[WebAssembly] Fix bugs in BLOCK/TRY placement

Summary:
Before we placed all TRY/END_TRY markers before placing BLOCK/END_BLOCK
markers. This couldn't handle this case:
```
bb0:
  br bb2
bb1:          // nearest common dominator of bb3 and bb4
  br_if ... bb3
  br bb4
bb2:
  ...
bb3:
  call @foo   // unwinds to ehpad
bb4:
  call @bar   // unwinds to ehpad
ehpad:
  catch
  ...
```

When we placed TRY markers, we placed it in bb1 because it is the
nearest common dominator of bb3 and bb4. But because bb0 jumps to bb2,
when we placed block markers, we ended up with interleaved scopes like
```
block
try
end_block
catch
end_try
```
which was not correct.

This patch fixes the bug by placing BLOCK and TRY markers in one pass
while iterating BBs in a function. This also adds some more routines to
`placeTryMarkers`, because we now have to assume that there can be
previously placed BLOCK and END_BLOCK.

Reviewers: dschuff

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

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D59739

llvm-svn: 357007

1 files changed, 52 insertions, 3 deletions

diff --git a/llvm/test/CodeGen/WebAssembly/cfg-stackify-eh.ll b/llvm/test/CodeGen/WebAssembly/cfg-stackify-eh.ll
index 5b06a0baa35..f0f49344cfc 100644
--- a/llvm/test/CodeGen/WebAssembly/cfg-stackify-eh.ll
+++ b/llvm/test/CodeGen/WebAssembly/cfg-stackify-eh.ll
@@ -1,4 +1,5 @@
 ; RUN: llc < %s -disable-wasm-fallthrough-return-opt -wasm-disable-explicit-locals -wasm-keep-registers -disable-block-placement -verify-machineinstrs -fast-isel=false -machine-sink-split-probability-threshold=0 -cgp-freq-ratio-to-skip-merge=1000 -exception-model=wasm -mattr=+exception-handling | FileCheck %s
+; RUN: llc < %s -O0 -disable-wasm-fallthrough-return-opt -wasm-disable-explicit-locals -wasm-keep-registers -verify-machineinstrs -exception-model=wasm -mattr=+exception-handling | FileCheck %s --check-prefix=NOOPT
 
 target datalayout = "e-m:e-p:32:32-i64:64-n32:64-S128"
 target triple = "wasm32-unknown-unknown"
@@ -70,7 +71,7 @@ rethrow:                                          ; preds = %catch.fallthrough
   call void @llvm.wasm.rethrow.in.catch() [ "funclet"(token %1) ]
   unreachable
 
-try.cont:                                         ; preds = %entry, %catch, %catch2
+try.cont:                                         ; preds = %catch, %catch2, %entry
   ret void
 }
 
@@ -173,7 +174,7 @@ rethrow5:                                         ; preds = %catch.start3
   invoke void @llvm.wasm.rethrow.in.catch() [ "funclet"(token %9) ]
           to label %unreachable unwind label %ehcleanup9
 
-try.cont:                                         ; preds = %catch, %invoke.cont8
+try.cont:                                         ; preds = %invoke.cont8, %catch
   call void @__cxa_end_catch() [ "funclet"(token %1) ]
   catchret from %1 to label %try.cont11
 
@@ -181,7 +182,7 @@ rethrow:                                          ; preds = %catch.start
   call void @llvm.wasm.rethrow.in.catch() [ "funclet"(token %1) ]
   unreachable
 
-try.cont11:                                       ; preds = %entry, %try.cont
+try.cont11:                                       ; preds = %try.cont, %entry
   ret void
 
 ehcleanup:                                        ; preds = %catch6
@@ -286,6 +287,54 @@ terminate:                                        ; preds = %ehcleanup
   unreachable
 }
 
+; Tests if block and try markers are correctly placed. Even if two predecessors
+; of the EH pad are bb2 and bb3 and their nearest common dominator is bb1, the
+; TRY marker should be placed at bb0 because there's a branch from bb0 to bb2,
+; and scopes cannot be interleaved.
+
+; NOOPT-LABEL: test3
+; NOOPT: try
+; NOOPT:   block
+; NOOPT:     block
+; NOOPT:       block
+; NOOPT:       end_block
+; NOOPT:     end_block
+; NOOPT:     call      foo
+; NOOPT:   end_block
+; NOOPT:   call      bar
+; NOOPT: catch     {{.*}}
+; NOOPT: end_try
+define void @test3() personality i8* bitcast (i32 (...)* @__gxx_wasm_personality_v0 to i8*) {
+bb0:
+  br i1 undef, label %bb1, label %bb2
+
+bb1:                                              ; preds = %bb0
+  br i1 undef, label %bb3, label %bb4
+
+bb2:                                              ; preds = %bb0
+  br label %try.cont
+
+bb3:                                              ; preds = %bb1
+  invoke void @foo()
+          to label %try.cont unwind label %catch.dispatch
+
+bb4:                                              ; preds = %bb1
+  invoke void @bar()
+          to label %try.cont unwind label %catch.dispatch
+
+catch.dispatch:                                   ; preds = %bb4, %bb3
+  %0 = catchswitch within none [label %catch.start] unwind to caller
+
+catch.start:                                      ; preds = %catch.dispatch
+  %1 = catchpad within %0 [i8* null]
+  %2 = call i8* @llvm.wasm.get.exception(token %1)
+  %3 = call i32 @llvm.wasm.get.ehselector(token %1)
+  catchret from %1 to label %try.cont
+
+try.cont:                                         ; preds = %catch.start, %bb4, %bb3, %bb2
+  ret void
+}
+
 declare void @foo()
 declare void @bar()
 declare i32 @__gxx_wasm_personality_v0(...)