v4.6.0-mcs251-20260804

SDCC MCS-251 (C251) Port — v4.6.0-mcs251, built 2026-08-04

• New MCS-251 target (Intel/STC 8-bit MCU with 24-bit address space)

• STC32G144K246 SoC support with QEMU emulation

• MCS251 ISA: byte extensions, MOVH, native word/dword arithmetic

• Standalone MCS251 code generation backend (gen.c / gen_lower.c.inc)

• Fixed register allocation for R0-R15 byte/word/dword tuples

• MCS251-specific register tracking and peephole optimization

• Native MCS251 multiplication (MUL) and dword add/sub

• DPTR value tracking cache for redundant reload elimination

• WR stack-operand merge (10→4 bytes per access)

• ELF32 executable output from the MCS-251 linker

• Native big-endian MCS251 ABI with 32-bit size_t

• Big-endian register tuples and stack frames

• Nonlocal-jump state in native byte order

• C11/C17 language modes with GNU dialect support

• Statement expressions, case ranges, extension

• attribute, typeof, auto_type

• Builtins: __builtin_expect, __builtin_constant_p

• Bit operations: __builtin_popcount/clz/ctz/ffs/parity

• Byte swap: __builtin_bswap16/32/64

• Overflow: __builtin_add_overflow/sub/mul (generic and typed)

• Empty aggregates, alternate keyword spellings

• Compound literals in declarator initializers

• Compatible incomplete array / repeated block-scope extern

• MCS-51 family CI (compiler, assembler, UART smoke, full regression, QEMU)

• Windows x64 binary package (MSYS2 UCRT64) published as GitHub Release

• QEMU-based regression testing with deterministic icount

• MCS-251 ABI specification and instruction coverage

• GNU C and Zephyr compatibility status

• Chinese SDCC user manual

• Local Windows package build guide

• Peephole expansion: 480→714 lines (+18 rules)

  • WR merge, dptr reload elimination, push/pop adjacency, store-then-reload

• DPTR value tracking cache in loadDptrFromOperand

Based on upstream SDCC 4.6.0 (tag: upstream-sdcc-4.6.0)