Changeset 102295 in webkit for trunk/Source/JavaScriptCore/wtf/Atomics.h

Timestamp:

Dec 7, 2011, 6:09:14 PM (13 years ago)

Author:

[email protected]

Message:

Compare and Swap should be enabled on ARMv7
​https://bugs.webkit.org/show_bug.cgi?id=74023

Reviewed by Geoff Garen.

Implemented weakCompareAndSwap in terms of LDREX/STREX and enabled PARALLEL_GC.
It gives the expected speed-up on multi-core ARMv7 devices.

• wtf/Atomics.h:

(WTF::weakCompareAndSwap):

• wtf/Platform.h:

File:

• trunk/Source/JavaScriptCore/wtf/Atomics.h (modified) (5 diffs)

trunk/Source/JavaScriptCore/wtf/Atomics.h

@@ -61 +61 @@
 
 #include "Platform.h"
+#include "StdLibExtras.h"
 #include "UnusedParam.h"
 
@@ -120 +121 @@
 inline bool weakCompareAndSwap(unsigned* location, unsigned expected, unsigned newValue)
 {
-    // FIXME: Implement COMPARE_AND_SWAP on other architectures and compilers. Currently
-    // it only works on X86 or X86_64 with a GCC-style compiler.
 #if ENABLE(COMPARE_AND_SWAP)
     bool result;
+#if CPU(X86) || CPU(X86_64)
     asm volatile(
         "lock; cmpxchgl %3, %2\n\t"
@@ -131 +131 @@
         : "memory"
         );
+#elif CPU(ARM_THUMB2)
+    unsigned tmp;
+    asm volatile(
+        "movw %1, #1\n\t"
+        "ldrex %2, %0\n\t"
+        "cmp %3, %2\n\t"
+        "bne.n 0f\n\t"
+        "strex %1, %4, %0\n\t"
+        "0:"
+        : "+m"(*location), "=&r"(result), "=&r"(tmp)
+        : "r"(expected), "r"(newValue)
+        : "memory");
+    result = !result;
+#else
+#error "Bad architecture for compare and swap."
+#endif
     return result;
 #else
@@ -143 +159 @@
 inline bool weakCompareAndSwap(void*volatile* location, void* expected, void* newValue)
 {
-    // FIXME: Implement COMPARE_AND_SWAP on other architectures and compilers. Currently
-    // it only works on X86 or X86_64 with a GCC-style compiler.
 #if ENABLE(COMPARE_AND_SWAP)
+#if CPU(X86_64)
     bool result;
     asm volatile(
-#if CPU(X86_64)
         "lock; cmpxchgq %3, %2\n\t"
-#else
-        "lock; cmpxchgl %3, %2\n\t"
-#endif
         "sete %1"
         : "+a"(expected), "=q"(result), "+m"(*location)
@@ -159 +170 @@
         );
     return result;
+#else
+    return weakCompareAndSwap(bitwise_cast<unsigned*>(location), bitwise_cast<unsigned>(expected), bitwise_cast<unsigned>(newValue));
+#endif
 #else // ENABLE(COMPARE_AND_SWAP)
     UNUSED_PARAM(location);