[CIR] Early return in emitCXXTryStmt if try block is empty (#1944)

Currently, in the case of an empty try block, we emit tryOp in scope and
revisit the catchers, and in the lowering pass, we have a check to
delete empty scopes, but we end up with scopes that contains `cir.yeild`
or an unconditioned jump to another scope which will not be deleted,
also for catchers we emits globals for type info.


But we can already ignore the try-catch statement if the try block is
empty, because that means also all catchers are dead code, which will
lead to not emitting any scopes that we know will be removed later and
also not emitting any unnecessary type info

Example of current emitted IR: https://godbolt.org/z/5d3jEe5K8

Author: AmrDeveloper

clang/lib/CIR/CodeGen/CIRGenException.cpp

@@ -302,6 +302,9 @@ mlir::Block *CIRGenFunction::getEHResumeBlock(bool isCleanup,
 }
 
 mlir::LogicalResult CIRGenFunction::emitCXXTryStmt(const CXXTryStmt &S) {
+  if (S.getTryBlock()->body_empty())
+    return mlir::LogicalResult::success();
+
   auto loc = getLoc(S.getSourceRange());
   mlir::OpBuilder::InsertPoint scopeIP;
 

clang/test/CIR/CodeGen/empty-try-catch.cpp

@@ -0,0 +1,33 @@
+// RUN: %clang_cc1 -std=c++20 -triple x86_64-unknown-linux-gnu -fcxx-exceptions -fexceptions -fclangir -emit-cir %s -o %t.cir
+// RUN: FileCheck --input-file=%t.cir %s -check-prefix=CIR
+// RUN: %clang_cc1 -std=c++20 -triple x86_64-unknown-linux-gnu -fcxx-exceptions -fexceptions -fclangir -emit-llvm %s -o %t-cir.ll
+// RUN: FileCheck --input-file=%t-cir.ll %s -check-prefix=LLVM
+// RUN: %clang_cc1 -std=c++20 -triple x86_64-unknown-linux-gnu -fcxx-exceptions -fexceptions -emit-llvm %s -o %t.ll
+// RUN: FileCheck --input-file=%t.ll %s -check-prefix=OGCG
+
+void empty_try_block_with_catch_all() {
+  try {} catch (...) {}
+}
+
+// CIR: cir.func{{.*}} @_Z30empty_try_block_with_catch_allv()
+// CIR:   cir.return
+
+// LLVM: define{{.*}} void @_Z30empty_try_block_with_catch_allv()
+// LLVM:  ret void
+
+// OGCG: define{{.*}} void @_Z30empty_try_block_with_catch_allv()
+// OGCG:   ret void
+
+void empty_try_block_with_catch_with_int_exception() {
+  try {} catch (int e) {}
+}
+
+// CIR: cir.func{{.*}} @_Z45empty_try_block_with_catch_with_int_exceptionv()
+// CIR:   cir.return
+
+// LLVM: define{{.*}} void @_Z45empty_try_block_with_catch_with_int_exceptionv()
+// LLVM:  ret void
+
+// OGCG: define{{.*}} void @_Z45empty_try_block_with_catch_with_int_exceptionv()
+// OGCG:   ret void
+