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Diffstat (limited to 'chapter04')
| -rw-r--r-- | chapter04/README.md | 32 |
1 files changed, 17 insertions, 15 deletions
diff --git a/chapter04/README.md b/chapter04/README.md index fe338d0a..9c9b0b9d 100644 --- a/chapter04/README.md +++ b/chapter04/README.md @@ -85,15 +85,11 @@ Parser parser = new Parser("return arg; #showGraph;", TypeInteger.constant(2)); The graph:  - - The `arg` projection node is not included in the cluster(where `$ctrl` and `Start` are displayed)(0). - - `$ctrl` and `arg` are both defined in the outmost symbol table. - - Notice the extra symbol table created at index: 1(1). - - Notice how the dashed blue line is not drawn for `ctrl` and is not pointing to the `$ctrl node` in the cluster(2). + - The `arg` projection node is not included in the cluster(where `$ctrl` and `Start` are displayed).[^2] + - `$ctrl` and `arg` are both defined in the outermost symbol table, at lexical depth 0. + - There is an empty global-scope symbol table created at depth 1; in the future global variables will be defined here. + - There is no line for the scope `$ctrl`, because control is dead after the return. [^3] -`(0): ` Arg is a constant and gets stored in a constant node. -When `peephole` called, and compute is executed, the type returned is the type at the provided index in the TypeTuple. -It turns out - this returned type will be a `constant` TypeInteger with a `ProjNode`. -This can be replaced with a ConstantNode with the type passed in for `arg`. ```java public final Node peephole( ) { @@ -120,19 +116,16 @@ public final Node peephole( ) { return this; // won't get called ``` -`(1): ` We always create a symbol table when start parsing so that global symbols can be inserted. -We had to create explicitly a symbol table containing `CTRL` and `ARG` at index 0. The symbol table for global symbols is at index 1(nested and currently empty). -`(2): ` The control node is always set to null because there is no control after return. -It is manually set to null here: ``` ctrl(null); // Kill control ``` Which will call `setDef` to kill the node. If it does not exist we can't draw a line pointing to it. -#### arg is not provided: -Arg is not provided in this case: +#### Initial Argument Value +An argument is always provided, and defaults to `TypeInteger.BOT`. Individual tests can (and do) pass in other integer values. + ```java Parser parser = new Parser("return arg; #showGraph;", TypeInteger.BOT); ``` @@ -159,7 +152,10 @@ _is_con = false ``` We clearly see this is not a constant, so it can't get optimised out and will remain in the ProjNode cluster. -#### ctrl is not null: Next chapter(ch5) +#### When Is Control Not-Null? + +In later chapters, `$ctrl` will point to other control nodes, such as +`If` and `Region` (and `Loop`), but for now with now other control flow it always gets set to null after a `Return`. ## Changes to Type System @@ -373,3 +369,9 @@ By adding a bogus user we prevent it being mistaken for dead and being killed. [^1]: Click, C. (1995). Combining Analyses, Combining Optimizations, 131. + +[^2]: Arg is a constant valued, and is computed via a constant node. Arg is originally defined by ProjNode; when peephole is called, the computed type is a constant TypeInteger. +The ProjNode is replaced with a ConstantNode with the constant type. + +[^3]: The control node is always set to null because there is no control after return. +It is manually set to null here:
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