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[TableGen] Use less stack in DAGISelMatcherOpt

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Refactor a helper function, FactorNodes, to search for a push node in constant space. This resolves a problem in a not-yet-upstreamed backend where a recursive pattern blew the call stack (at a depth of 255) under a debug build of tablegen. No functional change so no new test coverage. The change is minimal to avoid disturbing existing behaviour.

Differential Revision: https://reviews.llvm.org/D29080

llvm-svn: 294230
This commit is contained in:
Jon Chesterfield 2017-02-06 19:41:44 +00:00
parent 8b0a9dd9e7
commit b7704a045e
1 changed files with 15 additions and 9 deletions
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24
utils/TableGen/DAGISelMatcherOpt.cpp
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@ -181,15 +181,21 @@ static Matcher *FindNodeWithKind(Matcher *M, Matcher::KindTy Kind) {
/// ABC
/// XYZ
///
static void FactorNodes(std::unique_ptr<Matcher> &MatcherPtr) {
// If we reached the end of the chain, we're done.
Matcher *N = MatcherPtr.get();
if (!N) return;
// If this is not a push node, just scan for one.
ScopeMatcher *Scope = dyn_cast<ScopeMatcher>(N);
if (!Scope)
return FactorNodes(N->getNextPtr());
static void FactorNodes(std::unique_ptr<Matcher> &InputMatcherPtr) {
// Look for a push node. Iterates instead of recurses to reduce stack usage.
ScopeMatcher *Scope = nullptr;
std::unique_ptr<Matcher> *RebindableMatcherPtr = &InputMatcherPtr;
while (!Scope) {
// If we reached the end of the chain, we're done.
Matcher *N = RebindableMatcherPtr->get();
if (!N) return;
// If this is not a push node, just scan for one.
Scope = dyn_cast<ScopeMatcher>(N);
if (!Scope)
RebindableMatcherPtr = &(N->getNextPtr());
}
std::unique_ptr<Matcher> &MatcherPtr = *RebindableMatcherPtr;
// Okay, pull together the children of the scope node into a vector so we can
// inspect it more easily.