[PATCH] D44134: [WebAssembly] Add WebAssemblyException information analysis

[David Majnemer via Phabricator via llvm-commits]

majnemer added inline comments.


================
Comment at: lib/Target/WebAssembly/WebAssemblyExceptionInfo.cpp:25-26
+/// Because CFGSort requires all the BBs within a catch part to be sorted
+/// together as it does for loops, this pass calculates the nesting structure of
+/// catch part of exceptions in a function.
+///
----------------
aheejin wrote:
> majnemer wrote:
> > aheejin wrote:
> > > majnemer wrote:
> > > > What happens if some BBs belong to two different catch blocks?
> > > Like loop nesting structure, catch block structure should form a nested structure, so a BB belongs to both catch1 and catch2, catch1 should contain catch2 or vice versa.
> > This is not so in LLVM IR. For example:
> > 
> > 
> > ```
> > define dso_local void @f() local_unnamed_addr #0 personality i8* bitcast (i32 (...)* @__gxx_personality_v0 to i8*) {
> >   invoke void @x0()
> >           to label %5 unwind label %1
> > 
> > ; <label>:1:                                      ; preds = %0
> >   %2 = landingpad { i8*, i32 }
> >           catch i8* null
> >   %3 = extractvalue { i8*, i32 } %2, 0
> >   %4 = tail call i8* @__cxa_begin_catch(i8* %3) #3
> >   br label %11
> > 
> > ; <label>:5:                                      ; preds = %0
> >   invoke void @x1()
> >           to label %10 unwind label %6
> > 
> > ; <label>:6:                                      ; preds = %5
> >   %7 = landingpad { i8*, i32 }
> >           catch i8* null
> >   %8 = extractvalue { i8*, i32 } %7, 0
> >   %9 = tail call i8* @__cxa_begin_catch(i8* %8) #3
> >   br label %11
> > 
> > ; <label>:10:                                     ; preds = %5
> >   ret void
> > 
> > ; <label>:11:                                     ; preds = %6, %1
> >   tail call void @abort() #4
> >   unreachable
> > }
> > 
> > declare dso_local void @x0() local_unnamed_addr #1
> > 
> > declare i32 @__gxx_personality_v0(...)
> > 
> > declare i8* @__cxa_begin_catch(i8*) local_unnamed_addr
> > 
> > declare dso_local void @x1() local_unnamed_addr #1
> > 
> > ; Function Attrs: noreturn nounwind
> > declare dso_local void @abort() local_unnamed_addr #2
> > ```
> > 
> > In this example, BB#11 belongs to two different catch blocks.
> ```
> An exception catch part is defined as a BB with catch instruction and all other BBs dominated by this BB.
> ```
> 
> In this case BB#11 is neither in the two catch blocks. Catch#1 contains BB#6 and BB#11, and Catch#2 contains BB#2 only.
Why doesn't Catch#2 contain BB#11? The two catches are identical, they just jump to a shared common block after executing __cxa_begin_catch.


Repository:
  rL LLVM

https://reviews.llvm.org/D44134