[WebAssembly] Fix immediate of rethrow when throwing to caller

[aheejin]

Summary

Currently when assigning depths 'rethrow' does not take the whole
control flow stack into accounts but only considers EH pad stacks. When
assigning depth immmediates to rethrows, in normal cases it is done
correctly but when a rethrow instruction throws up to a caller, i.e., we
convert a pseudo RETHROW_TO_CALLER instruction to a rethrow, it
mistakenly compute the whole stack depth.

[aheejin]

Ping

llvm/trunk/lib/Target/WebAssembly/WebAssemblyCFGStackify.cpp

for (auto I = MBB.rbegin(), E = MBB.rend(); I != E; ++I) {
         MI.RemoveOperand(0);
         MI.addOperand(MF, MachineOperand::CreateImm(EHPadDepth));
         break;
       }
 
       case WebAssembly::RETHROW_TO_CALLER: {
         MachineInstr *Rethrow =
             BuildMI(MBB, MI, MI.getDebugLoc(), TII.get(WebAssembly::RETHROW))
-                .addImm(Stack.size());
+                .addImm(EHPadStack.size());
         MI.eraseFromParent();
         I = MachineBasicBlock::reverse_iterator(Rethrow);
         break;
       }
 
       default:
         if (MI.isTerminator()) {
           // Rewrite MBB operands to be depth immediates.

llvm/trunk/test/CodeGen/WebAssembly/cfg-stackify-eh.mir

body: |
 
   bb.7:
   ; predecessors: %bb.1
 
     CALL_VOID @__cxa_rethrow, implicit-def dead $arguments, implicit $sp32, implicit $sp64
     RETHROW_TO_CALLER implicit-def $arguments
   ; CHECK-LABEL: bb.7:
     ; CHECK-NEXT: END_TRY
-    ; CHECK: RETHROW 3
+    ; CHECK: RETHROW 0
 
   bb.8:
   ; predecessors: %bb.2, %bb.4
     successors: %bb.9
 
     CALL_VOID @__cxa_end_catch, implicit-def dead $arguments, implicit $sp32, implicit $sp64
 
   bb.9: