v0.2.1 — silicon-blocking i64 codegen fix

Silicon-blocking patch

Fixes #93: synth-compiled memset (and other compiler_builtins functions using i64 extend/wrap ops in their loop bodies) no longer hangs on real Cortex-M silicon.

Root cause

optimizer_bridge::wasm_to_ir had no handler for I64ExtendI32U / I64ExtendI32S / I32WrapI64. Their result vregs were never mapped to ARM registers, and the downstream get_arm_reg's silent R0 fallback caused subsequent i64 shifts to read R0 as their rm_lo/rm_hi — destroying memset's destination pointer on every iteration.

Symptoms

• Real STM32G474RE silicon hung at memset+0x4c during Zephyr's z_bss_zero.
• Synth-emitted memset was 454 bytes vs picolibc's ~80 bytes and looped forever.
• PC bounced between two addresses indefinitely, observed via OpenOCD halt+resume sampling.

Fix

Adds the three missing op handlers in wasm_to_ir + ir_to_arm + analyze_i64_local_gets. 5 regression tests added (3 of which fail-before-fix and pass-after).

This is the first concrete silicon-blocking instance of the "i64 lowering has multiple holes" pattern. Follow-up issues #103 (AAPCS clobber in I64SetCond, found by cargo-fuzz harness) and the latent vreg-mapping gap surfaced by the defensive-panic work track the broader class.

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v0.2.0 — RISC-V GA

First release with RV32IMAC as a first-class compilation target alongside ARM Cortex-M. Synth now emits real EM_RISCV ELF binaries and ships a complete bare-metal runtime (startup, linker script, PMP) for booting them.

RISC-V backend (new)

• New synth-backend-riscv crate with RV32IMAC encoder, ELF builder (EM_RISCV=0xF3), PMP allocator, instruction selector, bare-metal startup generator, and linker script generator.
• CLI: --backend riscv, --target riscv32imac/rv32imac/rv32i/rv32gc/rv64imac/rv64gc.
• New synth riscv-runtime command emits startup.c + linker.ld for cross-compilation.
• Selector covers the i32 surface (arithmetic, logic, shifts, comparisons, division with trap-on-zero), i32.load/store + sub-word load8/16 + store8/16, and control flow (block, loop, if/else, br, br_if). Locals for params 0..7.
• Encoder cross-validated against canonical RV32 hex encodings.
• Renode RV32IMAC platform (tests/renode/synth_riscv.repl) wired into Bazel CI.
• 98 backend-riscv tests, all passing.
• Offline integration smoke + end-to-end calculator demo.

What's still out of scope

• i64 lowering for RV32 (register-pair arithmetic — a future minor release).
• RV32F/D float instructions.
• br_table jump-table emission.
• Cross-function calls + relocations for multi-function module linking.
• RISC-V Rocq proofs (deferred until the validator-pattern work lands; see issue #76).

Compatibility

Purely additive. ARM Cortex-M codegen is unchanged. The RISC-V backend is gated behind --backend riscv. v0.1.x WAT compilation flows continue to work without modification.

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v0.1.1 — AAPCS regalloc fixes + Cortex-M7 hardening

Bug fixes (real-hardware-found)

• fix(opt): regalloc clobbers parameter registers in i64 ops — optimizer_bridge::ir_to_arm no longer hardcodes i64 ops to R0:R1 / R2:R3. New alloc_i64_pair picks free callee-saved pairs (R4..R11) skipping live param registers. Fixes silent corruption of i32 params when an i64 op runs before all params are read.
• fix(no-optimize): allocate stack frame + i64 local storage in select_with_stack — non-param locals now get a real stack frame, and i64 locals use 8-byte STR/LDR so the upper half doesn't get dropped. Fixes corruption of the callee-saved spill area.

Features

• feat(cli): --relocatable flag — forces ET_REL output even when the wasm has no imports, for linking into a host build system (e.g. Zephyr).
• feat(m7): Cortex-M7 hardware profiles
  • HardwareCapabilities::imxrt1062() — single-precision FPU, 16 MPU regions, 8 MB QSPI flash, 1 MB OCRAM
  • HardwareCapabilities::stm32h743() — double-precision FPU, 16 MPU regions, 2 MB Flash, 1 MB RAM
  • CLI --hardware {imxrt1062,stm32h743} and target-info wired up
  • Renode synth_cortex_m7.repl profile + cortex_m7_test.robot
  • MPU allocator tests proving 16-region operation on M7-class parts

Toolchain hygiene

• 8 clippy errors fixed (Rust 1.95 lint refresh): unnecessary_sort_by, collapsible_match, collapsible_if, manual_checked_division.

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