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improved AST optimizer's analysis of variable usage in inlined functions

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This commit is contained in:
Vern Paxson 2023-12-04 16:50:59 -08:00
parent 087eb1ca4e
commit d0eb40ac92
2 changed files with 43 additions and 4 deletions
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40
src/script_opt/GenIDDefs.cc
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@ -62,7 +62,45 @@ TraversalCode GenIDDefs::PreStmt(const Stmt* s) {
auto block = cr->Block();
cr_active.push_back(confluence_blocks.size());
block->Traverse(this);
// Confluence for the bodies of catch-return's is a bit complex.
// We would like any expressions computed at the outermost level
// of the body to be available for script optimization *outside*
// the catch-return; this in particular is helpful in optimizing
// coalesced event handlers, but has other benefits as well.
//
// However, if one of the outermost statements executes a "return",
// then any outermost expressions computed after it might not
// be available. Put another way, the potentially-returning
// statement starts a confluence region that runs through the end
// of the body.
//
// To deal with this, we start off without a new confluence block,
// but create one upon encountering a statement that could return.
bool did_confluence = false;
if ( block->Tag() == STMT_LIST ) {
auto prev_stmt = s;
auto& stmts = block->AsStmtList()->Stmts();
for ( auto& st : stmts ) {
if ( ! did_confluence && st->CouldReturn(false) ) {
StartConfluenceBlock(prev_stmt);
did_confluence = true;
}
st->Traverse(this);
}
}
else
// If there's just a single statement then there are no
// expressions computed subsequent to it that we need to
// worry about, so just do ordinary traversal.
block->Traverse(this);
if ( did_confluence )
EndConfluenceBlock();
cr_active.pop_back();
auto retvar = cr->RetVar();

7
src/script_opt/GenIDDefs.h
View file

@ -93,9 +93,10 @@ private:
// Stack of confluence blocks corresponding to activate catch-return
// statements. We used to stop identifier definitions at these
// boundaries, but given there's no confluence (i.e., the body of the
// catch-return *will* execute), we can do broader optimization if we
// don't treat them as their own (new) confluence blocks.
// boundaries, but given there's limited confluence (i.e., the body of
// the catch-return *will* execute, up through its first return), we
// can do broader optimization if we don't treat them as their own
// (new) confluence blocks.
std::vector<zeek_uint_t> cr_active;
// The following is parallel to confluence_blocks except