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Diffstat (limited to 'doc/il.txt')
| -rw-r--r-- | doc/il.txt | 46 |
1 files changed, 24 insertions, 22 deletions
diff --git a/doc/il.txt b/doc/il.txt index 964c864..14bd0c8 100644 --- a/doc/il.txt +++ b/doc/il.txt @@ -82,7 +82,7 @@ are listed below. * `[ ... ]` marks some syntax as optional; * `( ... ),` designates a comma-separated list of the enclosed syntax; - * `...*` and `...+` as used for arbitrary and + * `...*` and `...+` are used for arbitrary and at-least-once repetition. ~ Sigils @@ -114,13 +114,13 @@ starting with the sigil `?`. The IL makes very minimal use of types. By design, the types used are restricted to what is necessary for unambiguous compilation to machine code and C interfacing. Unlike LLVM, -QBE is not using types as a mean to safety, they are only -here for semantics purposes. +QBE is not using types as a means to safety; they are only +here for semantic purposes. The four base types are `w` (word), `l` (long), `s` (single), -and `d` (double), they stand respectively for 32 bits and -64 bits integers, and 32 bits and 64 bits floating points. -There are no pointer types available, pointers are typed +and `d` (double), they stand respectively for 32-bit and +64-bit integers, and 32-bit and 64-bit floating-point numbers. +There are no pointer types available; pointers are typed by an integer type sufficiently wide to represent all memory addresses (e.g. `l` on x64). Temporaries in the IL can only have a basic type. @@ -138,8 +138,8 @@ section. ~~~~~~~~~~~ The IL has a minimal subtyping feature for integer types. -Any value of type `l` can be used in a `w` context. When that -happens only the 32 least significant bits of the word value +Any value of type `l` can be used in a `w` context. In that +case, only the 32 least significant bits of the word value are used. Make note that it is the inverse of the usual subtyping on @@ -165,21 +165,21 @@ that they can be used directly in instructions; there is no need for a "load constant" instruction. The representation of integers is two's complement. -Floating point numbers are represented using the +Floating-point numbers are represented using the single-precision and double-precision formats of the -EEE 754 standard. +IEEE 754 standard. -Consants specify a sequence of bits and are untyped. -They are always parsed as 64 bits blobs. Depending on -the context surrounding one constant, only some of its +Constants specify a sequence of bits and are untyped. +They are always parsed as 64-bit blobs. Depending on +the context surrounding a constant, only some of its bits are used. For example, in the program below, the -two variables defined have the same value since the fist +two variables defined have the same value since the first operand of the substraction is a word (32 bits) context. %x =w sub -1, 0 %y =w sub 4294967295, 0 -Because specifying floating point constants by their bits +Because specifying floating-point constants by their bits makes the code less readable, syntactic sugar is provided to express them. Standard scientific notation is used with a prefix of `s_` for single and `d_` for double-precision @@ -189,8 +189,8 @@ the same double-precision constant. %x =d add d_0, d_-1 %y =d add d_0, -4616189618054758400 -Global symbols can also be used directly as constants, -they will be resolved and turned to actual numeric +Global symbols can also be used directly as constants; +they will be resolved and turned into actual numeric constants by the linker. - 4. Definitions @@ -218,26 +218,28 @@ using the `export` keyword. 'type' :IDENT '=' 'align' NUMBER '{' NUMBER '}' Aggregate type definitions start with the `type` keyword. -They have file scope but types must be defined before their +They have file scope, but types must be defined before their first use. The inner structure of a type is expressed by a -comma separated list of <@ Simple Types> enclosed in curly +comma-separated list of <@ Simple Types> enclosed in curly braces. type :fourfloats = { s, s, d, d } For ease of generation, a trailing comma is tolerated by the parser. In case many items of the same type are -sequenced (like in a C array), the sorter array syntax +sequenced (like in a C array), the shorter array syntax can be used. type :abyteandmanywords = { b, w 100 } By default, the alignment of an aggregate type is the maximum alignment of its members. The alignment can be -explicitely specified by the programmer +explicitly specified by the programmer. + + type :cryptovector = align 16 { w 4 } Opaque types are used when the inner structure of an -aggregate cannot be specified, the alignment for opaque +aggregate cannot be specified; the alignment for opaque types is mandatory. They are defined by simply enclosing their size between curly braces. |