[WebAssembly] Simplify a switch-case in CFGStackify (NFC) (#107360)

This merges some `case`s using `[[fallthrough]]`, and make `DELEGATE` as
a separate `case`. (Previously the reason we didn't do that was not to
duplicate the code in `RewriteOperands`. But now that we've extracted it
into a lambda function in #107182 we can do it.

Author: aheejin

llvm/lib/Target/WebAssembly/WebAssemblyCFGStackify.cpp

@@ -1681,18 +1681,14 @@ void WebAssemblyCFGStackify::rewriteDepthImmediates(MachineFunction &MF) {
         Stack.pop_back();
         break;
 
-      case WebAssembly::END_BLOCK:
-        Stack.push_back(std::make_pair(&MBB, &MI));
-        break;
-
       case WebAssembly::END_TRY: {
-        // We handle DELEGATE in the default level, because DELEGATE has
-        // immediate operands to rewrite.
-        Stack.push_back(std::make_pair(&MBB, &MI));
         auto *EHPad = TryToEHPad[EndToBegin[&MI]];
         EHPadStack.push_back(EHPad);
-        break;
+        [[fallthrough]];
       }
+      case WebAssembly::END_BLOCK:
+        Stack.push_back(std::make_pair(&MBB, &MI));
+        break;
 
       case WebAssembly::END_LOOP:
         Stack.push_back(std::make_pair(EndToBegin[&MI]->getParent(), &MI));
@@ -1707,12 +1703,14 @@ void WebAssemblyCFGStackify::rewriteDepthImmediates(MachineFunction &MF) {
         MI.getOperand(0).setImm(getRethrowDepth(Stack, EHPadStack));
         break;
 
+      case WebAssembly::DELEGATE:
+        RewriteOperands(MI);
+        Stack.push_back(std::make_pair(&MBB, &MI));
+        break;
+
       default:
         if (MI.isTerminator())
           RewriteOperands(MI);
-
-        if (MI.getOpcode() == WebAssembly::DELEGATE)
-          Stack.push_back(std::make_pair(&MBB, &MI));
         break;
       }
     }

llvm/lib/Target/WebAssembly/WebAssemblyInstrControl.td

@@ -147,9 +147,9 @@ let isTerminator = 1, hasSideEffects = 1, isBarrier = 1, hasCtrlDep = 1,
 // usage gets low enough.
 
 // Rethrowing an exception: rethrow
-let isTerminator = 1, hasCtrlDep = 1, isBarrier = 1 in {
+let isTerminator = 1, hasCtrlDep = 1, isBarrier = 1 in
 defm RETHROW : NRI<(outs), (ins i32imm:$depth), [], "rethrow \t$depth", 0x09>;
-} // isTerminator = 1, hasCtrlDep = 1, isBarrier = 1
+// isTerminator = 1, hasCtrlDep = 1, isBarrier = 1
 // The depth argument will be computed in CFGStackify. We set it to 0 here for
 // now.
 def : Pat<(int_wasm_rethrow), (RETHROW 0)>;