108580 2013-01-31 22:01:37 -0800 DFG::CFGSimplificationPhase::keepOperandAlive() conflates liveness and availability 2013-01-31 23:43:28 -0800 1 1 1 Unclassified WebKit JavaScriptCore 528+ (Nightly build) All All RESOLVED FIXED P2 Normal --- 1 fpizlo fpizlo barraclough ggaren mark.lam mhahnenberg msaboff oliver sam oldest_to_newest 822320 0 fpizlo 2013-01-31 22:01:37 -0800 This is a harmless bug in that it only results in us keeping a bit too many things for OSR. But it's worth fixing so that the code is consistent. keepOperandAlive() is called when block A has a branch to blocks B and C, but the A->B edge is proven to never be taken and we want to optimize the code to have A unconditionally jump to C. In that case, for the purposes of OSR, we need to preserve the knowledge that the state that B expected to be live incoming from A ought still to be live up to the point of where the A->B,C branch used to be. The way we keep things alive is by using the variablesAtTail of A (i.e., we use the knowledge of in what manner A made state available to B and C). The way we choose which state should be kept alive ought to be chosen by the variablesAtHead of B (i.e. the things B says it needs from its predecessors, including A), except that keepOperandAlive() was previously just using variablesAtTail of A for this purpose. 822321 1 185943 fpizlo 2013-01-31 22:04:35 -0800 Created attachment 185943 the patch 822390 2 fpizlo 2013-01-31 23:43:28 -0800 Landed in http://trac.webkit.org/changeset/141544 185943 2013-01-31 22:04:35 -0800 2013-01-31 23:37:19 -0800 the patch blah.patch text/plain 5613 fpizlo SW5kZXg6IFNvdXJjZS9KYXZhU2NyaXB0Q29yZS9DaGFuZ2VMb2cKPT09PT09PT09PT09PT09PT09 PT09PT09PT09PT09PT09PT09PT09PT09PT09PT09PT09PT09PT09PT09PT09PT09PQotLS0gU291 cmNlL0phdmFTY3JpcHRDb3JlL0NoYW5nZUxvZwkocmV2aXNpb24gMTQxNTM2KQorKysgU291cmNl L0phdmFTY3JpcHRDb3JlL0NoYW5nZUxvZwkod29ya2luZyBjb3B5KQpAQCAtMSwzICsxLDM5IEBA CisyMDEzLTAxLTMxICBGaWxpcCBQaXpsbyAgPGZwaXpsb0BhcHBsZS5jb20+CisKKyAgICAgICAg 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