Simplify Push and PopContext instructions

There's no need for a temp register to store the old context in,
as PopContext can simply retrieve the old context from
the current one.

Change-Id: Ife9cfdff7fa8e47fc71e844a7798de88dbc79e26
Reviewed-by: Simon Hausmann <simon.hausmann@qt.io>

11 files changed, 60 insertions, 75 deletions

diff --git a/src/qml/compiler/qv4codegen.cpp b/src/qml/compiler/qv4codegen.cpp
index b46891572e..860a1307f2 100644
--- a/src/qml/compiler/qv4codegen.cpp
+++ b/src/qml/compiler/qv4codegen.cpp
@@ -2482,7 +2482,7 @@ int Codegen::defineFunction(const QString &name, AST::Node *ast,
 
     statementList(body);
 
-    _context->emitBlockFooter(this, -1);
+    _context->emitBlockFooter(this);
 
     if (hasError || !endsWithReturn(_module, body)) {
         bytecodeGenerator->setLocation(ast->lastSourceLocation());
diff --git a/src/qml/compiler/qv4compilercontext.cpp b/src/qml/compiler/qv4compilercontext.cpp
index bfe0d4b131..c4f7e51f6c 100644
--- a/src/qml/compiler/qv4compilercontext.cpp
+++ b/src/qml/compiler/qv4compilercontext.cpp
@@ -159,36 +159,32 @@ Context::ResolvedName Context::resolveName(const QString &name)
     return result;
 }
 
-int Context::emitBlockHeader(Codegen *codegen)
+void Context::emitBlockHeader(Codegen *codegen)
 {
     using Instruction = Moth::Instruction;
     Moth::BytecodeGenerator *bytecodeGenerator = codegen->generator();
 
     setupFunctionIndices(bytecodeGenerator);
-    int contextReg = -1;
 
-    if (requiresExecutionContext && blockIndex < 0) {
-        codegen->module()->blocks.append(this);
-        blockIndex = codegen->module()->blocks.count() - 1;
-    }
+    if (requiresExecutionContext) {
+        if (blockIndex < 0) {
+            codegen->module()->blocks.append(this);
+            blockIndex = codegen->module()->blocks.count() - 1;
+        }
 
-    if (requiresExecutionContext && contextType == ContextType::Global) {
-        Instruction::PushScriptContext scriptContext;
-        scriptContext.index = blockIndex;
-        bytecodeGenerator->addInstruction(scriptContext);
-    } else if (requiresExecutionContext ||
-        contextType == ContextType::Binding) { // we don't really need this for bindings, but we do for signal handlers, and we don't know if the code is a signal handler or not.
-        if (contextType == ContextType::Block || (contextType == ContextType::Eval && !isStrict)) {
+        if (contextType == ContextType::Global) {
+            Instruction::PushScriptContext scriptContext;
+            scriptContext.index = blockIndex;
+            bytecodeGenerator->addInstruction(scriptContext);
+        } else if (contextType == ContextType::Block || (contextType == ContextType::Eval && !isStrict)) {
             if (isCatchBlock) {
                 Instruction::PushCatchContext catchContext;
                 catchContext.index = blockIndex;
-                catchContext.reg = contextReg = bytecodeGenerator->newRegister();
                 catchContext.name = codegen->registerString(caughtVariable);
                 bytecodeGenerator->addInstruction(catchContext);
             } else {
                 Instruction::PushBlockContext blockContext;
                 blockContext.index = blockIndex;
-                blockContext.reg = contextReg = bytecodeGenerator->newRegister();
                 bytecodeGenerator->addInstruction(blockContext);
             }
         } else {
@@ -196,6 +192,7 @@ int Context::emitBlockHeader(Codegen *codegen)
             bytecodeGenerator->addInstruction(createContext);
         }
     }
+
     if (usesThis && !isStrict) {
         // make sure we convert this to an object
         Instruction::ConvertThisToObject convert;
@@ -250,25 +247,23 @@ int Context::emitBlockHeader(Codegen *codegen)
             r.storeConsumeAccumulator();
         }
     }
-
-    return contextReg;
 }
 
-void Context::emitBlockFooter(Codegen *codegen, int oldContextReg)
+void Context::emitBlockFooter(Codegen *codegen)
 {
     using Instruction = Moth::Instruction;
     Moth::BytecodeGenerator *bytecodeGenerator = codegen->generator();
 
-    if (requiresExecutionContext && contextType == ContextType::Global) {
+    if (!requiresExecutionContext)
+        return;
+
 QT_WARNING_PUSH
 QT_WARNING_DISABLE_GCC("-Wmaybe-uninitialized") // the loads below are empty structs.
+    if (contextType == ContextType::Global)
         bytecodeGenerator->addInstruction(Instruction::PopScriptContext());
+    else
+        bytecodeGenerator->addInstruction(Instruction::PopContext());
 QT_WARNING_POP
-    } else if (oldContextReg != -1) {
-        Instruction::PopContext popContext;
-        popContext.reg = oldContextReg;
-        bytecodeGenerator->addInstruction(popContext);
-    }
 }
 
 void Context::setupFunctionIndices(Moth::BytecodeGenerator *bytecodeGenerator)
diff --git a/src/qml/compiler/qv4compilercontext_p.h b/src/qml/compiler/qv4compilercontext_p.h
index 6838610d1c..95fca2c2c8 100644
--- a/src/qml/compiler/qv4compilercontext_p.h
+++ b/src/qml/compiler/qv4compilercontext_p.h
@@ -279,8 +279,8 @@ struct Context {
         bool isValid() const { return type != Unresolved; }
     };
     ResolvedName resolveName(const QString &name);
-    int emitBlockHeader(Compiler::Codegen *codegen);
-    void emitBlockFooter(Compiler::Codegen *codegen, int oldContextReg);
+    void emitBlockHeader(Compiler::Codegen *codegen);
+    void emitBlockFooter(Compiler::Codegen *codegen);
 
     void setupFunctionIndices(Moth::BytecodeGenerator *bytecodeGenerator);
 };
diff --git a/src/qml/compiler/qv4compilercontrolflow_p.h b/src/qml/compiler/qv4compilercontrolflow_p.h
index 89791330f9..db109533eb 100644
--- a/src/qml/compiler/qv4compilercontrolflow_p.h
+++ b/src/qml/compiler/qv4compilercontrolflow_p.h
@@ -306,11 +306,9 @@ struct ControlFlowWith : public ControlFlowUnwind
         : ControlFlowUnwind(cg, With)
     {
         setupExceptionHandler();
-        savedContextRegister = Moth::StackSlot::createRegister(generator()->newRegister());
 
         // assumes the with object is in the accumulator
         Instruction::PushWithContext pushScope;
-        pushScope.reg = savedContextRegister;
         generator()->addInstruction(pushScope);
         generator()->setExceptionHandler(&unwindLabel);
     }
@@ -321,12 +319,10 @@ struct ControlFlowWith : public ControlFlowUnwind
 
         generator()->setExceptionHandler(parentExceptionHandler());
         Instruction::PopContext pop;
-        pop.reg = savedContextRegister;
         generator()->addInstruction(pop);
 
         emitUnwindHandler();
     }
-    Moth::StackSlot savedContextRegister;
 };
 
 struct ControlFlowBlock : public ControlFlowUnwind
@@ -335,9 +331,9 @@ struct ControlFlowBlock : public ControlFlowUnwind
         : ControlFlowUnwind(cg, Block)
     {
         block = cg->enterBlock(ast);
-        savedContextRegister = block->emitBlockHeader(cg);
+        block->emitBlockHeader(cg);
 
-        if (savedContextRegister != -1) {
+        if (block->requiresExecutionContext) {
             setupExceptionHandler();
             generator()->setExceptionHandler(&unwindLabel);
         }
@@ -345,24 +341,23 @@ struct ControlFlowBlock : public ControlFlowUnwind
 
     virtual ~ControlFlowBlock() {
         // emit code for unwinding
-        if (savedContextRegister != -1) {
+        if (block->requiresExecutionContext ) {
             unwindLabel.link();
             generator()->setExceptionHandler(parentExceptionHandler());
         }
 
-        block->emitBlockFooter(cg, savedContextRegister);
+        block->emitBlockFooter(cg);
 
-        if (savedContextRegister != -1)
+        if (block->requiresExecutionContext )
             emitUnwindHandler();
         cg->leaveBlock();
     }
     virtual Handler getHandler(HandlerType type, const QString &label = QString()) {
-        if (savedContextRegister == -1)
+        if (!block->requiresExecutionContext )
             return getParentHandler(type, label);
         return ControlFlowUnwind::getHandler(type, label);
     }
 
-    int savedContextRegister = -1;
     Context *block;
 };
 
@@ -414,7 +409,7 @@ struct ControlFlowCatch : public ControlFlowUnwind
 
         Context *block = cg->enterBlock(catchExpression);
 
-        int savedContextReg = block->emitBlockHeader(cg);
+        block->emitBlockHeader(cg);
 
         // clear the unwind temp for exceptions, we want to resume normal code flow afterwards
         Reference::storeConstOnStack(cg, QV4::Encode::undefined(), controlFlowTemp);
@@ -430,7 +425,7 @@ struct ControlFlowCatch : public ControlFlowUnwind
 
         // exceptions inside catch and break/return statements go here
         catchUnwindLabel.link();
-        block->emitBlockFooter(cg, savedContextReg);
+        block->emitBlockFooter(cg);
 
         cg->leaveBlock();
 
diff --git a/src/qml/compiler/qv4instr_moth.cpp b/src/qml/compiler/qv4instr_moth.cpp
index 5e7fe816b2..95bc459df0 100644
--- a/src/qml/compiler/qv4instr_moth.cpp
+++ b/src/qml/compiler/qv4instr_moth.cpp
@@ -404,15 +404,14 @@ void dumpBytecode(const char *code, int len, int nLocals, int nFormals, int /*st
         MOTH_END_INSTR(CreateCallContext)
 
         MOTH_BEGIN_INSTR(PushCatchContext)
-            d << dumpRegister(reg, nFormals) << ", " << index << ", " << name;
+            d << index << ", " << name;
         MOTH_END_INSTR(PushCatchContext)
 
         MOTH_BEGIN_INSTR(PushWithContext)
-            d << dumpRegister(reg, nFormals);
         MOTH_END_INSTR(PushWithContext)
 
         MOTH_BEGIN_INSTR(PushBlockContext)
-            d << dumpRegister(reg, nFormals) << ", " << index;
+            d << index;
         MOTH_END_INSTR(PushBlockContext)
 
         MOTH_BEGIN_INSTR(CloneBlockContext)
@@ -426,7 +425,6 @@ void dumpBytecode(const char *code, int len, int nLocals, int nFormals, int /*st
         MOTH_END_INSTR(PopScriptContext)
 
         MOTH_BEGIN_INSTR(PopContext)
-            d << dumpRegister(reg, nFormals);
         MOTH_END_INSTR(PopContext)
 
         MOTH_BEGIN_INSTR(GetIterator)
diff --git a/src/qml/compiler/qv4instr_moth_p.h b/src/qml/compiler/qv4instr_moth_p.h
index 83ff11a128..54a7f5f13e 100644
--- a/src/qml/compiler/qv4instr_moth_p.h
+++ b/src/qml/compiler/qv4instr_moth_p.h
@@ -114,13 +114,13 @@ QT_BEGIN_NAMESPACE
 #define INSTR_GetException(op) INSTRUCTION(op, GetException, 0)
 #define INSTR_SetException(op) INSTRUCTION(op, SetException, 0)
 #define INSTR_CreateCallContext(op) INSTRUCTION(op, CreateCallContext, 0)
-#define INSTR_PushCatchContext(op) INSTRUCTION(op, PushCatchContext, 3, reg, index, name)
-#define INSTR_PushWithContext(op) INSTRUCTION(op, PushWithContext, 1, reg)
-#define INSTR_PushBlockContext(op) INSTRUCTION(op, PushBlockContext, 2, reg, index)
+#define INSTR_PushCatchContext(op) INSTRUCTION(op, PushCatchContext, 2, index, name)
+#define INSTR_PushWithContext(op) INSTRUCTION(op, PushWithContext, 0)
+#define INSTR_PushBlockContext(op) INSTRUCTION(op, PushBlockContext, 1, index)
 #define INSTR_CloneBlockContext(op) INSTRUCTION(op, CloneBlockContext, 0)
 #define INSTR_PushScriptContext(op) INSTRUCTION(op, PushScriptContext, 1, index)
 #define INSTR_PopScriptContext(op) INSTRUCTION(op, PopScriptContext, 0)
-#define INSTR_PopContext(op) INSTRUCTION(op, PopContext, 1, reg)
+#define INSTR_PopContext(op) INSTRUCTION(op, PopContext, 0)
 #define INSTR_GetIterator(op) INSTRUCTION(op, GetIterator, 1, iterator)
 #define INSTR_IteratorNext(op) INSTRUCTION(op, IteratorNext, 1, value)
 #define INSTR_IteratorClose(op) INSTRUCTION(op, IteratorClose, 1, done)
diff --git a/src/qml/jit/qv4assembler.cpp b/src/qml/jit/qv4assembler.cpp
index 736dfd0908..45dc87db19 100644
--- a/src/qml/jit/qv4assembler.cpp
+++ b/src/qml/jit/qv4assembler.cpp
@@ -2241,9 +2241,8 @@ void Assembler::clearExceptionHandler()
     pasm()->storePtr(TrustedImmPtr(nullptr), pasm()->exceptionHandlerAddress());
 }
 
-void Assembler::pushCatchContext(int reg, int index, int name)
+void Assembler::pushCatchContext(int index, int name)
 {
-    pasm()->copyReg(pasm()->contextAddress(), regAddr(reg));
     prepareCallWithArgCount(3);
     passInt32AsArg(name, 2);
     passInt32AsArg(index, 1);
@@ -2252,9 +2251,13 @@ void Assembler::pushCatchContext(int reg, int index, int name)
     pasm()->storeAccumulator(pasm()->contextAddress());
 }
 
-void Assembler::popContext(int reg)
+void Assembler::popContext()
 {
-    pasm()->copyReg(regAddr(reg), pasm()->contextAddress());
+    Heap::CallContext ctx;
+    Q_UNUSED(ctx)
+    pasm()->loadPointerFromValue(regAddr(CallData::Context), PlatformAssembler::ScratchRegister);
+    pasm()->loadAccumulator(Address(PlatformAssembler::ScratchRegister, ctx.outer.offset));
+    pasm()->storeAccumulator(regAddr(CallData::Context));
 }
 
 void Assembler::ret()
diff --git a/src/qml/jit/qv4assembler_p.h b/src/qml/jit/qv4assembler_p.h
index 99ae48e5ed..a1596e1640 100644
--- a/src/qml/jit/qv4assembler_p.h
+++ b/src/qml/jit/qv4assembler_p.h
@@ -164,8 +164,8 @@ public:
     void setException();
     void setExceptionHandler(int offset);
     void clearExceptionHandler();
-    void pushCatchContext(int reg, int index, int name);
-    void popContext(int reg);
+    void pushCatchContext(int index, int name);
+    void popContext();
 
     // other stuff
     void ret();
diff --git a/src/qml/jit/qv4jit.cpp b/src/qml/jit/qv4jit.cpp
index 15ece7e903..2bc60bff70 100644
--- a/src/qml/jit/qv4jit.cpp
+++ b/src/qml/jit/qv4jit.cpp
@@ -617,44 +617,40 @@ void BaselineJIT::generate_CreateCallContext()
     as->storeHeapObject(CallData::Context);
 }
 
-void BaselineJIT::generate_PushCatchContext(int reg, int index, int name) { as->pushCatchContext(reg, index, name); }
+void BaselineJIT::generate_PushCatchContext(int index, int name) { as->pushCatchContext(index, name); }
 
-static void pushWithContextHelper(ExecutionEngine *engine, QV4::Value *stack, int reg)
+static void pushWithContextHelper(ExecutionEngine *engine, QV4::Value *stack)
 {
     QV4::Value &accumulator = stack[CallData::Accumulator];
     accumulator = accumulator.toObject(engine);
     if (engine->hasException)
         return;
-    stack[reg] = stack[CallData::Context];
     ExecutionContext *c = static_cast<ExecutionContext *>(stack + CallData::Context);
     stack[CallData::Context] = Runtime::method_createWithContext(c, accumulator);
 }
 
-void BaselineJIT::generate_PushWithContext(int reg)
+void BaselineJIT::generate_PushWithContext()
 {
     STORE_IP();
     as->saveAccumulatorInFrame();
-    as->prepareCallWithArgCount(3);
-    as->passInt32AsArg(reg, 2);
+    as->prepareCallWithArgCount(2);
     as->passRegAsArg(0, 1);
     as->passEngineAsArg(0);
     JIT_GENERATE_RUNTIME_CALL(pushWithContextHelper, Assembler::IgnoreResult);
     as->checkException();
 }
 
-static void pushBlockContextHelper(QV4::Value *stack, int reg, int index)
+static void pushBlockContextHelper(QV4::Value *stack, int index)
 {
-    stack[reg] = stack[CallData::Context];
     ExecutionContext *c = static_cast<ExecutionContext *>(stack + CallData::Context);
     stack[CallData::Context] = Runtime::method_createBlockContext(c, index);
 }
 
-void BaselineJIT::generate_PushBlockContext(int reg, int index)
+void BaselineJIT::generate_PushBlockContext(int index)
 {
     as->saveAccumulatorInFrame();
-    as->prepareCallWithArgCount(3);
-    as->passInt32AsArg(index, 2);
-    as->passInt32AsArg(reg, 1);
+    as->prepareCallWithArgCount(2);
+    as->passInt32AsArg(index, 1);
     as->passRegAsArg(0, 0);
     JIT_GENERATE_RUNTIME_CALL(pushBlockContextHelper, Assembler::IgnoreResult);
 }
@@ -701,7 +697,7 @@ void BaselineJIT::generate_PopScriptContext()
     JIT_GENERATE_RUNTIME_CALL(popScriptContextHelper, Assembler::IgnoreResult);
 }
 
-void BaselineJIT::generate_PopContext(int reg) { as->popContext(reg); }
+void BaselineJIT::generate_PopContext() { as->popContext(); }
 
 void BaselineJIT::generate_GetIterator(int iterator)
 {
diff --git a/src/qml/jit/qv4jit_p.h b/src/qml/jit/qv4jit_p.h
index d48041d954..8aa0cb430e 100644
--- a/src/qml/jit/qv4jit_p.h
+++ b/src/qml/jit/qv4jit_p.h
@@ -178,13 +178,13 @@ public:
     void generate_GetException() override;
     void generate_SetException() override;
     void generate_CreateCallContext() override;
-    void generate_PushCatchContext(int reg, int index, int name) override;
-    void generate_PushWithContext(int reg) override;
-    void generate_PushBlockContext(int reg, int index) override;
+    void generate_PushCatchContext(int index, int name) override;
+    void generate_PushWithContext() override;
+    void generate_PushBlockContext(int index) override;
     void generate_CloneBlockContext() override;
     void generate_PushScriptContext(int index) override;
     void generate_PopScriptContext() override;
-    void generate_PopContext(int reg) override;
+    void generate_PopContext() override;
     void generate_GetIterator(int iterator) override;
     void generate_IteratorNext(int value) override;
     void generate_IteratorClose(int done) override;
diff --git a/src/qml/jsruntime/qv4vme_moth.cpp b/src/qml/jsruntime/qv4vme_moth.cpp
index f39fd39a98..84d5d6e6e4 100644
--- a/src/qml/jsruntime/qv4vme_moth.cpp
+++ b/src/qml/jsruntime/qv4vme_moth.cpp
@@ -909,7 +909,6 @@ QV4::ReturnedValue VME::interpret(CppStackFrame &frame, const uchar *code)
     MOTH_END_INSTR(SetException)
 
     MOTH_BEGIN_INSTR(PushCatchContext)
-        STACK_VALUE(reg) = STACK_VALUE(CallData::Context);
         ExecutionContext *c = static_cast<ExecutionContext *>(stack + CallData::Context);
         STACK_VALUE(CallData::Context) = Runtime::method_createCatchContext(c, index, name);
     MOTH_END_INSTR(PushCatchContext)
@@ -923,14 +922,12 @@ QV4::ReturnedValue VME::interpret(CppStackFrame &frame, const uchar *code)
         STORE_ACC();
         accumulator = accumulator.toObject(engine);
         CHECK_EXCEPTION;
-        STACK_VALUE(reg) = STACK_VALUE(CallData::Context);
         ExecutionContext *c = static_cast<ExecutionContext *>(stack + CallData::Context);
         STACK_VALUE(CallData::Context) = Runtime::method_createWithContext(c, accumulator);
     MOTH_END_INSTR(PushWithContext)
 
     MOTH_BEGIN_INSTR(PushBlockContext)
         STORE_ACC();
-        STACK_VALUE(reg) = STACK_VALUE(CallData::Context);
         ExecutionContext *c = static_cast<ExecutionContext *>(stack + CallData::Context);
         STACK_VALUE(CallData::Context) = Runtime::method_createBlockContext(c, index);
     MOTH_END_INSTR(PushBlockContext)
@@ -950,7 +947,8 @@ QV4::ReturnedValue VME::interpret(CppStackFrame &frame, const uchar *code)
     MOTH_END_INSTR(PopScriptContext)
 
     MOTH_BEGIN_INSTR(PopContext)
-        STACK_VALUE(CallData::Context) = STACK_VALUE(reg);
+        ExecutionContext *c = static_cast<ExecutionContext *>(stack + CallData::Context);
+        STACK_VALUE(CallData::Context) = c->d()->outer;
     MOTH_END_INSTR(PopContext)
 
     MOTH_BEGIN_INSTR(GetIterator)