Bug 1406041: Add a fast-path for wasm code segment lookup; r=luke

MozReview-Commit-ID: L6LXvOOaNKs

--HG--
extra : rebase_source : c6efebdeba448366dd6f8adf740cbc167edadbbd
extra : amend_source : 07625d42aaadf3dc2e13176a66ad09bd7d705ea0

js/src/jit-test/tests/basic/testTypedArrayInit.js

@@ -11,9 +11,7 @@ function f() {
                      Float32Array,
                      Float64Array ])
   {
-    for (var len of [ 3, 30, 300, 3000 ]) {
-    // TODO: disabled before follow-up in bug 1406041
-    //for (var len of [ 3, 30, 300, 3000, 30000 ]) {
+    for (var len of [ 3, 30, 300, 3000, 30000 ]) {
       var arr = new ctor(len);
       for (var i = 0; i < arr.length; i++)
         assertEq(arr[i], 0, "index " + i + " of " + ctor.name + " len " + len);

js/src/jit/arm/Simulator-arm.cpp

@@ -1565,6 +1565,9 @@ Simulator::startWasmInterrupt(JitActivation* activation)
 void
 Simulator::handleWasmInterrupt()
 {
+    if (!wasm::CodeExists)
+        return;
+
     uint8_t* pc = (uint8_t*)get_pc();
     uint8_t* fp = (uint8_t*)get_register(r11);
 
@@ -1589,6 +1592,8 @@ Simulator::handleWasmInterrupt()
 bool
 Simulator::handleWasmFault(int32_t addr, unsigned numBytes)
 {
+    if (!wasm::CodeExists)
+        return false;
     if (!cx_->activation() || !cx_->activation()->isJit())
         return false;
     JitActivation* act = cx_->activation()->asJit();

js/src/jit/mips32/Simulator-mips32.cpp

@@ -1637,6 +1637,9 @@ Simulator::startInterrupt(JitActivation* activation)
 void
 Simulator::handleWasmInterrupt()
 {
+    if (!wasm::CodeExists)
+        return;
+
     void* pc = (void*)get_pc();
     void* fp = (void*)getRegister(Register::fp);
 
@@ -1663,6 +1666,9 @@ Simulator::handleWasmInterrupt()
 bool
 Simulator::handleWasmFault(int32_t addr, unsigned numBytes)
 {
+    if (!wasm::CodeExists)
+        return false;
+
     JSContext* cx = TlsContext.get();
     if (!cx->activation() || !cx->activation()->isJit())
         return false;

js/src/wasm/WasmProcess.cpp

@@ -38,6 +38,8 @@ using mozilla::BinarySearchIf;
 
 typedef Vector<const CodeSegment*, 0, SystemAllocPolicy> CodeSegmentVector;
 
+Atomic<bool> wasm::CodeExists(false);
+
 class ProcessCodeSegmentMap
 {
     // Since writes (insertions or removals) can happen on any background
@@ -134,6 +136,8 @@ class ProcessCodeSegmentMap
         if (!mutableCodeSegments_->insert(mutableCodeSegments_->begin() + index, cs))
             return false;
 
+        CodeExists = true;
+
         swapAndWait();
 
 #ifdef DEBUG
@@ -163,6 +167,9 @@ class ProcessCodeSegmentMap
 
         mutableCodeSegments_->erase(mutableCodeSegments_->begin() + index);
 
+        if (!mutableCodeSegments_->length())
+            CodeExists = false;
+
         swapAndWait();
 
 #ifdef DEBUG

js/src/wasm/WasmProcess.h

@@ -19,6 +19,8 @@
 #ifndef wasm_process_h
 #define wasm_process_h
 
+#include "mozilla/Atomics.h"
+
 namespace js {
 namespace wasm {
 
@@ -35,6 +37,11 @@ LookupCodeSegment(const void* pc);
 const Code*
 LookupCode(const void* pc);
 
+// A bool member that can be used as a very fast lookup to know if there is any
+// code segment at all.
+
+extern mozilla::Atomic<bool> CodeExists;
+
 // These methods allow to (un)register CodeSegments so they can be looked up
 // via pc in the methods described above.