[WebAssembly] Fix JS code mentions in LowerEmscriptenEHSjLj

[aheejin]

Summary

• Removes the mention of fastcomp, which is deprecated.
• Some functions in Emscripten have moved from JS glue code to compiler-rt/emscripten_setjmp.c and compiler-rt/emscripten_exception_builtins.c. This fixes comments about that.

[aheejin]

Revert accidental test changes

[aheejin]

Revert another accidental change

[aheejin]

Fix more comments

[aheejin]

Ping

[sbc100]

emitEndOfAsmFile

[aheejin]

In D101812#2740599, @sbc100 wrote:

emitEndOfAsmFile

What does this mean?

[sbc100]

In D101812#2740719, @aheejin wrote:

In D101812#2740599, @sbc100 wrote:

emitEndOfAsmFile

What does this mean?

Sorry my mouse button slipped and I pasted my cut buffer :)

llvm/lib/Target/WebAssembly/WebAssemblyLowerEmscriptenEHSjLj.cpp

 //=== WebAssemblyLowerEmscriptenEHSjLj.cpp - Lower exceptions for Emscripten =//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 ///
 /// \file
 /// This file lowers exception-related instructions and setjmp/longjmp
 /// function calls in order to use Emscripten's JavaScript try and catch
 /// mechanism.
 ///
 /// To handle exceptions and setjmp/longjmps, this scheme relies on JavaScript's
 /// try and catch syntax and relevant exception-related libraries implemented
-/// in JavaScript glue code that will be produced by Emscripten. This is similar
-/// to the current Emscripten asm.js exception handling in fastcomp. For
-/// fastcomp's EH / SjLj scheme, see these files in fastcomp LLVM branch:
-/// (Location: https://github.com/kripken/emscripten-fastcomp)
-/// lib/Target/JSBackend/NaCl/LowerEmExceptionsPass.cpp
-/// lib/Target/JSBackend/NaCl/LowerEmSetjmp.cpp
-/// lib/Target/JSBackend/JSBackend.cpp
-/// lib/Target/JSBackend/CallHandlers.h
+/// in JavaScript glue code that will be produced by Emscripten.
 ///
 /// * Exception handling
 /// This pass lowers invokes and landingpads into library functions in JS glue
 /// code. Invokes are lowered into function wrappers called invoke wrappers that
 /// exist in JS side, which wraps the original function call with JS try-catch.
 /// If an exception occurred, cxa_throw() function in JS side sets some
 /// variables (see below) so we can check whether an exception occurred from
 /// wasm code and handle it appropriately.

 /// we don't expect any exception-related instructions when SjLj runs.
 /// FIXME Currently this scheme does not support indirect call of setjmp,
 /// because of the limitation of the scheme itself. fastcomp does not support it
 /// either.
 ///
 /// In detail, this pass does following things:
 ///
 /// 1) Assumes the existence of global variables: __THREW__, __threwValue
-///    __THREW__ and __threwValue will be set in invoke wrappers
-///    in JS glue code. For what invoke wrappers are, refer to 3). These
-///    variables are used for both exceptions and setjmp/longjmps.
+///    __THREW__ and __threwValue are defined in compiler-rt in Emscripten.
+///    These variables are used for both exceptions and setjmp/longjmps.
 ///    __THREW__ indicates whether an exception or a longjmp occurred or not. 0
 ///    means nothing occurred, 1 means an exception occurred, and other numbers
 ///    mean a longjmp occurred. In the case of longjmp, __threwValue variable
 ///    indicates the corresponding setjmp buffer the longjmp corresponds to.
 ///
 /// * Exception handling
 ///
 /// 2) We assume the existence of setThrew and setTempRet0/getTempRet0 functions
-///    at link time.
-///    The global variables in 1) will exist in wasm address space,
-///    but their values should be set in JS code, so these functions
-///    as interfaces to JS glue code. These functions are equivalent to the
-///    following JS functions, which actually exist in asm.js version of JS
-///    library.
+///    at link time. setThrew exists in Emscripten's compiler-rt:
 ///
-///    function setThrew(threw, value) {
+///    void setThrew(int threw, int value) {
 ///      if (__THREW__ == 0) {
 ///        __THREW__ = threw;
 ///        __threwValue = value;
 ///      }
 ///    }
 //
 ///    setTempRet0 is called from __cxa_find_matching_catch() in JS glue code.
-///
 ///    In exception handling, getTempRet0 indicates the type of an exception
 ///    caught, and in setjmp/longjmp, it means the second argument to longjmp
 ///    function.
 ///
 /// 3) Lower
 ///      invoke @func(arg1, arg2) to label %invoke.cont unwind label %lpad
 ///    into
 ///      __THREW__ = 0;

 ///    wrappers we use JS try-catch to generate actual exception effects. It
 ///    also calls the original callee function. An example wrapper in JS code
 ///    would look like this:
 ///      function invoke_vi(index,a1) {
 ///        try {
 ///          Module["dynCall_vi"](index,a1); // This calls original callee
 ///        } catch(e) {
 ///          if (typeof e !== 'number' && e !== 'longjmp') throw e;
-///          asm["setThrew"](1, 0); // setThrew is called here
+///          _setThrew(1, 0); // setThrew is called here
 ///        }
 ///      }
 ///    If an exception is thrown, __THREW__ will be set to true in a wrapper,
 ///    so we can jump to the right BB based on this value.
 ///
 /// 4) Lower
 ///      %val = landingpad catch c1 catch c2 catch c3 ...
 ///      ... use %val ...

 ///
 /// In case calls to setjmp() exists
 ///
 /// 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 in saveSetjmp() function in JS
-///    code.
+///    setjmpTable and setjmpTableSize are used to call saveSetjmp() function in
+///    Emscripten compiler-rt.
 ///
 /// 3) Lower
 ///      setjmp(buf)
 ///    into
 ///      setjmpTable = saveSetjmp(buf, 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 JS code 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
-///    buf. 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.
+///    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 buf. 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.
 ///
 ///
 /// 4) Lower every call that might longjmp into
 ///      __THREW__ = 0;
 ///      call @__invoke_SIG(func, arg1, arg2)
 ///      %__THREW__.val = __THREW__;
 ///      __THREW__ = 0;
 ///      if (%__THREW__.val != 0 & __threwValue != 0) {
if (isa<InlineAsm>(Callee))
     return false;
   StringRef CalleeName = Callee->getName();
 
   // The reason we include malloc/free here is to exclude the malloc/free
   // calls generated in setjmp prep / cleanup routines.
   if (CalleeName == "setjmp" || CalleeName == "malloc" || CalleeName == "free")
     return false;
 
-  // There are functions in JS glue code
+  // There are functions in Emscripten's JS glue code or compiler-rt
   if (CalleeName == "__resumeException" || CalleeName == "llvm_eh_typeid_for" ||
       CalleeName == "saveSetjmp" || CalleeName == "testSetjmp" ||
       CalleeName == "getTempRet0" || CalleeName == "setTempRet0")
     return false;
 
   // __cxa_find_matching_catch_N functions cannot longjmp
   if (Callee->getName().startswith("__cxa_find_matching_catch_"))
     return false;