Questions tagged [compilers]

Questions about programs that read code in one language (source language) and translate it into an equivalent program in another language (target language).

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Why the grammar is not (LL1)?

Why the grammar is not (LL1)? (e is the epsilon) $$S \to a A \mid b B \mid a C c $$ $$A \to a A \mid a a A \mid e $$ $$B \to c C \mid D \mid e $$ CHOICE 1: The grammar is Left-Recursive (LR) CHOICE 2: ...
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How do you create a sentential form in a given grammar?

I am given the following grammar: $$S ::= aBS| abT |a$$ $$T::= d | dT$$$$B ::= da | ϵ | S$$ I need to decide whether $aBaabda$ can be produced in the given grammar. I am unsure how the grammar can ...
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Is there a simple algorithm for generating unit tests given a function's code? [closed]

Given the abstract syntax tree (AST) of each line of a function's code, I am asked to generate code for that function's corresponding unit tests, similar to what Microsoft's IntelliTest tool does here:...
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Data space progress - Compilers

Consider a programming language that supports (a) nested subroutine statements with static binding and (b) value-by-reference parameterization and by name, with corresponding keywords val, var and ...
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What kind of binary compatibility is present for 2 processors sharing an Instruction Set?

Consider Intel x86 and AMD x86 Processors. As I understand, since they use the same Instruction Set, in theory an application compiled for Intel x86 processor would run without any modification on ...
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How to determine valid handle for given bottom up parser?

I came across following question: Consider the grammar: $E → E + n\text{ | }E × n\text{ | }n$ For a sentence n + n × n, the handles in the right-sentential form of the reduction are (...
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47 views

Variable name starting with integers

When I started doing programming I wondered that why the variable names can't start with integer. Back then I accepted that , may be this is how the compiler designers have decided to go with. But now ...
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45 views

Removing left recursion with terminals only

I have a grammar: $G → id > id$    $| id < id$    $| G and id$ Does anybody know how I can do left recursive elimination on this one, when it doesn't have any extra non terminals?
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How are lexical tokens produced

I am studying Compiler Design. The instructor told us that when a program is given to lexical analyzer it find all tokens then a symbol table is created and it is updated at every phase accordingly, ...
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left/right derivations of grammars and parse trees

I'm having a hard time understanding how left/right derivations work. I have a very simple example that I've attempted but I don't really know how to check if it's correct. $S-> NP$ $V$ $NP$ $NP -&...
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Left recursive grammar to right recursive grammar

I am studying conversion from left recursive grammar to right recursive grammar. The given grammar is $$E \to E + T \mid T $$ It's equivalent right recursive grammar will be $$\begin{align}E &\to ...
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What assigns the physical addresses to variables?

Earlier I was having a technical test when I stumbled across this question: I know that probably in modern systems, the OS and the MMU is responsible for that. But the test was focused on Embedded ...
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How does software prefetching work with in order processors?

From prof. Onut Mutlu's slides on prefetching, this example has been shown as software prefetching: ...
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How is a program stored before compiling?

When we write code, after compilation the code will be converted to machine language and then stored in the hard disk. But before compiling the code, it is still in the high-level language. How and ...
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441 views

Is this an LL(1) grammar? How to solve First - Follow conflict?

im trying to check if this grammar is LL(1). S -> L = R L -> * L | id R -> L | R + R | num As you can see there is a Left recursion on R production. So i remove that and what i get is: S -> L = ...
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Calculating ring inequalities with fixed precision

Suppose we are given $n$ $M$-bit (the word size of the computer) integers $x_i$, and wish to calculate a linear or nonlinear inequality involving the numbers (an expression made up from the $x_i$, ...
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How compiler optimizations create irreducible control flow graph?

I've been looking through research papers and the internet and found many claims that "compiler optimizations can cause irreducible control flow". However, I was not able to find a single ...
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Does strong typing contribute to better performance optimization by compiler?

Do guarantees provided by the type systems enable better performance optimizations by the modern compilers? I found a 20+ year article suggesting that it would. Also, intuitively speaking, knowing ...
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Inference and Unification algorithm provided to a Unification graph of two expressions

I am trying to unify two expressions given a unification algorithm $unify$ applied to the unification graph of the two expressions. However, I struggle a lot in understanding how exactly the steps of ...
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How LR parser works with grammar containing epsilon productions

In Dragon book for compiler design there is this example of SDT in Example 5.16 $L\rightarrow En$ $E\rightarrow \{ print (' +') ; \} \space E_1 + T$ $E\rightarrow T$ $T\rightarrow \{ print (' *' ) ; ...
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How is CLR(1) grammar more powerful than LALR(1) grammar

I am unable to understand how Canonical LR(1) grammar is more powerful than LookAhead LR(1). Both have lookahead symbols in their items and works almost similarly, so how can CLR(1) derive a larger ...
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Representing abstract syntax tree as a graph

Does it make sense to represent an AST as a graph? How can one achieve a mapping between ASTs and graphs that preserves both semantic and syntactic properties of source code? The goal and application ...
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PDA translating $a^{m+n} b^n$ to $x^{2m+2} y^{3n}$

On my compilation theory exam we had the following problem: Construct a PDA translator (just one stack) such that it translates the language $$ a^{m+n}b^n \rightarrow x^{2m+2}y^{3n}, \text{ where } n,...
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virtual machine based programming languages vs low level

I took programming lecture it was about C/java and how to build compilers, so I wanted to know. As far I see, languages like Java/C# are developing their virtual machine CLR/JVM with good base and are ...
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Can Yacc be used to generate three address code for Java 1?

I have read that yacc generates bottom up parser for LALR(1) grammars. I have a grammar for Java 1 that can be used for generating three address code and is strictly LALR(1), but the translation ...
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What other implementation styles are there besides compilation, interpretation and transpilation?

Obviously there is JIT but it is basically run-time compilation. There is also implementing things in VHDL or ASIC. But my question is more towards software techniques for program building and ...
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239 views

How to translate automatons (Turing machines) into programs of high level programming language?

Every program in high level ("industrial") programming language can be expressed as some Turing machine. I guess, that there exists universal algorithm for doing that (e.g. one can take the ...
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How do bottom up parser evaluate things that need an inherited attribute?

I learned that Bottom up parsers use only synthesized attributes to evaluate semantics. Which makes sense considering that it would be very hard to evaluate an inherited attribute in bottom up ...
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How does a compiler give an immediate compilation error?

I am confused. I know that compilers translate your code one time as a whole into intermediary code, but how come when I type in something improper, the IDE shoots out a compilation error immediately? ...
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LL(1) parsing table construction

i have the following CFG E -> ABC A-> a|Cb|epsilon B-> c|xA|epsilon C-> y|z and the First of the Non-Terminal : ...
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1answer
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How to view Graph Reduction/Graph Representation for a Haskell program?

I know that under the hood, for a Haskell program, the GHC compiler uses graph reduction for optimization. Is there any way to view this graphical representation of the program? I haven't been able to ...
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244 views

LR(1) parsing, problem with look ahead symbols

I understand the concept of LR(1) parsing and lookahead symbols. I have the solution to the exercise and it does not agree with my solution. I'm trying to fill the LR(1) parsing table for the grammar ...
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A state machine that is either DFA or NFA: is it possible?

I am studying Crafting Interpreters, and although I understand the responsibility of the Scanner (or Lexer), I still cannot understand if it is a deterministic finite automaton or non-deterministic ...
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BNF syntax for a recursive function?

I'm to write a syntax that will allow for a recursive function, i.e. f(x) = if x == 0 then x else f(x+1) Here's one attempt at creating the grammar: But I don't ...
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Can reading a value of a variable kill the definition of the variable?

I was going through the concept of reaching definitions from the red dragon book. The authors define reaching definitions as follows: Definition: We say a definition $d$ reaches a point $p$ if there ...
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SSA Copy Folding

When can we fold copies in SSA? We are clearly allowed to fold a copy such as a0 = call foo() b0 = a0 But what about a program such as ...
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133 views

Dynamic list for frame pointers and static list of nested activation frames

I am going through the book Compiler Construction by Niklaus Wirth. The following is what I feel to be stated summarily by his lesson on procedure calls: The compilation of a procedure call is the ...
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Eliminating ambiguity in $A \to AA \mid (A) \mid a$

I'm trying to solve this complier design problem related to ambiguity in CFG the given grammar is \begin{align} &A → AA \\ &A → (A) \\ &A → a \end{align} I was able to find that this ...
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Using saved registers at the main function with no other function calls [RISC-V]

The convention when a function is going to use a saved register is to save the contents of that register to the stack in case the caller (if there's one? the main function doesn't have one) had been ...
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Generating a recursive descent parser for grammar having Kleene star

From what I have been taught, I cannot use left-recursive, nondeterministic, or ambiguous grammars in recursive descent parsers. So, here is the grammar: \begin{align} &E \to E+T \mid T \\ &T \...
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What is a good general-knowledge-level title description of Dr. Aho's and Dr. Ullman's body of work for which they were awarded the 2020 Turing Award?

I recently read in the New York Times that my old "Data Structures and Algorithms" class professor Dr. Ullman had received the Turing Award along with Dr. Aho. The article title was "...
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How is $A.in$ an inherited attributed in $2nd$ production in $(1) S \rightarrow A_1A_2\{ A_1.in := 1; A_2.in := 2 \}(2) A\rightarrow a\{print(A.in)\}$

Below is an excerpt from the Red Dragon book. $$(1) \quad S \rightarrow A_1 \quad A_2 \quad\{ A_1.in : = 1;\quad A_2.in : = 2 ;\}$$ $$(2) \quad A \rightarrow a \quad \{ print(A.in) \}$$ We find that ...
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L-attributed definitions include all syntax-directed definitions based on LL(1) grammars

I was going through the text Compilers: Principles, Techniques and Tools by Ullman et. al where I came across the following claim: L-attributed definitions include all syntax-directed definitions ...
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In syntax-directed definition, terminals are assumed to have synthesized attributes only, definition doesn't provide any semantic rules for terminals?

I was going through the text Compilers: Principles,Techniques and Tools by Ullman et. al. where I came across the claim in the question by authors. Below is the definition and following it is the ...
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$\text{“The error entries in the goto table are never consulted”}$ - intuitive explanation of the above claim with respect to $LR$ parsing tables

I was going through the text : Compilers: Principles, Techniques and Tools by Ullman et. al where I came across a claim: $\text{"The error entries in the goto table are never consulted"}$ I feel ...
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Calculating worklist with live variable analysis

I am struggling with the calculation of the worklist algorithm, I do not want to implement the iterative algorithm as so many redundant steps it takes. The algorithm I am following to calculate the ...
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Is there a name for a compiler that runs once at runtime right before a program is executed?

I wrote a tiny compiler that is used to execute user-defined plugin code. The compiler is shipped as part of the application. When the user loads a plugin, the compiler runs first (once) and then the ...
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In shift reduce parsing why the handle always eventually appear on top of the stack and never inside?

I was going through the text Compilers: Principles, Techniques and Tools by Ullman et. al where I came across the excerpt where the authors try to justify why stack is the best data structure of shift ...

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