough;
+                FALLTHROUGH;
 
             // Leaf nodes
             case GT_CATCH_ARG:
@@ -10393,7 +10393,7 @@ class GenTreeVisitor
                         return result;
                     }
                 }
-                __fallthrough;
+                FALLTHROUGH;
 
             // Standard unary operators
             case GT_NOT:

src/coreclr/src/jit/compiler.hpp

@@ -4347,7 +4347,7 @@ void GenTree::VisitOperands(TVisitor visitor)
             {
                 return;
             }
-            __fallthrough;
+            FALLTHROUGH;
 
         // Standard unary operators
         case GT_STORE_LCL_VAR:

src/coreclr/src/jit/disasm.cpp

@@ -964,7 +964,7 @@ size_t DisAssembler::CbDisassemble(DIS*        pdis,
                 }
             }
 
-                __fallthrough;
+                FALLTHROUGH;
 
             case DISX86::trmtaJmpShort:
             case DISX86::trmtaJmpNear:
@@ -1022,7 +1022,7 @@ size_t DisAssembler::CbDisassemble(DIS*        pdis,
                 }
             }
 
-                __fallthrough;
+                FALLTHROUGH;
 
             case DISARM64::TRMTA::trmtaBra:
             case DISARM64::TRMTA::trmtaBraCase:

src/coreclr/src/jit/eeinterface.cpp

@@ -142,7 +142,7 @@ const char* Compiler::eeGetMethodFullName(CORINFO_METHOD_HANDLE hnd)
                         }
                     }
                 }
-                    __fallthrough;
+                    FALLTHROUGH;
                 default:
                     pParam->pArgNames[i] = varTypeName(type);
                     break;
@@ -177,7 +177,7 @@ const char* Compiler::eeGetMethodFullName(CORINFO_METHOD_HANDLE hnd)
                         }
                     }
                 }
-                    __fallthrough;
+                    FALLTHROUGH;
                 default:
                     pParam->returnType = varTypeName(retType);
                     break;