[clang] [llvm] [WebAssembly] Implement an alternative translation for -wasm-enable-sjlj (PR #84137)

[Heejin Ahn via cfe-commits]

================
@@ -129,27 +129,21 @@
 ///
 /// If there are calls to setjmp()
 ///
-/// 2) In the function entry that calls setjmp, initialize setjmpTable and
-///    sejmpTableSize as follows:
-///      setjmpTableSize = 4;
-///      setjmpTable = (int *) malloc(40);
-///      setjmpTable[0] = 0;
-///    setjmpTable and setjmpTableSize are used to call saveSetjmp() function in
-///    Emscripten compiler-rt.
+/// 2) In the function entry that calls setjmp, initialize
+///    functionInvocationId as follows:
+///
+///    functionInvocationId = alloca(4)
+///
+///    Note: the alloca size is not important as this pointer is
+///    merely used for pointer comparisions.
 ///
 /// 3) Lower
 ///      setjmp(env)
 ///    into
-///      setjmpTable = saveSetjmp(env, label, setjmpTable, setjmpTableSize);
-///      setjmpTableSize = getTempRet0();
-///    For each dynamic setjmp call, setjmpTable stores its ID (a number which
-///    is incrementally assigned from 0) and its label (a unique number that
-///    represents each callsite of setjmp). When we need more entries in
-///    setjmpTable, it is reallocated in saveSetjmp() in Emscripten's
-///    compiler-rt and it will return the new table address, and assign the new
-///    table size in setTempRet0(). saveSetjmp also stores the setjmp's ID into
-///    the buffer 'env'. A BB with setjmp is split into two after setjmp call in
-///    order to make the post-setjmp BB the possible destination of longjmp BB.
+///      __wasm_setjmp(env, label, functionInvocationId)
+///
+///    A BB with setjmp is split into two after setjmp call in order to
+///    make the post-setjmp BB the possible destination of longjmp BB.
----------------
aheejin wrote:

I think it's helpful to mention what `__wasm_setjmp` does: It saves `functionInvocationId` and `label` into `env`.

https://github.com/llvm/llvm-project/pull/84137