From: Daniel Golle <daniel@makrotopia.org>
Subject: [PATCH] WTF: enable WebAssembly and BBQJIT on RISCV64

RISCV64 previously had ENABLE_WEBASSEMBLY=1 but ENABLE_WEBASSEMBLY_BBQJIT=0
and ENABLE_WEBASSEMBLY_OMGJIT=0. The LLInt-based wasm interpreter that used
to back this combination was replaced by the IPInt in-place interpreter,
which is not ported to RISCV64, so this configuration left no wasm execution
tier available and JSC aborted at startup with:

  INCOHERENT OPTIONS: at least one of useWasmIPInt, or useBBQJIT must be true

Turn ENABLE_WEBASSEMBLY_BBQJIT on for RISCV64 so BBQJIT becomes the wasm
execution tier on this architecture. IPInt and OMGJIT remain off.

The companion changes that make this safe at build- and run-time:
 * MacroAssemblerRISCV64.h gains noop SIMD stubs and hard-fault stubs for
   the wasm atomic MacroAssembler primitives that BBQJIT uses.
 * Options.cpp no longer forces useBBQJIT() = false on RISCV64.
 * Options.cpp already forces useWasmSIMD() = false on non-X86_64/ARM64
   architectures (and useSharedArrayBuffer defaults to false), so wasm
   SIMD codegen and wasm atomic codegen are never reached on RISCV64
   and their stubs are unreachable.

Signed-off-by: Daniel Golle <daniel@makrotopia.org>
--- a/Source/WTF/wtf/PlatformEnable.h
+++ b/Source/WTF/wtf/PlatformEnable.h
@@ -738,12 +738,28 @@
 #endif
 
 #if CPU(RISCV64)
+// RISCV64 wasm execution tiers:
+//   - IPInt (LLInt in-place interpreter): not ported; left disabled.
+//     LowLevelInterpreter.asm's IPInt call-trampoline labels are stubbed
+//     to crash() so the link still succeeds.
+//   - BBQJIT: enabled. The arch-conditional sites in WasmBBQJIT64.cpp
+//     that have no #else fall through to portable MacroAssembler
+//     primitives; the remaining gaps (wasm SIMD codegen, wasm atomics
+//     codegen) are addressed by gating both off at runtime:
+//       Options::useWasmSIMD = false (already set in Options.cpp for
+//       !X86_64 && !ARM64),
+//       Options::useSharedArrayBuffer = false (the default), which in
+//       turn keeps wasm atomic opcodes off the JIT codepath.
+//     MacroAssemblerRISCV64.h carries hard-fault stubs for the wasm
+//     atomic / SIMD MacroAssembler entry points so they trap loudly if
+//     the runtime gating is ever bypassed.
+//   - OMGJIT: not ported.
 #undef ENABLE_WEBASSEMBLY
 #define ENABLE_WEBASSEMBLY 1
 #undef ENABLE_WEBASSEMBLY_OMGJIT
 #define ENABLE_WEBASSEMBLY_OMGJIT 0
 #undef ENABLE_WEBASSEMBLY_BBQJIT
-#define ENABLE_WEBASSEMBLY_BBQJIT 0
+#define ENABLE_WEBASSEMBLY_BBQJIT 1
 #endif
 
 #if !defined(ENABLE_C_LOOP)