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Compilers construction DD2488 lecture 2
Torbj¨
- rn Granlund Nada, tg@gmplib.org
Compilers construction DD2488 lecture 2
Torbj¨
- rn Granlund Nada, tg@gmplib.org
Compilers construction DD2488 lecture 2 Torbj orn Granlund Nada, - - PowerPoint PPT Presentation
Compilers construction DD2488 lecture 2 Torbj orn Granlund Nada, - - PowerPoint PPT Presentation
Compilers construction DD2488 lecture 2 Torbj orn Granlund Nada, tg@gmplib.org Compilers construction DD2488 lecture 2 Torbj orn Granlund Nada, tg@gmplib.org These slides will be available from the course web page Course news Please
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Course news
Please see course web page for news Informal session 2 scheduled (Mon, Wed in two weeks) New milestones set for session 2
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Today’s subjects
◮ Activation records ◮ Translation to intermediate code
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PART1: Activation records
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The ”Stack”
The stack is main abstraction for method calls
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The ”Stack”
The stack is main abstraction for method calls
◮ Typically grows downwards
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The ”Stack”
The stack is main abstraction for method calls
◮ Typically grows downwards ◮ Operations: PUSH and POP
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The ”Stack”
The stack is main abstraction for method calls
◮ Typically grows downwards ◮ Operations: PUSH and POP ◮ Stack pointer points at last item PUSHed
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The ”Stack”
The stack is main abstraction for method calls
◮ Typically grows downwards ◮ Operations: PUSH and POP ◮ Stack pointer points at last item PUSHed ◮ Stack pointer is special CPU register
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The ”Stack”
The stack is main abstraction for method calls
◮ Typically grows downwards ◮ Operations: PUSH and POP ◮ Stack pointer points at last item PUSHed ◮ Stack pointer is special CPU register ◮ Operating systems supports the stack
.
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Activation records
Activation record = data a method needs during execution and for returning to its caller
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Activation records
Activation record = data a method needs during execution and for returning to its caller Activation records live on the stack
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Activation records
Activation record = data a method needs during execution and for returning to its caller Activation records live on the stack In fact, activation records are the only thing there Contents:
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Activation records
Activation record = data a method needs during execution and for returning to its caller Activation records live on the stack In fact, activation records are the only thing there Contents:
◮ Incoming parameters
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Activation records
Activation record = data a method needs during execution and for returning to its caller Activation records live on the stack In fact, activation records are the only thing there Contents:
◮ Incoming parameters ◮ Return address
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Activation records
Activation record = data a method needs during execution and for returning to its caller Activation records live on the stack In fact, activation records are the only thing there Contents:
◮ Incoming parameters ◮ Return address ◮ Register save area
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Activation records
Activation record = data a method needs during execution and for returning to its caller Activation records live on the stack In fact, activation records are the only thing there Contents:
◮ Incoming parameters ◮ Return address ◮ Register save area ◮ Space for local variables
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Activation records
Activation record = data a method needs during execution and for returning to its caller Activation records live on the stack In fact, activation records are the only thing there Contents:
◮ Incoming parameters ◮ Return address ◮ Register save area ◮ Space for local variables ◮ Space for compiler-generated temporaries
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Activation records
Activation record = data a method needs during execution and for returning to its caller Activation records live on the stack In fact, activation records are the only thing there Contents:
◮ Incoming parameters ◮ Return address ◮ Register save area ◮ Space for local variables ◮ Space for compiler-generated temporaries ◮ Static link
.
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lower addresses . . . . .
- utgoing
arguments incoming arguments local variables saved registers return address argument n argument 1 static link next frame argument n argument 1 static link frame pointer stack pointer current frame previous frame higher addresses .
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Managing activation records
The generated code must manage activation records For JVM: Higher abstraction level—details in its documentation For ASM: Lower abstraction level—follow ”ABI”
◮ Compiler computes exact layout ◮ Compiler generates instructions for adjusting stack pointer,
saving registers, updating static link, etc.
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Static nesting—variable access
long factorial (long n) { long bar (long i) { if (i == n) return n; else return i * bar (i + 1); } return bar (1); }
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PART2: Translation to Intermediate Representation
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Compiler passes
text lex tokens tokens parse parse tree + symtab parse tree + symtab semantic analysis parse tree + symtab parse tree + symtab canonicalise IR IR flow analysis IR + dependency graph IR ”optimisations” IR IR instruction selection ASM with ∞ # of regs ASM register allocation ASM ASM allocation fixup ASM ASM stack layout ASM ASM code emission
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Translation to Intermediate Representation (IR)
IN: Parse tree (and symbol table(s) with type info) OUT: Abstract Intermediate Representation What are the differences between PT and IR?
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Translation to Intermediate Representation (IR)
IN: Parse tree (and symbol table(s) with type info) OUT: Abstract Intermediate Representation What are the differences between PT and IR?
◮ Parse tree depends on source language, IR is source language
independent
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Translation to Intermediate Representation (IR)
IN: Parse tree (and symbol table(s) with type info) OUT: Abstract Intermediate Representation What are the differences between PT and IR?
◮ Parse tree depends on source language, IR is source language
independent
◮ IR ”portable assembly”
.
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Intermediate Representation properties
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Intermediate Representation properties
◮ Convenient for parse tree visitor to generate
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Intermediate Representation properties
◮ Convenient for parse tree visitor to generate ◮ Convenient to translate to actual assembly code
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Intermediate Representation properties
◮ Convenient for parse tree visitor to generate ◮ Convenient to translate to actual assembly code ◮ Allow analysis in optimising compiler
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Intermediate Representation properties
◮ Convenient for parse tree visitor to generate ◮ Convenient to translate to actual assembly code ◮ Allow analysis in optimising compiler ◮ Start as a full tree, gradually shallowed
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Intermediate Representation properties
◮ Convenient for parse tree visitor to generate ◮ Convenient to translate to actual assembly code ◮ Allow analysis in optimising compiler ◮ Start as a full tree, gradually shallowed ◮ Infinite number of registers
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Intermediate Representation properties
◮ Convenient for parse tree visitor to generate ◮ Convenient to translate to actual assembly code ◮ Allow analysis in optimising compiler ◮ Start as a full tree, gradually shallowed ◮ Infinite number of registers
GCC uses two IR’s, ”Tree” and ”RTL”
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Translation to IR—issues
Plain expressions are easy, right? x = y + z * (a + b - t * t) * (b + 4711)
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Translation to IR—issues
Plain expressions are easy, right? x = y + z * (a + b - t * t) * (b + 4711) But how about this? x = y + z * (a + factorial(17) - t * t) * ((b++) + binom(n,k))
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Translation to IR—issues
Plain expressions are easy, right? x = y + z * (a + b - t * t) * (b + 4711) But how about this? x = y + z * (a + factorial(17) - t * t) * ((b++) + binom(n,k)) Conclusion: We have deal with side effects!
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Translation to IR—issues
Plain expressions are easy, right? x = y + z * (a + b - t * t) * (b + 4711) But how about this? x = y + z * (a + factorial(17) - t * t) * ((b++) + binom(n,k)) Conclusion: We have deal with side effects! Which side-effects exist is language-dependent In Java: function calls and increments In C: function calls, increments, and nested assignments (yuk)
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Mangling IR
Directly after translation, statements in IR will closely reflect statements in source code program
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Mangling IR
Directly after translation, statements in IR will closely reflect statements in source code program We gradually break this down to simpler but more statements
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Mangling IR
Directly after translation, statements in IR will closely reflect statements in source code program We gradually break this down to simpler but more statements In the end, we have statements that are close to assembly code, with side effects sequenced correctly
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