[WebAssembly] Exception handling: Switch to the new proposal

Summary:
This switches the EH implementation to the new proposal:
https://github.com/WebAssembly/exception-handling/blob/master/proposals/Exceptions.md
(The previous proposal was
 https://github.com/WebAssembly/exception-handling/blob/master/proposals/old/Exceptions.md)

- Instruction changes
  - Now we have one single `catch` instruction that returns a except_ref
    value
  - `throw` now can take variable number of operations
  - `rethrow` does not have 'depth' argument anymore
  - `br_on_exn` queries an except_ref to see if it matches the tag and
    branches to the given label if true.
  - `extract_exception` is a pseudo instruction that simulates popping
    values from wasm stack. This is to make `br_on_exn`, a very special
    instruction, work: `br_on_exn` puts values onto the stack only if it
    is taken, and the # of values can vay depending on the tag.

- Now there's only one `catch` per `try`, this patch removes all special
  handling for terminate pad with a call to `__clang_call_terminate`.
  Before it was the only case there are two catch clauses (a normal
  `catch` and `catch_all` per `try`).

- Make `rethrow` act as a terminator like `throw`. This splits BB after
  `rethrow` in WasmEHPrepare, and deletes an unnecessary `unreachable`
  after `rethrow` in LateEHPrepare.

- Now we stop at all catchpads (because we add wasm `catch` instruction
  that catches all exceptions), this creates new
  `findWasmUnwindDestinations` function in SelectionDAGBuilder.

- Now we use `br_on_exn` instrution to figure out if an except_ref
  matches the current tag or not, LateEHPrepare generates this sequence
  for catch pads:
```
  catch
  block i32
  br_on_exn $__cpp_exception
  end_block
  extract_exception
```

- Branch analysis for `br_on_exn` in WebAssemblyInstrInfo

- Other various misc. changes to switch to the new proposal.

Reviewers: dschuff

Subscribers: sbc100, jgravelle-google, sunfish, llvm-commits

Differential Revision: https://reviews.llvm.org/D57134

llvm-svn: 352598

1 files changed, 70 insertions, 52 deletions

diff --git a/llvm/test/CodeGen/WebAssembly/cfg-stackify-eh.ll b/llvm/test/CodeGen/WebAssembly/cfg-stackify-eh.ll
index e3c34f87e13..037730141b3 100644
--- a/llvm/test/CodeGen/WebAssembly/cfg-stackify-eh.ll
+++ b/llvm/test/CodeGen/WebAssembly/cfg-stackify-eh.ll
@@ -7,21 +7,25 @@ target triple = "wasm32-unknown-unknown"
 @_ZTId = external constant i8*
 
 ; Simple test case with two catch clauses
+; void test0() {
+;   try {
+;     foo();
+;   } catch (int n) {
+;     bar();
+;   } catch (double d) {
+;   }
+; }
 
 ; CHECK-LABEL: test0
+; CHECK:   try
 ; CHECK:   call      foo@FUNCTION
-; CHECK: .LBB0_1:
-; CHECK:   i32.catch
+; CHECK:   catch     $[[EXCEPT_REF:[0-9]+]]=
+; CHECK:   block i32
+; CHECK:   br_on_exn 0, __cpp_exception@EVENT, $[[EXCEPT_REF]]
+; CHECK:   rethrow
+; CHECK:   end_block
 ; CHECK:   i32.call  $drop=, _Unwind_CallPersonality@FUNCTION
-; CHECK:   i32.call  $drop=, __cxa_begin_catch@FUNCTION
-; CHECK:   call      bar@FUNCTION
-; CHECK:   call      __cxa_end_catch@FUNCTION
-; CHECK: .LBB0_3:
-; CHECK:   i32.call  $drop=, __cxa_begin_catch@FUNCTION
-; CHECK:   call      __cxa_end_catch@FUNCTION
-; CHECK: .LBB0_5:
-; CHECK:   call      __cxa_rethrow@FUNCTION
-; CHECK: .LBB0_6:
+; CHECK:   end_try
 ; CHECK:   return
 define void @test0() personality i8* bitcast (i32 (...)* @__gxx_wasm_personality_v0 to i8*) {
 entry:
@@ -68,39 +72,45 @@ try.cont:                                         ; preds = %entry, %catch, %cat
 }
 
 ; Nested try-catches within a catch
+; void test1() {
+;   try {
+;     foo();
+;   } catch (int n) {
+;     try {
+;       foo();
+;     } catch (int n) {
+;       foo();
+;     }
+;   }
+; }
 
 ; CHECK-LABEL: test1
+; CHECK:   try
 ; CHECK:   call      foo@FUNCTION
-; CHECK: .LBB1_1:
-; CHECK:   i32.catch     $0=, 0
-; CHECK:   i32.call  $drop=, _Unwind_CallPersonality@FUNCTION, $0
-; CHECK:   i32.call  $drop=, __cxa_begin_catch@FUNCTION, $0
-; CHECK:   call      foo@FUNCTION
-; CHECK: .LBB1_3:
-; CHECK:   i32.catch     $0=, 0
-; CHECK:   i32.call  $drop=, _Unwind_CallPersonality@FUNCTION, $0
-; CHECK:   i32.call  $drop=, __cxa_begin_catch@FUNCTION, $0
+; CHECK:   catch
+; CHECK:   br_on_exn 0, __cpp_exception@EVENT
+; CHECK:   rethrow
+; CHECK:   i32.call  $drop=, _Unwind_CallPersonality@FUNCTION
+; CHECK:   try
 ; CHECK:   call      foo@FUNCTION
-; CHECK: .LBB1_5:
-; CHECK:   catch_all
-; CHECK:   call      __cxa_end_catch@FUNCTION
+; CHECK:   catch
+; CHECK:   br_on_exn   0, __cpp_exception@EVENT
 ; CHECK:   rethrow
-; CHECK: .LBB1_6:
-; CHECK:   call      __cxa_rethrow@FUNCTION
+; CHECK:   i32.call  $drop=, _Unwind_CallPersonality@FUNCTION
+; CHECK:   try
+; CHECK:   i32.call  $drop=, __cxa_begin_catch@FUNCTION
+; CHECK:   try
+; CHECK:   call      foo@FUNCTION
+; CHECK:   catch     $drop=
 ; CHECK:   rethrow
-; CHECK: .LBB1_7:
-; CHECK:   call      __cxa_end_catch@FUNCTION
-; CHECK: .LBB1_8:
-; CHECK:   catch_all
-; CHECK:   call      __cxa_end_catch@FUNCTION
-; CHECK: .LBB1_9:
-; CHECK:   call      __cxa_rethrow@FUNCTION
+; CHECK:   end_try
+; CHECK:   catch     $drop=
 ; CHECK:   rethrow
-; CHECK: .LBB1_10:
-; CHECK:   call      __cxa_end_catch@FUNCTION
-; CHECK: .LBB1_11:
+; CHECK:   end_try
+; CHECK:   end_try
+; CHECK:   end_try
 ; CHECK:   return
-define hidden void @test1() personality i8* bitcast (i32 (...)* @__gxx_wasm_personality_v0 to i8*) {
+define void @test1() personality i8* bitcast (i32 (...)* @__gxx_wasm_personality_v0 to i8*) {
 entry:
   invoke void @foo()
           to label %try.cont11 unwind label %catch.dispatch
@@ -175,30 +185,38 @@ unreachable:                                      ; preds = %rethrow5
 }
 
 ; Nested loop within a catch clause
+; void test2() {
+;   try {
+;     foo();
+;   } catch (...) {
+;     for (int i = 0; i < 50; i++)
+;       foo();
+;   }
+; }
 
 ; CHECK-LABEL: test2
+; CHECK:   try
 ; CHECK:   call      foo@FUNCTION
-; CHECK: .LBB2_1:
-; CHECK:   i32.catch
-; CHECK:   i32.call  $drop=, __cxa_begin_catch@FUNCTION
-; CHECK: .LBB2_2:
+; CHECK:   catch
+; CHECK:   br_on_exn   0, __cpp_exception@EVENT
+; CHECK:   rethrow
+; CHECK:   loop
+; CHECK:   try
 ; CHECK:   call      foo@FUNCTION
-; CHECK: .LBB2_4:
-; CHECK:   catch_all
+; CHECK:   catch     $drop=
+; CHECK:   try
 ; CHECK:   call      __cxa_end_catch@FUNCTION
-; CHECK: .LBB2_5:
-; CHECK:   i32.catch
-; CHECK:   call      __clang_call_terminate@FUNCTION
+; CHECK:   catch
+; CHECK:   br_on_exn   0, __cpp_exception@EVENT
+; CHECK:   call      __clang_call_terminate@FUNCTION, 0
 ; CHECK:   unreachable
-; CHECK: .LBB2_6:
-; CHECK:   catch_all
-; CHECK:   call      _ZSt9terminatev@FUNCTION
+; CHECK:   call      __clang_call_terminate@FUNCTION
 ; CHECK:   unreachable
-; CHECK: .LBB2_7:
+; CHECK:   end_try
 ; CHECK:   rethrow
-; CHECK: .LBB2_8:
-; CHECK:   call      __cxa_end_catch@FUNCTION
-; CHECK: .LBB2_10:
+; CHECK:   end_try
+; CHECK:   end_loop
+; CHECK:   end_try
 ; CHECK:   return
 define void @test2() personality i8* bitcast (i32 (...)* @__gxx_wasm_personality_v0 to i8*) {
 entry: