Bug 1759909 - Enable AVX support for Wasm SIMD by default in Nightly. r=lth

Differential Revision: https://phabricator.services.mozilla.com/D141265

js/moz.configure

@@ -833,6 +833,54 @@ def wasm_simd(value, jit_enabled, simulator, cranelift_enabled, target):
 set_config("ENABLE_WASM_SIMD", wasm_simd)
 set_define("ENABLE_WASM_SIMD", wasm_simd)
 
+
+# Support for Intel AVX instruction.
+#
+# AVX is exclusively used in WebAssembly SIMD instructions at the moment:
+# set direct dependency on "--enable-wasm-simd".
+# =====================================================
+
+
+@depends(milestone.is_nightly, "--enable-wasm-simd", "--enable-simulator", target)
+def default_wasm_avx(is_nightly, wasm_simd_enabled, simulator, target):
+    if not wasm_simd_enabled:
+        return
+
+    if simulator:
+        return
+
+    if target.cpu in ("x86_64", "x86"):
+        return is_nightly
+
+
+option(
+    "--enable-wasm-avx",
+    default=default_wasm_avx,
+    help="{Enable|Disable} AVX support for WebAssembly SIMD",
+)
+
+
+@depends("--enable-wasm-avx", "--enable-wasm-simd", "--enable-simulator", target)
+def wasm_avx(value, wasm_simd_enabled, simulator, target):
+    if not value:
+        return
+
+    if not wasm_simd_enabled:
+        die("--enable-wasm-avx requires --enable-wasm-simd")
+
+    if simulator:
+        die("--enable-wasm-avx is not supported for simulators")
+
+    if target.cpu in ("x86_64", "x86"):
+        return True
+
+    die("--enable-wasm-avx only possible when targeting the x86_64/x86 jits")
+
+
+set_config("ENABLE_WASM_AVX", wasm_avx)
+set_define("ENABLE_WASM_AVX", wasm_avx)
+
+
 # Wormhole opcodes are Intel-only.  They are private to Firefox, but we need them for some
 # experiments on release and so they ride the trains.
 

js/public/Initialization.h

@@ -179,7 +179,7 @@ extern JS_PUBLIC_API void JS_ShutDown(void);
 namespace JS {
 // Enable support for AVX instructions in the JIT/Wasm backend on x86/x64
 // platforms. Must be called before JS_Init*.
-void SetAVXEnabled();
+void SetAVXEnabled(bool enabled);
 }  // namespace JS
 #endif
 

js/src/jit/x86-shared/Assembler-x86-shared.cpp

@@ -203,7 +203,11 @@ AssemblerX86Shared::DoubleCondition AssemblerX86Shared::InvertCondition(
 CPUInfo::SSEVersion CPUInfo::maxSSEVersion = UnknownSSE;
 CPUInfo::SSEVersion CPUInfo::maxEnabledSSEVersion = UnknownSSE;
 bool CPUInfo::avxPresent = false;
+#ifdef ENABLE_WASM_AVX
+bool CPUInfo::avxEnabled = true;
+#else
 bool CPUInfo::avxEnabled = false;
+#endif
 bool CPUInfo::popcntPresent = false;
 bool CPUInfo::bmi1Present = false;
 bool CPUInfo::bmi2Present = false;

js/src/jit/x86-shared/Assembler-x86-shared.h

@@ -263,6 +263,10 @@ class CPUInfo {
     SetMaxEnabledSSEVersion(SSE4_1);
     avxEnabled = false;
   }
+  static void SetAVXDisabled() {
+    MOZ_ASSERT(!FlagsHaveBeenComputed());
+    avxEnabled = false;
+  }
   static void SetAVXEnabled() {
     MOZ_ASSERT(!FlagsHaveBeenComputed());
     avxEnabled = true;

js/src/shell/js.cpp

@@ -12197,11 +12197,20 @@ int main(int argc, char** argv) {
           '\0', "no-sse42",
           "Pretend CPU does not support SSE4.2 instructions "
           "to test JIT codegen (no-op on platforms other than x86 and x64).") ||
+#ifdef ENABLE_WASM_AVX
+      !op.addBoolOption('\0', "enable-avx",
+                        "No-op. AVX is enabled by default, if available.") ||
+      !op.addBoolOption(
+          '\0', "no-avx",
+          "Pretend CPU does not support AVX or AVX2 instructions "
+          "to test JIT codegen (no-op on platforms other than x86 and x64).") ||
+#else
       !op.addBoolOption('\0', "enable-avx",
                         "AVX is disabled by default. Enable AVX. "
                         "(no-op on platforms other than x86 and x64).") ||
       !op.addBoolOption('\0', "no-avx",
                         "No-op. AVX is currently disabled by default.") ||
+#endif
       !op.addBoolOption('\0', "more-compartments",
                         "Make newGlobal default to creating a new "
                         "compartment.") ||
@@ -12389,6 +12398,12 @@ int main(int argc, char** argv) {
       return EXIT_FAILURE;
     }
   }
+  if (op.getBoolOption("no-avx")) {
+    js::jit::CPUInfo::SetAVXDisabled();
+    if (!sCompilerProcessFlags.append("--no-avx")) {
+      return EXIT_FAILURE;
+    }
+  }
   if (op.getBoolOption("enable-avx")) {
     js::jit::CPUInfo::SetAVXEnabled();
     if (!sCompilerProcessFlags.append("--enable-avx")) {

js/src/vm/Initialization.cpp

@@ -329,7 +329,13 @@ JS_PUBLIC_API bool JS_SetICUMemoryFunctions(JS_ICUAllocFn allocFn,
 
 #if defined(ENABLE_WASM_SIMD) && \
     (defined(JS_CODEGEN_X64) || defined(JS_CODEGEN_X86))
-void JS::SetAVXEnabled() { js::jit::CPUInfo::SetAVXEnabled(); }
+void JS::SetAVXEnabled(bool enabled) {
+  if (enabled) {
+    js::jit::CPUInfo::SetAVXEnabled();
+  } else {
+    js::jit::CPUInfo::SetAVXDisabled();
+  }
+}
 #endif
 
 JS_PUBLIC_API void JS::DisableJitBackend() {

modules/libpref/init/StaticPrefList.yaml

@@ -6802,7 +6802,7 @@
   # Changing these prefs requires a restart.
 -   name: javascript.options.wasm_simd_avx
     type: bool
-    value: false
+    value: @IS_NIGHTLY_BUILD@
     mirror: always
 #endif
 #endif

xpcom/build/XPCOMInit.cpp

@@ -256,9 +256,7 @@ static void InitializeJS() {
     (defined(JS_CODEGEN_X64) || defined(JS_CODEGEN_X86))
   // Update static engine preferences, such as AVX, before
   // `JS_InitWithFailureDiagnostic` is called.
-  if (mozilla::StaticPrefs::javascript_options_wasm_simd_avx()) {
-    JS::SetAVXEnabled();
-  }
+  JS::SetAVXEnabled(mozilla::StaticPrefs::javascript_options_wasm_simd_avx());
 #endif
 
   const char* jsInitFailureReason = JS_InitWithFailureDiagnostic();