From: Daniel Golle <daniel@makrotopia.org>
Subject: [PATCH] JavaScriptCore: declare BBQJIT ScratchScope for non-X86/non-ARM64 archs

WasmBBQJIT64.cpp's addSIMDShuffle and addSIMDShift declare a ScratchScope
named "scratches" only inside #if CPU(X86_64) / #elif CPU(ARM64), then
reference that name from "if constexpr (isX86())" blocks and other code
in the same function. In a non-template function, "if constexpr" does not
discard the false branch from name lookup (C++17 [stmt.if]p2), so on any
architecture not in that list the build fails with:

  error: 'scratches' was not declared in this scope

Add an #else branch in both functions declaring a ScratchScope with the
same template arity as the X86 path. wasm SIMD is gated off at runtime
on RISCV64 via Options::useWasmSIMD = false, so neither function is
reached and the new scratches declaration is unused at run time; it
only exists so the function bodies parse on RISCV64.

Signed-off-by: Daniel Golle <daniel@makrotopia.org>
--- a/Source/JavaScriptCore/wasm/WasmBBQJIT64.cpp
+++ b/Source/JavaScriptCore/wasm/WasmBBQJIT64.cpp
@@ -3442,6 +3442,11 @@ void BBQJIT::notifyFunctionUsesSIMD()
     clobber(ARM64Registers::q28);
     clobber(ARM64Registers::q29);
     ScratchScope<0, 0> scratches(*this, Location::fromFPR(ARM64Registers::q28), Location::fromFPR(ARM64Registers::q29));
+#else
+    // Other architectures (e.g. RISCV64) have no wasm SIMD codegen and
+    // never reach this function at runtime (useWasmSIMD is forced off).
+    // Declare scratches so the if-constexpr(isX86()) block below parses.
+    ScratchScope<0, 1> scratches(*this);
 #endif
     Location aLocation = loadIfNecessary(a);
     Location bLocation = loadIfNecessary(b);
@@ -3497,6 +3502,11 @@ void BBQJIT::notifyFunctionUsesSIMD()
     // Clobber and preserve RCX on x86, since we need it to do shifts.
     clobber(shiftRCX);
     ScratchScope<2, 2> scratches(*this, Location::fromGPR(shiftRCX));
+#elif !CPU(ARM64)
+    // RISCV64 / other archs: no wasm SIMD codegen exists; this function
+    // is unreachable at runtime via useWasmSIMD = false. Declare a
+    // ScratchScope so the X86-only sub-block below still parses.
+    ScratchScope<2, 2> scratches(*this);
 #endif
     Location srcLocation = loadIfNecessary(src);
     Location shiftLocation;