Changeset 192599 in webkit

Timestamp:

Nov 18, 2015 4:30:37 PM (8 years ago)

Author:

mark.lam@apple.com

Message:

Remove some unnecessary jumps in snippet code.
​https://bugs.webkit.org/show_bug.cgi?id=151415

Reviewed by Geoffrey Garen.

Previously, the snippet generators always emit a jump at the end of the fast
path. In the baseline JIT and FTL, this results in a jump to the very next
instruction. I've change it to assume that the fast path will just fall thru,
and let the client decide instead if it wants/needs a jump or not after the fast
path.

I also changed the generators to provide a didEmitFastPath() query explicitly
declare if they actually generated the fast path, instead of having the client
infer it from an empty endJumpList.

Benchmarks show that perf is neutral with this change (tested on x86_64).

• dfg/DFGSpeculativeJIT.cpp:

(JSC::DFG::SpeculativeJIT::compileValueAdd):
(JSC::DFG::SpeculativeJIT::compileArithSub):

• ftl/FTLCompile.cpp:

(JSC::FTL::mmAllocateDataSection):

• jit/JITAddGenerator.cpp:

(JSC::JITAddGenerator::generateFastPath):

• jit/JITAddGenerator.h:

(JSC::JITAddGenerator::didEmitFastPath):
(JSC::JITAddGenerator::endJumpList):
(JSC::JITAddGenerator::slowPathJumpList):

• jit/JITArithmetic.cpp:

(JSC::JIT::emit_op_add):
(JSC::JIT::emit_op_sub):

• jit/JITSubGenerator.cpp:

(JSC::JITSubGenerator::generateFastPath):

• jit/JITSubGenerator.h:

(JSC::JITSubGenerator::didEmitFastPath):
(JSC::JITSubGenerator::endJumpList):
(JSC::JITSubGenerator::slowPathJumpList):

Location:

trunk/Source/JavaScriptCore

Files:

• ChangeLog (modified) (1 diff)
• dfg/DFGSpeculativeJIT.cpp (modified) (2 diffs)
• ftl/FTLCompile.cpp (modified) (1 diff)
• jit/JITAddGenerator.cpp (modified) (2 diffs)
• jit/JITAddGenerator.h (modified) (2 diffs)
• jit/JITArithmetic.cpp (modified) (3 diffs)
• jit/JITSubGenerator.cpp (modified) (2 diffs)
• jit/JITSubGenerator.h (modified) (2 diffs)

trunk/Source/JavaScriptCore/ChangeLog

@@ +1 @@
+2015-11-18  Mark Lam  <mark.lam@apple.com>
+
+        Remove some unnecessary jumps in snippet code.
+        https://bugs.webkit.org/show_bug.cgi?id=151415
+
+        Reviewed by Geoffrey Garen.
+
+        Previously, the snippet generators always emit a jump at the end of the fast
+        path.  In the baseline JIT and FTL, this results in a jump to the very next
+        instruction.  I've change it to assume that the fast path will just fall thru,
+        and let the client decide instead if it wants/needs a jump or not after the fast
+        path.
+
+        I also changed the generators to provide a didEmitFastPath() query explicitly
+        declare if they actually generated the fast path, instead of having the client
+        infer it from an empty endJumpList.
+
+        Benchmarks show that perf is neutral with this change (tested on x86_64).
+
+        * dfg/DFGSpeculativeJIT.cpp:
+        (JSC::DFG::SpeculativeJIT::compileValueAdd):
+        (JSC::DFG::SpeculativeJIT::compileArithSub):
+        * ftl/FTLCompile.cpp:
+        (JSC::FTL::mmAllocateDataSection):
+        * jit/JITAddGenerator.cpp:
+        (JSC::JITAddGenerator::generateFastPath):
+        * jit/JITAddGenerator.h:
+        (JSC::JITAddGenerator::didEmitFastPath):
+        (JSC::JITAddGenerator::endJumpList):
+        (JSC::JITAddGenerator::slowPathJumpList):
+        * jit/JITArithmetic.cpp:
+        (JSC::JIT::emit_op_add):
+        (JSC::JIT::emit_op_sub):
+        * jit/JITSubGenerator.cpp:
+        (JSC::JITSubGenerator::generateFastPath):
+        * jit/JITSubGenerator.h:
+        (JSC::JITSubGenerator::didEmitFastPath):
+        (JSC::JITSubGenerator::endJumpList):
+        (JSC::JITSubGenerator::slowPathJumpList):
+
 2015-11-18  Commit Queue  <commit-queue@webkit.org>
 

trunk/Source/JavaScriptCore/dfg/DFGSpeculativeJIT.cpp

@@ -2881 +2881 @@
     gen.generateFastPath(m_jit);
 
+    ASSERT(gen.didEmitFastPath());
+    gen.endJumpList().append(m_jit.jump());
+
     gen.slowPathJumpList().link(&m_jit);
 
@@ -3240 +3243 @@
             leftFPR, rightFPR, scratchGPR, scratchFPR);
         gen.generateFastPath(m_jit);
+
+        ASSERT(gen.didEmitFastPath());
+        gen.endJumpList().append(m_jit.jump());
 
         gen.slowPathJumpList().link(&m_jit);

trunk/Source/JavaScriptCore/ftl/FTLCompile.cpp

@@ -463 +463 @@
         gen.generateFastPath(fastPathJIT);
 
+        ASSERT(gen.didEmitFastPath());
         gen.endJumpList().link(&fastPathJIT);
         context.restoreRegisters(fastPathJIT);

trunk/Source/JavaScriptCore/jit/JITAddGenerator.cpp

@@ -45 +45 @@
     
     if (!m_leftType.mightBeNumber() || !m_rightType.mightBeNumber()) {
-        m_slowPathJumpList.append(jit.jump());
+        ASSERT(!m_didEmitFastPath);
         return;
     }
+
+    m_didEmitFastPath = true;
 
     if (m_leftIsConstInt32 || m_rightIsConstInt32) {
@@ -138 +140 @@
     jit.addDouble(m_rightFPR, m_leftFPR);
     jit.boxDouble(m_leftFPR, m_result);
-
-    m_endJumpList.append(jit.jump());
 }
 

trunk/Source/JavaScriptCore/jit/JITAddGenerator.h

@@ -59 +59 @@
     void generateFastPath(CCallHelpers&);
 
+    bool didEmitFastPath() const { return m_didEmitFastPath; }
     CCallHelpers::JumpList endJumpList() { return m_endJumpList; }
     CCallHelpers::JumpList slowPathJumpList() { return m_slowPathJumpList; }
@@ -76 +77 @@
     GPRReg m_scratchGPR;
     FPRReg m_scratchFPR;
+    bool m_didEmitFastPath { false };
 
     CCallHelpers::JumpList m_endJumpList;

trunk/Source/JavaScriptCore/jit/JITArithmetic.cpp

@@ -959 +959 @@
     gen.generateFastPath(*this);
 
-    if (!gen.endJumpList().empty()) {
+    if (gen.didEmitFastPath()) {
         gen.endJumpList().link(this);
         emitPutVirtualRegister(result, resultRegs);
@@ -965 +965 @@
         addSlowCase(gen.slowPathJumpList());
     } else {
-        gen.slowPathJumpList().link(this);
+        ASSERT(gen.endJumpList().empty());
+        ASSERT(gen.slowPathJumpList().empty());
         JITSlowPathCall slowPathCall(this, currentInstruction, slow_path_add);
         slowPathCall.call();
@@ -1007 +1008 @@
 
     gen.generateFastPath(*this);
+
+    ASSERT(gen.didEmitFastPath());
     gen.endJumpList().link(this);
     emitPutVirtualRegister(result, resultRegs);

trunk/Source/JavaScriptCore/jit/JITSubGenerator.cpp

@@ -41 +41 @@
     ASSERT(m_scratchFPR != InvalidFPRReg);
 #endif
+
+    m_didEmitFastPath = true;
+
     CCallHelpers::Jump leftNotInt = jit.branchIfNotInt32(m_left);
     CCallHelpers::Jump rightNotInt = jit.branchIfNotInt32(m_right);
@@ -82 +85 @@
     jit.subDouble(m_rightFPR, m_leftFPR);
     jit.boxDouble(m_leftFPR, m_result);
-
-    m_endJumpList.append(jit.jump());
 }
 

trunk/Source/JavaScriptCore/jit/JITSubGenerator.h

@@ -52 +52 @@
     void generateFastPath(CCallHelpers&);
 
+    bool didEmitFastPath() const { return m_didEmitFastPath; }
     CCallHelpers::JumpList endJumpList() { return m_endJumpList; }
     CCallHelpers::JumpList slowPathJumpList() { return m_slowPathJumpList; }
@@ -65 +66 @@
     GPRReg m_scratchGPR;
     FPRReg m_scratchFPR;
+    bool m_didEmitFastPath { false };
 
     CCallHelpers::JumpList m_endJumpList;