Bug 1706891 - Config machinery for relaxed simd. r=rhunt

Introduce moz.configure, WasmFeatures, and StaticPrefList.yaml
machinery to define a config option for relaxed SIMD
(https://github.com/WebAssembly/relaxed-simd).  At the moment, there
are no defined relaxed SIMD opcodes, but a dozen or so are in the
works.  This just sets us up for implementing those.

Differential Revision: https://phabricator.services.mozilla.com/D114117

js/moz.configure

@@ -804,6 +804,38 @@ set_config("ENABLE_WASM_SIMD_WORMHOLE", wasm_simd_wormhole)
 set_define("ENABLE_WASM_SIMD_WORMHOLE", wasm_simd_wormhole)
 
 
+# Support for WebAssembly relaxed SIMD
+# =====================================================
+
+
+@depends(milestone.is_nightly, "--enable-wasm-simd")
+def default_wasm_relaxed_simd(is_nightly, wasm_simd):
+    if is_nightly and wasm_simd:
+        return True
+
+
+option(
+    "--enable-wasm-relaxed-simd",
+    default=default_wasm_relaxed_simd,
+    help="{Enable|Disable} WebAssembly relaxed SIMD",
+)
+
+
+@depends("--enable-wasm-relaxed-simd", "--enable-wasm-simd")
+def wasm_relaxed_simd(value, wasm_simd):
+    if not value:
+        return
+
+    if not wasm_simd:
+        die("relaxed SIMD requires SIMD")
+
+    return True
+
+
+set_config("ENABLE_WASM_RELAXED_SIMD", wasm_relaxed_simd)
+set_define("ENABLE_WASM_RELAXED_SIMD", wasm_relaxed_simd)
+
+
 # Options for generating the shell as a script
 # ============================================
 option("--with-qemu-exe", nargs=1, help="Use path as an arm emulator on host platforms")

js/public/WasmFeatures.h

@@ -52,6 +52,11 @@
 #else
 #  define WASM_SIMD_ENABLED 0
 #endif
+#ifdef ENABLE_WASM_RELAXED_SIMD
+#  define WASM_RELAXED_SIMD_ENABLED 1
+#else
+#  define WASM_RELAXED_SIMD_ENABLED 0
+#endif
 #ifdef ENABLE_WASM_EXCEPTIONS
 #  define WASM_EXCEPTIONS_ENABLED 1
 #else
@@ -100,7 +105,16 @@
                /* compiler predicate */ BaselineAvailable(cx),                \
                /* flag predicate     */ WasmFunctionReferencesFlag(cx),       \
                /* shell flag         */ "gc",                                 \
-               /* preference name    */ "gc")
+               /* preference name    */ "gc")                                 \
+  EXPERIMENTAL(/* capitalized name   */ RelaxedSimd,                          \
+               /* lower case name    */ v128Relaxed,                          \
+               /* compile predicate  */ WASM_RELAXED_SIMD_ENABLED,            \
+               /* compiler predicate */ AnyCompilerAvailable(cx),             \
+               /* flag predicate     */ !IsFuzzingCranelift(cx) &&            \
+               js::jit::JitSupportsWasmSimd(),                                \
+               /* shell flag         */ "relaxed-simd",                       \
+               /* preference name    */ "relaxed_simd")
+
 // clang-format on
 
 #endif  // js_WasmFeatures_h

modules/libpref/init/StaticPrefList.yaml

@@ -5779,6 +5779,13 @@
     mirror: always
 #endif  // defined(ENABLE_WASM_SIMD)
 
+#if defined(ENABLE_WASM_RELAXED_SIMD)
+-   name: javascript.options.wasm_relaxed_simd
+    type: bool
+    value: false
+    mirror: always
+#endif  // defined(ENABLE_WASM_RELAXED_SIMD)
+
 #if defined(ENABLE_WASM_REFTYPES)
 -   name: javascript.options.wasm_reftypes
     type: bool