Changes between Version 14 and Version 15 of Commentary/Compiler/CmmType

Timestamp:

01/12/07 12:55:51 (6 years ago)

Author:

p_tanski

Comment:

cleanup; begin colour-code

Commentary/Compiler/CmmType

@@ -147 +147 @@
 Cmm modules contain static data elements (see [wiki:Commentary/Compiler/CmmType#LiteralsandLabels Literals and Labels]) and [wiki:Commentary/Compiler/CmmType#BasicBlocks:Procedures Basic Blocks], collected together in `Cmm`, a type synonym for `GenCmm`, defined in [[GhcFile(compiler/cmm/Cmm.hs)]]:
 {{{
-newtype GenCmm d i = Cmm [GenCmmTop d i]
- 
-type Cmm = GenCmm CmmStatic CmmStmt
-
-data GenCmmTop d i
-  = CmmProc
-     [d]               -- Info table, may be empty
-     CLabel            -- Used to generate both info & entry labels
-     [LocalReg]        -- Argument locals live on entry (C-- procedure params)
-     [GenBasicBlock i] -- Code, may be empty.  The first block is
-                       -- the entry point.  The order is otherwise initially 
-                       -- unimportant, but at some point the code gen will
-                       -- fix the order.
-
-                       -- the BlockId of the first block does not give rise
-                       -- to a label.  To jump to the first block in a Proc,
-                       -- use the appropriate CLabel.
-
-  -- some static data.
-  | CmmData Section [d] -- constant values only
-
-type CmmTop = GenCmmTop CmmStatic CmmStmt
+#!html
+<pre>
+<u><font color=Magenta>newtype</font></u> <font color=Green>GenCmm</font> <font color=Black>d</font> <font color=Black>i</font> <font color=Blue>=</font> <font color=Green>Cmm</font> <font color=Blue>[</font><font color=Green>GenCmmTop</font> <font color=Black>d</font> <font color=Black>i</font><font color=Blue>]</font>
+
+<u><font color=Magenta>type</font></u> <font color=Green>Cmm</font> <font color=Blue>=</font> <font color=Green>GenCmm</font> <font color=Green>CmmStatic</font> <font color=Green>CmmStmt</font>
+
+
+<u><font color=Magenta>data</font></u> <font color=Green>GenCmmTop</font> <font color=Black>d</font> <font color=Black>i</font>
+  <font color=Blue>=</font> <font color=Green>CmmProc</font>
+     <font color=Blue>[</font><font color=Black>d</font><font color=Blue>]</font>              <font color=Red>-- Info table, may be empty</font>
+     <font color=Green>CLabel</font>            <font color=Red>-- Used to generate both info &amp; entry labels</font>
+     <font color=Blue>[</font><font color=Green>LocalReg</font><font color=Blue>]</font>        <font color=Red>-- Argument locals live on entry (C-- procedure params)</font>
+     <font color=Blue>[</font><font color=Green>GenBasicBlock</font> <font color=Black>i</font><font color=Blue>]</font> <font color=Red>-- Code, may be empty.  The first block is</font>
+                       <font color=Red>-- the entry point.  The order is otherwise initially </font>
+                       <font color=Red>-- unimportant, but at some point the code gen will</font>
+                       <font color=Red>-- fix the order.</font>
+
+                       <font color=Red>-- the BlockId of the first block does not give rise</font>
+                       <font color=Red>-- to a label.  To jump to the first block in a Proc,</font>
+                       <font color=Red>-- use the appropriate CLabel.</font>
+
+  <font color=Red>-- some static data.</font>
+  <font color=Blue>|</font> <font color=Green>CmmData</font> <font color=Green>Section</font> <font color=Blue>[</font><font color=Black>d</font><font color=Blue>]</font>      <font color=Red>-- constant values only</font>
+
+<u><font color=Magenta>type</font></u> <font color=Green>CmmTop</font> <font color=Blue>=</font> <font color=Green>GenCmmTop</font> <font color=Green>CmmStatic</font> <font color=Green>CmmStmt</font>
+</pre>
 }}}
 `CmmStmt` is described in [wiki:Commentary/Compiler/CmmType#StatementsandCalls Statements and Calls];[[BR]]
@@ -179 +183 @@
 Cmm procedures are represented by the first constructor in `GenCmmTop d i`:
 {{{
-    CmmProc [d] CLabel [LocalReg] [GenBasicBlock i]
+#!html
+<pre>
+    <font color=Green>CmmProc</font> <font color=Blue>[</font><font color=Black>d</font><font color=Blue>]</font> <font color=Green>CLabel</font> <font color=Blue>[</font><font color=Green>LocalReg</font><font color=Blue>]</font> <font color=Blue>[</font><font color=Green>GenBasicBlock</font> <font color=Black>i</font><font color=Blue>]</font>
+</pre>
 }}}
 For a description of Cmm labels and the `CLabel` data type, see the subsection [wiki:Commentary/Compiler/CmmType#LiteralsandLabels Literals and Labels], below.
@@ -185 +192 @@
 Cmm Basic Blocks are labeled blocks of Cmm code ending in an explicit jump.  Sections (see [wiki:Commentary/Compiler/CmmType#SectionsandDirectives Sections and Directives]) have no jumps--in Cmm, Sections cannot contain nested Procedures (see, e.g., [wiki:Commentary/Compiler/CmmType#CompilingCmmwithGHC Compiling Cmm with GHC]).  Basic Blocks encapsulate parts of Procedures.  The data type `GenBasicBlock` and the type synonym `CmmBasicBlock` encapsulate Basic Blocks; they are defined in [[GhcFile(compiler/cmm/Cmm.hs)]]:
 {{{
-data GenBasicBlock i = BasicBlock BlockId [i]
-
-type CmmBasicBlock = GenBasicBlock CmmStmt
-
-newtype BlockId = BlockId Unique
-  deriving (Eq,Ord)
-
-instance Uniquable BlockId where
-  getUnique (BlockId u) = u
+#!html
+<pre>
+<u><font color=Magenta>data</font></u> <font color=Green>GenBasicBlock</font> <font color=Black>i</font> <font color=Blue>=</font> <font color=Green>BasicBlock</font> <font color=Green>BlockId</font> <font color=Blue>[</font><font color=Black>i</font><font color=Blue>]</font>
+
+<u><font color=Magenta>type</font></u> <font color=Green>CmmBasicBlock</font> <font color=Blue>=</font> <font color=Green>GenBasicBlock</font> <font color=Green>CmmStmt</font>
+
+<u><font color=Magenta>newtype</font></u> <font color=Green>BlockId</font> <font color=Blue>=</font> <font color=Green>BlockId</font> <font color=Green>Unique</font>
+  <u><font color=Magenta>deriving</font></u> <font color=Blue>(</font><font color=Green>Eq</font><font color=Blue>,</font><font color=Green>Ord</font><font color=Blue>)</font>
+
+<u><font color=Magenta>instance</font></u> <font color=Green>Uniquable</font> <font color=Green>BlockId</font> <u><font color=Magenta>where</font></u>
+  <font color=Orange>getUnique</font> <font color=Blue>(</font><font color=Green>BlockId</font> <font color=Black>u</font><font color=Blue>)</font> <font color=Blue>=</font> <font color=Black>u</font>
+</pre>
 }}}
 The `BlockId` data type simply carries a `Unique` with each Basic Block.  For descriptions of `Unique`, see 
@@ -205 +215 @@
 C-- and Cmm hide the actual number of registers available on a particular machine by assuming an "infinite" supply of registers.  A backend, such as the NCG or C compiler on GHC, will later optimise the number of registers used and assign the Cmm variables to actual machine registers; the NCG temporarily stores any overflow in a small memory stack called the ''spill stack'', while the C compiler relies on C's own runtime system.  Haskell handles Cmm registers with three data types: `LocalReg`, `GlobalReg` and `CmmReg`.  `LocalReg`s and `GlobalRegs` are collected together in a single `Cmm` data type:
 {{{
-data CmmReg 
-  = CmmLocal  LocalReg
-  | CmmGlobal GlobalReg
+#!html
+<pre>
+<u><font color=Magenta>data</font></u> <font color=Green>CmmReg</font> 
+  <font color=Blue>=</font> <font color=Green>CmmLocal</font>  <font color=Green>LocalReg</font>
+  <font color=Blue>|</font> <font color=Green>CmmGlobal</font> <font color=Green>GlobalReg</font>
+  <u><font color=Magenta>deriving</font></u><font color=Blue>(</font> <font color=Green>Eq</font> <font color=Blue>)</font>
+</pre>
 }}}
 
@@ -213 +227 @@
 Local Registers exist within the scope of a Procedure:
 {{{
-data LocalReg
-  = LocalReg !Unique MachRep
+#!html
+<pre>
+<u><font color=Magenta>data</font></u> <font color=Green>LocalReg</font>
+  <font color=Blue>=</font> <font color=Green>LocalReg</font> <font color=Blue>!</font><font color=Green>Unique</font> <font color=Green>MachRep</font>
+</pre>
 }}}
 For a list of references with information on `Unique`, see the [wiki:Commentary/Compiler/CmmType#BasicBlocksandProcedures Basic Blocks and Procedures] section, above.
@@ -220 +237 @@
 A `MachRep`, the type of a machine register, is defined in [[GhcFile(compiler/cmm/MachOp.hs)]]:
 {{{
-data MachRep
-  = I8          -- integral type, 8 bits wide (a byte)
-  | I16         -- integral type, 16 bits wide
-  | I32         -- integral type, 32 bits wide
-  | I64         -- integral type, 64 bits wide
-  | I128        -- integral type, 128 bits wide (an integral vector register)
-  | F32         -- floating point type, 32 bits wide (float)
-  | F64         -- floating point type, 64 bits wide (double)
-  | F80         -- extended double-precision, used in x86 native codegen only.
+#!html
+<pre>
+<u><font color=Magenta>data</font></u> <font color=Green>MachRep</font>
+  <font color=Blue>=</font> <font color=Green>I8</font>         <font color=Red>-- integral type, 8 bits wide (a byte)</font>
+  <font color=Blue>|</font> <font color=Green>I16</font>                <font color=Red>-- integral type, 16 bits wide</font>
+  <font color=Blue>|</font> <font color=Green>I32</font>                <font color=Red>-- integral type, 32 bits wide</font>
+  <font color=Blue>|</font> <font color=Green>I64</font>                <font color=Red>-- integral type, 64 bits wide</font>
+  <font color=Blue>|</font> <font color=Green>I128</font>       <font color=Red>-- integral type, 128 bits wide (an integral vector register)</font>
+  <font color=Blue>|</font> <font color=Green>F32</font>                <font color=Red>-- floating point type, 32 bits wide (float)</font>
+  <font color=Blue>|</font> <font color=Green>F64</font>                <font color=Red>-- floating point type, 64 bits wide (double)</font>
+  <font color=Blue>|</font> <font color=Green>F80</font>                <font color=Red>-- extended double-precision, used in x86 native codegen only.</font>
+  <u><font color=Magenta>deriving</font></u> <font color=Blue>(</font><font color=Green>Eq</font><font color=Blue>,</font> <font color=Green>Ord</font><font color=Blue>,</font> <font color=Green>Show</font><font color=Blue>)</font>
+</pre>
 }}}
 There is currently no register for floating point vectors, such as `F128`.  The types of Cmm variables are defined in the Happy parser file [[GhcFile(compiler/cmm/CmmParse.y)]] and the Alex lexer file [[GhcFile(compiler/cmm/CmmLex.x)]].  (Happy and Alex will compile these into `CmmParse.hs` and `CmmLex.hs`, respectively.)  Cmm recognises the following `C--` types as parseable tokens, listed next to their corresponding {{{define}}}s in [[GhcFile(includes/Cmm.h)]] and their STG types:
@@ -248 +269 @@
 These are universal both to a Cmm module and to the whole compiled program.  Variables are global if they are declared at the top-level of a compilation unit (outside any procedure).  Global Variables are marked as external symbols with the `.globl` assembler directive.  In Cmm, global registers are used for special STG registers and specific registers for passing arguments and returning values.  The Haskell representation of Global Variables (Registers) is the `GlobalReg` data type, defined in [[GhcFile(compiler/cmm/Cmm.hs)]]:
 {{{
-data GlobalReg
-  -- Argument and return registers
-  = VanillaReg                  -- general registers (int, pointer, char values)
-        {-# UNPACK #-} !Int     -- the register number, such as R3, R11
-  | FloatReg            -- single-precision floating-point registers
-        {-# UNPACK #-} !Int     -- register number
-  | DoubleReg           -- double-precision floating-point registers
-        {-# UNPACK #-} !Int     -- register number
-  | LongReg             -- long int registers (64-bit, really)
-        {-# UNPACK #-} !Int     -- register number
-  -- STG registers
-  | Sp                  -- Stack ptr; points to last occupied stack location.
-  | SpLim               -- Stack limit
-  | Hp                  -- Heap ptr; points to last occupied heap location.
-  | HpLim               -- Heap limit register
-  | CurrentTSO          -- pointer to current thread's TSO
-  | CurrentNursery      -- pointer to allocation area
-  | HpAlloc             -- allocation count for heap check failure
-
-                -- We keep the address of some commonly-called 
-                -- functions in the register table, to keep code
-                -- size down:
-  | GCEnter1            -- stg_gc_enter_1
-  | GCFun               -- stg_gc_fun
-
-  -- Base offset for the register table, used for accessing registers
-  -- which do not have real registers assigned to them.  This register
-  -- will only appear after we have expanded GlobalReg into memory accesses
-  -- (where necessary) in the native code generator.
-  | BaseReg
-
-  -- Base Register for PIC (position-independent code) calculations
-  -- Only used inside the native code generator. It's exact meaning differs
-  -- from platform to platform (see compiler/nativeGen/PositionIndependentCode.hs).
-  | PicBaseReg
+#!html
+<pre>
+<u><font color=Magenta>data</font></u> <font color=Green>GlobalReg</font>
+  <font color=Red>-- Argument and return registers</font>
+  <font color=Blue>=</font> <font color=Green>VanillaReg</font>                 <font color=Red>-- pointers, unboxed ints and chars</font>
+        <font color=Red>{-# UNPACK #-}</font> <font color=Green>!</font><font color=Green>Int</font>    <font color=Red>-- register number, such as R3, R11</font>
+
+  <font color=Blue>|</font> <font color=Green>FloatReg</font>           <font color=Red>-- single-precision floating-point registers</font>
+        <font color=Red>{-# UNPACK #-}</font> <font color=Green>!</font><font color=Green>Int</font>    <font color=Red>-- register number</font>
+
+  <font color=Blue>|</font> <font color=Green>DoubleReg</font>          <font color=Red>-- double-precision floating-point registers</font>
+        <font color=Red>{-# UNPACK #-}</font> <font color=Green>!</font><font color=Green>Int</font>    <font color=Red>-- register number</font>
+
+  <font color=Blue>|</font> <font color=Green>LongReg</font>            <font color=Red>-- long int registers (64-bit, really)</font>
+        <font color=Red>{-# UNPACK #-}</font> <font color=Green>!</font><font color=Green>Int</font>    <font color=Red>-- register number</font>
+
+  <font color=Red>-- STG registers</font>
+  <font color=Blue>|</font> <font color=Green>Sp</font>                 <font color=Red>-- Stack ptr; points to last occupied stack location.</font>
+  <font color=Blue>|</font> <font color=Green>SpLim</font>              <font color=Red>-- Stack limit</font>
+  <font color=Blue>|</font> <font color=Green>Hp</font>                 <font color=Red>-- Heap ptr; points to last occupied heap location.</font>
+  <font color=Blue>|</font> <font color=Green>HpLim</font>              <font color=Red>-- Heap limit register</font>
+  <font color=Blue>|</font> <font color=Green>CurrentTSO</font>         <font color=Red>-- pointer to current thread's TSO</font>
+  <font color=Blue>|</font> <font color=Green>CurrentNursery</font>     <font color=Red>-- pointer to allocation area</font>
+  <font color=Blue>|</font> <font color=Green>HpAlloc</font>            <font color=Red>-- allocation count for heap check failure</font>
+
+                <font color=Red>-- We keep the address of some commonly-called </font>
+                <font color=Red>-- functions in the register table, to keep code</font>
+                <font color=Red>-- size down:</font>
+  <font color=Blue>|</font> <font color=Green>GCEnter1</font>           <font color=Red>-- stg_gc_enter_1</font>
+  <font color=Blue>|</font> <font color=Green>GCFun</font>              <font color=Red>-- stg_gc_fun</font>
+
+  <font color=Red>-- Base offset for the register table, used for accessing registers</font>
+  <font color=Red>-- which do not have real registers assigned to them.  This register</font>
+  <font color=Red>-- will only appear after we have expanded GlobalReg into memory accesses</font>
+  <font color=Red>-- (where necessary) in the native code generator.</font>
+  <font color=Blue>|</font> <font color=Green>BaseReg</font>
+
+  <font color=Red>-- Base Register for PIC (position-independent code) calculations</font>
+  <font color=Red>-- Only used inside the native code generator. It's exact meaning differs</font>
+  <font color=Red>-- from platform to platform  (see compiler/nativeGen/PositionIndependentCode.hs).</font>
+  <font color=Blue>|</font> <font color=Green>PicBaseReg</font>
+</pre>
 }}}
 For a description of the `Hp` and `Sp` ''virtual registers'', see [wiki:Commentary/Rts/HaskellExecution The Haskell Execution Model] page.  General `GlobalReg`s are clearly visible in Cmm code according to the following syntax defined in [[GhcFile(compiler/cmm/CmmLex.x)]]:
@@ -310 +338 @@
 Hints are represented in Haskell as `MachHint`s, defined near `MachRep` in [[GhcFile(compiler/cmm/MachOp.hs)]]:
 {{{
-data MachHint
-  = NoHint      -- string: "NoHint"     Cmm syntax: [empty]     (C-- uses "")
-  | PtrHint     -- string: "PtrHint"    Cmm syntax: "ptr"       (C-- uses "address")
-  | SignedHint  -- string: "SignedHint" Cmm syntax: "signed"
-  | FloatHint   -- string: "FloatHint"  Cmm syntax: "float"
-}}}
+#!html
+<pre>
+<u><font color=Magenta>data</font></u> <font color=Green>MachHint</font>
+  <font color=Blue>=</font> <font color=Green>NoHint</font>     <font color=Red>-- string: "NoHint"     Cmm syntax: [empty]</font>
+  <font color=Blue>|</font> <font color=Green>PtrHint</font>    <font color=Red>-- string: "PtrHint"    Cmm syntax: "ptr"    (C-- uses "address")</font>
+  <font color=Blue>|</font> <font color=Green>SignedHint</font> <font color=Red>-- string: "SignedHint" Cmm syntax: "signed"</font>
+  <font color=Blue>|</font> <font color=Green>FloatHint</font>  <font color=Red>-- string: "FloatHint"  Cmm syntax: "float" </font>
+</pre>
+}}}
+
 Although the C-- specification does not allow the C-- type system to statically distinguish between floats, signed ints, unsigned ints or pointers, Cmm does. Cmm `MachRep`s carry the float or int kind of a variable, either within a local block or in a global register.  `GlobalReg` includes separate constructors for `Vanilla`, `Float`, `Double` and `Long`.  Cmm still does not distinguish between signed ints, unsigned ints and pointers (addresses) at the register level, as these are given ''hint'' pseudo-types or their real type is determined as they run through primitive operations.  `MachHint`s still follow the C-- specification and carry kind information as an aide to the backend optimisers.  
 
@@ -406 +438 @@
 Cmm literals are exactly like C-- literals, including the Haskell-style type syntax, for example: `0x00000001::bits32`.  Cmm literals may be used for initialisation by assignment or in expressions. The `CmmLit` and `CmmStatic` data types, defined in [[GhcFile(compiler/cmm/Cmm.hs)]] together represent Cmm literals, static information and Cmm labels:
 {{{
-data CmmLit
-  = CmmInt Integer  MachRep
-        -- Interpretation: the 2's complement representation of the value
-        -- is truncated to the specified size.  This is easier than trying
-        -- to keep the value within range, because we don't know whether
-        -- it will be used as a signed or unsigned value (the MachRep doesn't
-        -- distinguish between signed & unsigned).
-  | CmmFloat  Rational MachRep
-  | CmmLabel    CLabel                  -- Address of label
-  | CmmLabelOff CLabel Int              -- Address of label + byte offset
+#!html
+<pre>
+<u><font color=Magenta>data</font></u> <font color=Green>CmmLit</font>
+  <font color=Blue>=</font> <font color=Green>CmmInt</font> <font color=Green>Integer</font>  <font color=Green>MachRep</font>
+        <font color=Red>-- Interpretation: the 2's complement representation of the value</font>
+        <font color=Red>-- is truncated to the specified size.  This is easier than trying</font>
+        <font color=Red>-- to keep the value within range, because we don't know whether</font>
+        <font color=Red>-- it will be used as a signed or unsigned value (the MachRep doesn't</font>
+        <font color=Red>-- distinguish between signed &amp; unsigned).</font>
+  <font color=Blue>|</font> <font color=Green>CmmFloat</font>  <font color=Green>Rational</font> <font color=Green>MachRep</font>
+  <font color=Blue>|</font> <font color=Green>CmmLabel</font>    <font color=Green>CLabel</font>                        <font color=Red>-- Address of label</font>
+  <font color=Blue>|</font> <font color=Green>CmmLabelOff</font> <font color=Green>CLabel</font> <font color=Green>Int</font>           <font color=Red>-- Address of label + byte offset</font>
   
-        -- Due to limitations in the C backend, the following
-        -- MUST ONLY be used inside the info table indicated by label2
-        -- (label2 must be the info label), and label1 must be an
-        -- SRT, a slow entrypoint or a large bitmap (see the Mangler)
-        -- Don't use it at all unless tablesNextToCode.
-        -- It is also used inside the NCG when generating
-        -- position-independent code. 
-  | CmmLabelDiffOff CLabel CLabel Int   -- label1 - label2 + offset
+        <font color=Red>-- Due to limitations in the C backend, the following</font>
+        <font color=Red>-- MUST ONLY be used inside the info table indicated by label2</font>
+        <font color=Red>-- (label2 must be the info label), and label1 must be an</font>
+        <font color=Red>-- SRT, a slow entrypoint or a large bitmap (see the Mangler)</font>
+        <font color=Red>-- Don't use it at all unless tablesNextToCode.</font>
+        <font color=Red>-- It is also used inside the NCG during when generating</font>
+        <font color=Red>-- position-independent code. </font>
+  <font color=Blue>|</font> <font color=Green>CmmLabelDiffOff</font> <font color=Green>CLabel</font> <font color=Green>CLabel</font> <font color=Green>Int</font>   <font color=Red>-- label1 - label2 + offset</font>
+</pre>
 }}}
 Note how the `CmmLit` constructor `CmmInt Integer MachRep` contains sign information in the `Integer`, the representation of the literal itself: this conforms to the C-- specification, where integral literals contain sign information. For an example of a function using `CmmInt` sign information, see `cmmMachOpFold` in [[GhcFile(compiler/cmm/CmmOpt.hs)]], where sign-operations are performed on the `Integer`.
@@ -675 +710 @@
 
 ==== Quasi-operator Syntax ====
-If you read to the end of `expr` in [[GhcFile(compiler/cmm/CmmParse.y)]], you will notice that Cmm expressions also recognise a set of name (not symbol) based operators that would probably be better understood as ''quasi-operators'', listed in the next production rule: `expr0`.  The syntax for these quasi-operators is in some cases similar to syntax for Cmm statements and generally conform to the C-- specification, sections 3.3.2 (`expr`) and 7.4.1 (syntax of primitive operators), ''except that'' 3. ''and, by the equivalence of the two,'' 1. ''may return'' '''multiple''' '' arguments''. In Cmm, quasi-operators may have side effects. The syntax for quasi-operators may be:
+If you read to the end of `expr` in [[GhcFile(compiler/cmm/CmmParse.y)]], in the next production rule, `expr0`, you will notice that Cmm expressions also recognise a set of name (not symbol) based operators that would probably be better understood as ''quasi-operators''.  The syntax for these quasi-operators is in some cases similar to syntax for Cmm statements and generally conform to the C-- specification, sections 3.3.2 (`expr`) and 7.4.1 (syntax of primitive operators), ''except that'' 3. ''and, by the equivalence of the two,'' 1. ''may return'' '''multiple''' '' arguments''. In Cmm, quasi-operators may have side effects. The syntax for quasi-operators may be:
  1. `expr0` {{{`name`}}} `expr0`[[BR]](just like infix-functions in Haskell);
  1. `type[ expression ]`[[BR]](the memory access quasi-expression described in [wiki:Commentary/Compiler/CmmType#MemoryAccess Memory Access]; the Haskell representation of this syntax is `CmmLoad CmmExpr MachRep`); 
@@ -711 +746 @@
 Cmm Statements generally conform to the C-- specification, with a few exceptions noted below.  Cmm Statements implement:
  * no-op; the empty statement: `;`
- * C-- (C99/C++ style) comments: `// ... /n` and `/* ... */`
+ * C-- (C99/C++ style) comments: `// ... \n` and `/* ... */`
  * the assignment operator: `=`
  * store operation (assignment to a memory location): `type[expr] =`