271a7bb144
Add a new index page to be the Flang documentation mainpage instead of Overview.md, which jumps straight into the compiler Design. The index file needs to be in .rst format to use the toctree directive to create table of contents. Also use the sphinx_markdown_tables extension to generate html tables form markdown. A number of additional style changes to the existing docs were needed to make this work well: * Convert all headings to the # style, which works better with toctree's titlesonly option. Ensure that there is only one top-level heading per document. * Add a title to documents that don't have one for rendering on the index. * Convert the grammar docs from .txt to .md. for better rendering * Fixed broken link to a section in another document - sphinx does not seem to support anchor links in markdown files. Depends on D87226 Reviewed By: sameeranjoshi Differential Revision: https://reviews.llvm.org/D87242
3.6 KiB
Bijective Internal Name Uniquing
.. contents::
:local:
FIR has a flat namespace. No two objects may have the same name at the module level. (These would be functions, globals, etc.) This necessitates some sort of encoding scheme to unique symbols from the front-end into FIR.
Another requirement is to be able to reverse these unique names and recover the associated symbol in the symbol table.
Fortran is case insensitive, which allows the compiler to convert the user's identifiers to all lower case. Such a universal conversion implies that all upper case letters are available for use in uniquing.
Prefix _Q
All uniqued names have the prefix sequence _Q to indicate the name has
been uniqued. (Q is chosen because it is a
low frequency letter
in English.)
Scope Building
Symbols can be scoped by the module, submodule, or procedure that contains
that symbol. After the _Q sigil, names are constructed from outermost to
innermost scope as
- Module name prefixed with
M - Submodule name prefixed with
S - Procedure name prefixed with
F
Given:
submodule (mod:s1mod) s2mod
...
subroutine sub
...
contains
function fun
The uniqued name of fun becomes:
_QMmodSs1modSs2modFsubPfun
Common blocks
- A common block name will be prefixed with
B
Given:
common /variables/ i, j
The uniqued name of variables becomes:
_QBvariables
Given:
common i, j
The uniqued name in case of blank common block becomes:
_QB
Module scope global data
- A global data entity is prefixed with
E - A global entity that is constant (parameter) will be prefixed with
EC
Given:
module mod
integer :: intvar
real, parameter :: pi = 3.14
end module
The uniqued name of intvar becomes:
_QMmodEintvar
The uniqued name of pi becomes:
_QMmodECpi
Procedures/Subprograms
- A procedure/subprogram is prefixed with
P
Given:
subroutine sub
The uniqued name of sub becomes:
_QPsub
Derived types and related
- A derived type is prefixed with
T - If a derived type has KIND parameters, they are listed in a consistent
canonical order where each takes the form
Kiand where i is the compile-time constant value. (All type parameters are integer.) If i is a negative value, the prefixKNwill be used and i will reflect the magnitude of the value.
Given:
module mymodule
type mytype
integer :: member
end type
...
The uniqued name of mytype becomes:
_QMmymoduleTmytype
Given:
type yourtype(k1,k2)
integer, kind :: k1, k2
real :: mem1
complex :: mem2
end type
The uniqued name of yourtype where k1=4 and k2=-6 (at compile-time):
_QTyourtypeK4KN6
- A derived type dispatch table is prefixed with
D. The dispatch table fortype twould be_QDTt - A type descriptor instance is prefixed with
C. Intrinsic types can be encoded with their names and kinds. The type descriptor for the typeyourtypeabove would be_QCTyourtypeK4KN6. The type descriptor forREAL(4)would be_QCrealK4.
Compiler generated names
Compiler generated names do not have to be mapped back to Fortran. These
names will be prefixed with _QQ and followed by a unique compiler
generated identifier. There is, of course, no mapping back to a symbol
derived from the input source in this case as no such symbol exists.