[WebAssembly] Handle multiple EH_LABELs in EH pad

Usually `EH_LABEL`s are placed in
- Before an `invoke` (which becomes calls in the backend)
- After an `invoke`
- At the start of an EH pad

I don't know exactly why, but I noticed there are cases of multiple, not
a single, `EH_LABEL` instructions in the beginning of an EH pad. In that
case `global.set` instruction placed to restore `__stack_pointer` ended
up between two `EH_LABEL` instructions before `CATCH`. It should follow
after the `EH_LABEL`s and `CATCH`. This CL fixes that case.

Reviewed By: dschuff

Differential Revision: https://reviews.llvm.org/D96970

llvm/lib/Target/WebAssembly/WebAssemblyLateEHPrepare.cpp

@@ -212,7 +212,7 @@ bool WebAssemblyLateEHPrepare::addCatchAlls(MachineFunction &MF) {
     while (InsertPos != MBB.end() && InsertPos->isEHLabel())
       InsertPos++;
     // This runs after hoistCatches(), so we assume that if there is a catch,
-    // that should be the non-EH label first instruction in an EH pad.
+    // that should be the first non-EH-label instruction in an EH pad.
     if (InsertPos == MBB.end() ||
         !WebAssembly::isCatch(InsertPos->getOpcode())) {
       Changed = true;
@@ -383,10 +383,13 @@ bool WebAssemblyLateEHPrepare::restoreStackPointer(MachineFunction &MF) {
     // with leaf functions, and we don't restore __stack_pointer in leaf
     // functions anyway.
     auto InsertPos = MBB.begin();
-    if (InsertPos->isEHLabel()) // EH pad starts with an EH label
-      ++InsertPos;
-    if (WebAssembly::isCatch(InsertPos->getOpcode()))
-      ++InsertPos;
+    // Skip EH_LABELs in the beginning of an EH pad if present.
+    while (InsertPos != MBB.end() && InsertPos->isEHLabel())
+      InsertPos++;
+    assert(InsertPos != MBB.end() &&
+           WebAssembly::isCatch(InsertPos->getOpcode()) &&
+           "catch/catch_all should be present in every EH pad at this point");
+    ++InsertPos; // Skip the catch instruction
     FrameLowering->writeSPToGlobal(FrameLowering->getSPReg(MF), MF, MBB,
                                    InsertPos, MBB.begin()->getDebugLoc());
   }

llvm/test/CodeGen/WebAssembly/exception.mir

@@ -24,6 +24,8 @@
 name: eh_label_test
 liveins:
   - { reg: '$arguments' }
+frameInfo:
+  hasCalls: true
 body: |
   bb.0:
     ; TRY should be before EH_LABEL wrappers of throwing calls
@@ -41,10 +43,15 @@ body: |
   bb.1 (landing-pad):
   ; predecessors: %bb.0
     successors: %bb.2
-    ; CATCH_ALL should be after an EH_LABEL at the beginning of an EH pad
+    ; CATCH_ALL should be after EH_LABELs in the beginning of an EH pad.
+    ; (Sometimes there are multiple EH_LABELs in an EH pad. This test tests
+    ; that.) GLOBAL_SET should follow right after that.
     ; CHECK:      bb.1
     ; CHECK:      EH_LABEL
+    ; CHECK:      EH_LABEL
     ; CHECK-NEXT: CATCH_ALL
+    ; CHECK-NEXT: GLOBAL_SET_I32
+    EH_LABEL <mcsymbol .Ltmp2>
     EH_LABEL <mcsymbol .Ltmp2>
     CATCHRET %bb.2, %bb.1, implicit-def dead $arguments