a27da05

[JSC] DFG strength reduction folds a compiler-thread RegExp execution failure into a definite no-match
https://bugs.webkit.org/show_bug.cgi?id=319452

Reviewed by NOBODY (OOPS!).

313689@main made RegExp bytecode compilation mutator-only: when Yarr JIT code returns
JITCodeFailure on a compiler thread and no bytecode exists, matchInline bails out with
-1 / MatchResult::failed().

That bail is indistinguishable from a real no-match. If a RegExp only ever runs via the
Yarr JIT (so bytecode is never compiled) and the JIT stack check fails against the small
compiler-thread stack, matchConcurrently reports an authoritative no-match and DFG
strength reduction permanently folds exec to null and test to false, even though the
mutator matches successfully.

This patch keeps the JITCodeFailure sentinel on the bail path and makes matchConcurrently
return false for it, so strength reduction gives up folding and defers to runtime.

    const re = new RegExp("^" + "a?".repeat(30000) + "$");
    function f() { return re.test("a"); }
    // After DFG tier-up, f() returns false forever; direct re.test("a") is true.

Test: JSTests/stress/dfg-strength-reduction-regexp-jit-code-failure-not-no-match.js

* JSTests/stress/dfg-strength-reduction-regexp-jit-code-failure-not-no-match.js: Added.
(foldableTest):
(foldableExec):
* Source/JavaScriptCore/runtime/RegExp.cpp:
(JSC::RegExp::matchConcurrently):
* Source/JavaScriptCore/runtime/RegExpInlines.h:
(JSC::RegExp::matchInline):

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