JIT: Rewrite register parameter homing

src/coreclr/jit/abi.cpp

@@ -77,14 +77,14 @@ unsigned ABIPassingSegment::GetStackOffset() const
 }
 
 //-----------------------------------------------------------------------------
-// GetRegisterStoreType:
-//   Return a type that can be used to store from the register this segment is
-//   in, taking the segment's size into account.
+// GetRegisterType:
+//  Return the smallest type larger or equal to Size that most naturally
+//  represents the register this segment is passed in.
 //
 // Return Value:
-//   A type that matches ABIPassingSegment::Size and the register type.
+//   A type that matches ABIPassingSegment::Size and the register.
 //
-var_types ABIPassingSegment::GetRegisterStoreType() const
+var_types ABIPassingSegment::GetRegisterType() const
 {
     assert(IsPassedInRegister());
     if (genIsValidFloatReg(m_register))
@@ -100,6 +100,7 @@ var_types ABIPassingSegment::GetRegisterStoreType() const
                 return TYP_SIMD16;
 #endif
             default:
+                assert(!"Unexpected size for floating point register");
                 return TYP_UNDEF;
         }
     }
@@ -111,13 +112,18 @@ var_types ABIPassingSegment::GetRegisterStoreType() const
                 return TYP_UBYTE;
             case 2:
                 return TYP_USHORT;
+            case 3:
             case 4:
                 return TYP_INT;
 #ifdef TARGET_64BIT
+            case 5:
+            case 6:
+            case 7:
             case 8:
                 return TYP_LONG;
 #endif
             default:
+                assert(!"Unexpected size for integer register");
                 return TYP_UNDEF;
         }
     }

src/coreclr/jit/abi.h

@@ -31,7 +31,7 @@ class ABIPassingSegment
     // offset, relative to the first stack argument's offset.
     unsigned GetStackOffset() const;
 
-    var_types GetRegisterStoreType() const;
+    var_types GetRegisterType() const;
 
     static ABIPassingSegment InRegister(regNumber reg, unsigned offset, unsigned size);
     static ABIPassingSegment OnStack(unsigned stackOffset, unsigned offset, unsigned size);

src/coreclr/jit/codegen.h

@@ -261,13 +261,13 @@ class CodeGen final : public CodeGenInterface
     // Prolog functions and data (there are a few exceptions for more generally used things)
     //
 
-    void genEstablishFramePointer(int delta, bool reportUnwindData);
-#if defined(TARGET_LOONGARCH64) || defined(TARGET_RISCV64)
-    void genFnPrologCalleeRegArgs();
-#else
-    void genFnPrologCalleeRegArgs(regNumber xtraReg, bool* pXtraRegClobbered, RegState* regState);
-#endif
-    void genEnregisterIncomingStackArgs();
+    void      genEstablishFramePointer(int delta, bool reportUnwindData);
+    void      genHomeRegisterParams(regNumber initReg, bool* initRegStillZeroed);
+    regMaskTP genGetParameterHomingTempRegisterCandidates();
+
+    var_types genParamStackStoreType(LclVarDsc* dsc, const ABIPassingSegment& seg);
+    void      genSpillOrAddRegisterParam(unsigned lclNum, class RegGraph* graph);
+    void      genEnregisterIncomingStackArgs();
 #if defined(TARGET_ARM64) || defined(TARGET_LOONGARCH64) || defined(TARGET_RISCV64)
     void genEnregisterOSRArgsAndLocals(regNumber initReg, bool* pInitRegZeroed);
 #else