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There are three kinds of "rethrowing" BBs in this pass: 1. In Emscripten SjLj, after a possibly longjmping function call, we check if the thrown longjmp corresponds to one of setjmps within the current function. If not, we rethrow the longjmp by calling `emscripten_longjmp`. 2. In Emscripten EH, after a possibly throwing function call, we check if the thrown exception corresponds to the current `catch` clauses. If not, we rethrow the exception by calling `__resumeException`. 3. When both Emscripten EH and SjLj are used, when we check for an exception after a possibly throwing function call, it is possible that we get not an exception but a longjmp. In this case, we shouldn't swallow it; we should rethrow the longjmp by calling `emscripten_longjmp`. 4. When both Emscripten EH and SjLj are used, when we check for a longjmp after a possibly longjmping function call, it is possible that we get not a longjmp but an exception. In this case, we shouldn't swallot it; we should rethrow the exception by calling `__resumeException`. Case 1 is in Emscripten SjLj, 2 is in Emscripten EH, and 3 and 4 are relevant when both Emscripten EH and SjLj are used. 3 and 4 were first implemented in D106525. We create BBs for 1, 3, and 4 in this pass. We create those BBs for every throwing/longjmping function call, along with other BBs that contain condition checks. What this CL does is to create a single BB within a function for each of 1, 3, and 4 cases. These BBs are exiting BBs in the function and thus don't have successors, so easy to be shared between calls. The names of BBs created are: Case 1: `call.em.longjmp` Case 3: `rethrow.exn` Case 4: `rethrow.longjmp` For the case 2 we don't currently create BBs; we only replace the existing `resume` instruction with `call @__resumeException`. And Clang already creates only a single `resume` BB per function and reuses it, so we don't need to optimize this case. Not sure what are good benchmarks for EH/SjLj, but this decreases the size of the object file for `grfmt_jpeg.bc` (presumably from opencv) we got from one of our users by 8.9%. Even after running `wasm-opt -O4` on them, there is still 4.8% improvement. Reviewed By: dschuff Differential Revision: https://reviews.llvm.org/D108945
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9.0 KiB