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

[Heejin Ahn via Phabricator via llvm-commits]

aheejin 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.
+///
----------------
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.


Repository:
  rL LLVM

https://reviews.llvm.org/D44134