[WebAssembly] Do not use EHCatchret symbols with wasm EH

[dschuff]

Summary

D94835 (revision 080866470d3e ) added support for WinEH to export public symbols pointing to
basic blocks which are catchret targets for use with Windows CET.
Wasm currently doesn't support public symbols to non-function code
addresses (they get treated like new functions in asm but then don't
lower to object files correctly).
It created them unconditionally for all catchret targets.

This change disables those symbols unless the exceptionHandlingType
is WinEH (since they aren't used with ExceptionHandling::Wasm)

[dschuff]

This test is basically copied from llvm/test/CodeGen/X86/win-catchpad-nested.ll which is a configuration that triggers the labels. It doesn't have the itanium-personality stuff that wasm EH code usually does. But does it look like a sane test?

[aheejin]

Thanks for taking care of this. I think the test case is fine, but it'd better to make it a valid wasm EH file, because in the current state does not generate a valid wasm code. I made edits to do that so you can just apply them.

llvm/test/CodeGen/WebAssembly/eh-catchpad-nested.ll

6 ↗

(On Diff #324136)

10 ↗

(On Diff #324136)

21 ↗

(On Diff #324136)

%cp1 = catchpad within %cs1 [i32 1]
%0 = call i8* @llvm.wasm.get.exception(token %cp1)
%1 = call i32 @llvm.wasm.get.ehselector(token %cp1)

28 ↗

(On Diff #324136)

newline

30 ↗

(On Diff #324136)

%cp2 = catchpad within %cs2 [i32 2]
%2 = call i8* @llvm.wasm.get.exception(token %cp2)
%3 = call i32 @llvm.wasm.get.ehselector(token %cp2)

[aheejin]

Sorry, on second thought, I don't even think we need a new test case for this. All existing exception-using test cases will show the same behavior, so I think you can add

; Check that no $ehgcr symbols are emitted
; CHECK-NOT: $ehgcr

to somewhere like test/CodeGen/WebAssebly/exception.ll.

[dschuff]

Ah, you are right, I initially thought that we needed a new test because none of ours failed when their patch went in. But the reason for that was that the output is all assembly rather than object files.
I added --implicit-check-not to exception.ll and that does catch the error.

[dschuff]

Update existing test instead of using new one

[dschuff]

fix diff

llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp

void AsmPrinter::emitBasicBlockStart(const MachineBasicBlock &MBB) {
   } else {
     if (isVerbose()) {
       // NOTE: Want this comment at start of line, don't emit with AddComment.
       OutStreamer->emitRawComment(" %bb." + Twine(MBB.getNumber()) + ":",
                                   false);
     }
   }
 
-  if (MBB.isEHCatchretTarget()) {
+  if (MBB.isEHCatchretTarget() &&
+      MAI->getExceptionHandlingType() == ExceptionHandling::WinEH) {
     OutStreamer->emitLabel(MBB.getEHCatchretSymbol());
   }
 
   // With BB sections, each basic block must handle CFI information on its own
   // if it begins a section (Entry block is handled separately by
   // AsmPrinterHandler::beginFunction).
   if (MBB.isBeginSection() && !MBB.isEntryBlock())
     for (const HandlerInfo &HI : Handlers)

llvm/test/CodeGen/WebAssembly/exception.ll

-; RUN: llc < %s -asm-verbose=false -disable-wasm-fallthrough-return-opt -wasm-disable-explicit-locals -wasm-keep-registers -exception-model=wasm -mattr=+exception-handling -verify-machineinstrs | FileCheck -allow-deprecated-dag-overlap %s
+; RUN: llc < %s -asm-verbose=false -disable-wasm-fallthrough-return-opt -wasm-disable-explicit-locals -wasm-keep-registers -exception-model=wasm -mattr=+exception-handling -verify-machineinstrs | FileCheck --implicit-check-not=ehgcr -allow-deprecated-dag-overlap %s
 ; RUN: llc < %s -asm-verbose=false -disable-wasm-fallthrough-return-opt -wasm-disable-explicit-locals -wasm-keep-registers -exception-model=wasm -mattr=+exception-handling -verify-machineinstrs -O0 | FileCheck -allow-deprecated-dag-overlap --check-prefix=NOOPT %s
 ; RUN: llc < %s -disable-wasm-fallthrough-return-opt -wasm-keep-registers -exception-model=wasm -mattr=+exception-handling
 
 target datalayout = "e-m:e-p:32:32-i64:64-n32:64-S128"
 target triple = "wasm32-unknown-unknown"
 
 %struct.Temp = type { i8 }