gccint: GENERIC

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1 11 GENERIC
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1 The purpose of GENERIC is simply to provide a language-independent way
1 of representing an entire function in trees.  To this end, it was
1 necessary to add a few new tree codes to the back end, but almost
1 everything was already there.  If you can express it with the codes in
1 'gcc/tree.def', it's GENERIC.
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1  Early on, there was a great deal of debate about how to think about
1 statements in a tree IL.  In GENERIC, a statement is defined as any
1 expression whose value, if any, is ignored.  A statement will always
1 have 'TREE_SIDE_EFFECTS' set (or it will be discarded), but a
1 non-statement expression may also have side effects.  A 'CALL_EXPR', for
1 instance.
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1  It would be possible for some local optimizations to work on the
1 GENERIC form of a function; indeed, the adapted tree inliner works fine
1 on GENERIC, but the current compiler performs inlining after lowering to
1 GIMPLE (a restricted form described in the next section).  Indeed,
1 currently the frontends perform this lowering before handing off to
1 'tree_rest_of_compilation', but this seems inelegant.
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· Deficiencies                Topics net yet covered in this document.
· Tree overview               All about 'tree's.
· Types                       Fundamental and aggregate types.
· Declarations                Type declarations and variables.
· Attributes                  Declaration and type attributes.
· Expressions Expression trees.            Operating on data.
· Statements                  Control flow and related trees.
· Functions                   Function bodies, linkage, and other aspects.
· Language-dependent trees    Topics and trees specific to language front ends.
· C and C++ Trees             Trees specific to C and C++.
· Java Trees                  Trees specific to Java.
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