[CIR][CodeGen] Emit cir.resume for synthetic TryOp's in place (#1418)

Currently, the following code snippet fails during CIR codegen with
exceptions enabled:
```
#include <string>

void foo(const char *path) {
  std::string str = path;
  str = path;
  str = path;
}
```
using `bin/clang++ tmp.cpp -fclangir -Xclang -emit-cir -S`, the error: 
```
error: empty block: expect at least a terminator
```
Relevant part of the CIR before verification looks like: 
```
%118 = "cir.load"(%114) : (!cir.ptr<!cir.ptr<!cir.int<s, 8>>>) -> !cir.ptr<!cir.int<s, 8>>
"cir.try"() <{catch_types = [#cir.unwind], cleanup, synthetic}> ({
    %123 = "cir.call"(%115, %118) <{ast = #cir.call.expr.ast, callee = @_ZNSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEEaSEPKc, calling_conv = 1 : i32, exception, extra_attrs = #cir<extra({})>, side_effect = 1 : i32}> ({
    "cir.call"(%115) <{callee = @_ZNSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEED1Ev, calling_conv = 1 : i32, extra_attrs = #cir<extra({nothrow = #cir.nothrow})>, side_effect = 1 : i32}> ({
    }) : (!cir.ptr<!cir.struct<class "std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>" {!cir.struct<struct "std::__cxx11::basic_string<char>::_Alloc_hider" {!cir.ptr<!cir.int<s, 8>>} #cir.record.decl.ast>, !cir.int<u, 64>, !cir.struct<union "anon.0" padded {!cir.array<!cir.int<s, 8> x 16>, !cir.int<u, 64>, !cir.array<!cir.int<u, 8> x 8>} #cir.record.decl.ast>} #cir.record.decl.ast>>) -> ()
    "cir.yield"() : () -> ()
    }) : (!cir.ptr<!cir.struct<class "std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>" {!cir.struct<struct "std::__cxx11::basic_string<char>::_Alloc_hider" {!cir.ptr<!cir.int<s, 8>>} #cir.record.decl.ast>, !cir.int<u, 64>, !cir.struct<union "anon.0" padded {!cir.array<!cir.int<s, 8> x 16>, !cir.int<u, 64>, !cir.array<!cir.int<u, 8> x 8>} #cir.record.decl.ast>} #cir.record.decl.ast>>, !cir.ptr<!cir.int<s, 8>>) -> !cir.ptr<!cir.struct<class "std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>" {!cir.struct<struct "std::__cxx11::basic_string<char>::_Alloc_hider" {!cir.ptr<!cir.int<s, 8>>} #cir.record.decl.ast>, !cir.int<u, 64>, !cir.struct<union "anon.0" padded {!cir.array<!cir.int<s, 8> x 16>, !cir.int<u, 64>, !cir.array<!cir.int<u, 8> x 8>} #cir.record.decl.ast>} #cir.record.decl.ast>>
    "cir.store"(%123, %116) : (!cir.ptr<!cir.struct<class "std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>" {!cir.struct<struct "std::__cxx11::basic_string<char>::_Alloc_hider" {!cir.ptr<!cir.int<s, 8>>} #cir.record.decl.ast>, !cir.int<u, 64>, !cir.struct<union "anon.0" padded {!cir.array<!cir.int<s, 8> x 16>, !cir.int<u, 64>, !cir.array<!cir.int<u, 8> x 8>} #cir.record.decl.ast>} #cir.record.decl.ast>>, !cir.ptr<!cir.ptr<!cir.struct<class "std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>" {!cir.struct<struct "std::__cxx11::basic_string<char>::_Alloc_hider" {!cir.ptr<!cir.int<s, 8>>} #cir.record.decl.ast>, !cir.int<u, 64>, !cir.struct<union "anon.0" padded {!cir.array<!cir.int<s, 8> x 16>, !cir.int<u, 64>, !cir.array<!cir.int<u, 8> x 8>} #cir.record.decl.ast>} #cir.record.decl.ast>>>) -> ()
    "cir.yield"() : () -> ()
}, {
^bb0:              <--- EMPTY BLOCK
}) : () -> ()
```
There is an empty block! If you extend the snippet with more `str =
path;`, you get more empty blocks...

The issue is the `cir.resume` ops which should be in those empty blocks
from synthetic TryOp's aren't linked properly during the cleanup.

My suggestion: We should explicitly add `cir.resume` for synthetic
tryOp's, because we already know they have just an [unwind
handler](https://github.com/llvm/clangir/blob/8746bd4bbe777352c2935e9937449637a8943767/clang/lib/CIR/CodeGen/CIRGenCall.cpp#L506).
So, during
[CIRGenCleanup](https://github.com/llvm/clangir/blob/8746bd4bbe777352c2935e9937449637a8943767/clang/lib/CIR/CodeGen/CIRGenCleanup.cpp#L667)
we don't need to add `cir.resume` for synthetic TryOp's. This PR adds
this and a test.

Author: bruteforceboy

clang/lib/CIR/CodeGen/CIRGenCall.cpp

@@ -507,6 +507,7 @@ emitCallLikeOp(CIRGenFunction &CGF, mlir::Location callLoc,
           // handler: unwind.
           auto *r = result.addRegion();
           builder.createBlock(r);
+          builder.create<cir::ResumeOp>(loc, mlir::Value{}, mlir::Value{});
         });
     op.setSynthetic(true);
     return op;

clang/lib/CIR/CodeGen/CIRGenCleanup.cpp

@@ -666,10 +666,12 @@ void CIRGenFunction::PopCleanupBlock(bool FallthroughIsBranchThrough) {
         if (nextAction == ehResumeBlock) {
           if (auto tryToPatch =
                   currYield->getParentOp()->getParentOfType<cir::TryOp>()) {
-            mlir::Block *resumeBlockToPatch =
-                tryToPatch.getCatchUnwindEntryBlock();
-            emitEHResumeBlock(/*isCleanup=*/true, resumeBlockToPatch,
-                              tryToPatch.getLoc());
+            if (!tryToPatch.getSynthetic()) {
+              mlir::Block *resumeBlockToPatch =
+                  tryToPatch.getCatchUnwindEntryBlock();
+              emitEHResumeBlock(/*isCleanup=*/true, resumeBlockToPatch,
+                                tryToPatch.getLoc());
+            }
           }
         }
 

clang/test/CIR/CodeGen/synthetic-try-resume.cpp

@@ -0,0 +1,89 @@
+// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -fcxx-exceptions -fexceptions -I%S/../Inputs -fclangir -emit-cir %s -o %t.cir
+// RUN: FileCheck --check-prefix=CIR --input-file=%t.cir %s
+// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -fcxx-exceptions -fexceptions -I%S/../Inputs -fclangir -emit-llvm %s -o %t.ll
+// RUN: FileCheck --check-prefix=LLVM --input-file=%t.ll %s
+
+#include "std-cxx.h"
+
+// CIR-LABEL:  @_Z3fooPKc
+// LLVM-LABEL: @_Z3fooPKc
+
+void foo(const char* path) {
+  std::string str = path;
+  str = path;
+  str = path;
+}
+
+// CIR: cir.try synthetic cleanup {
+// CIR:   cir.call exception @_ZNSbIcEC1EPKcRKNS_9AllocatorE({{.*}}, {{.*}}, {{.*}}) : (!cir.ptr<!ty_std3A3Abasic_string3Cchar3E>, !cir.ptr<!s8i>, !cir.ptr<!ty_std3A3Abasic_string3Cchar3E3A3AAllocator>) -> () cleanup {
+// CIR:     cir.call @_ZNSbIcED1Ev({{.*}}) : (!cir.ptr<!ty_std3A3Abasic_string3Cchar3E>) -> ()
+// CIR:     cir.yield
+// CIR:   }
+// CIR:   cir.yield
+// CIR: } catch [#cir.unwind {
+// CIR:   cir.resume
+// CIR: }]
+// CIR: cir.try synthetic cleanup {
+// CIR:   {{.*}} = cir.call exception @_ZNSbIcEaSERKS_({{.*}}, {{.*}}) : (!cir.ptr<!ty_std3A3Abasic_string3Cchar3E>, !cir.ptr<!ty_std3A3Abasic_string3Cchar3E>) -> !cir.ptr<!ty_std3A3Abasic_string3Cchar3E> cleanup {
+// CIR:     cir.call @_ZNSbIcED1Ev({{.*}}) : (!cir.ptr<!ty_std3A3Abasic_string3Cchar3E>) -> ()
+// CIR:     cir.yield
+// CIR:   }
+// CIR:   cir.store {{.*}}, {{.*}} : !cir.ptr<!ty_std3A3Abasic_string3Cchar3E>, !cir.ptr<!cir.ptr<!ty_std3A3Abasic_string3Cchar3E>>
+// CIR:   cir.yield
+// CIR: } catch [#cir.unwind {
+// CIR:   cir.resume
+// CIR: }]
+// CIR: {{.*}} = cir.load {{.*}} : !cir.ptr<!cir.ptr<!ty_std3A3Abasic_string3Cchar3E>>, !cir.ptr<!ty_std3A3Abasic_string3Cchar3E>
+// CIR: cir.call @_ZNSbIcED1Ev({{.*}}) : (!cir.ptr<!ty_std3A3Abasic_string3Cchar3E>) -> ()
+// CIR: cir.try synthetic cleanup {
+// CIR:   cir.call exception @_ZNSbIcEC1EPKcRKNS_9AllocatorE({{.*}}, {{.*}}, {{.*}}) : (!cir.ptr<!ty_std3A3Abasic_string3Cchar3E>, !cir.ptr<!s8i>, !cir.ptr<!ty_std3A3Abasic_string3Cchar3E3A3AAllocator>) -> ()
+// CIR:   cir.yield
+// CIR: } catch [#cir.unwind {
+// CIR:   cir.resume
+// CIR: }]
+// CIR: cir.try synthetic cleanup {
+// CIR:   {{.*}} = cir.call exception @_ZNSbIcEaSERKS_({{.*}}, {{.*}}) : (!cir.ptr<!ty_std3A3Abasic_string3Cchar3E>, !cir.ptr<!ty_std3A3Abasic_string3Cchar3E>) -> !cir.ptr<!ty_std3A3Abasic_string3Cchar3E> cleanup {
+// CIR:     cir.call @_ZNSbIcED1Ev({{.*}}) : (!cir.ptr<!ty_std3A3Abasic_string3Cchar3E>) -> ()
+// CIR:     cir.call @_ZNSbIcED1Ev({{.*}}) : (!cir.ptr<!ty_std3A3Abasic_string3Cchar3E>) -> ()
+// CIR:     cir.yield
+// CIR:   }
+// CIR:   cir.store {{.*}}, {{.*}} : !cir.ptr<!ty_std3A3Abasic_string3Cchar3E>, !cir.ptr<!cir.ptr<!ty_std3A3Abasic_string3Cchar3E>>
+// CIR:   cir.yield
+// CIR: } catch [#cir.unwind {
+// CIR:   cir.resume
+// CIR: }]
+
+// LLVM:  invoke void @_ZNSbIcEC1EPKcRKNS_9AllocatorE(ptr {{.*}}, ptr {{.*}}, ptr {{.*}})
+// LLVM:           to label {{.*}} unwind label %[[B18:.*]]
+// LLVM: [[B18]]
+// LLVM:   call void @_ZNSbIcED1Ev(ptr {{.*}})
+// LLVM:   br label %[[B22:.*]]
+// LLVM: [[B22]]
+// LLVM:   resume { ptr, i32 } {{.*}}
+// LLVM: {{.*}}:
+// LLVM:   {{.*}} = invoke ptr @_ZNSbIcEaSERKS_(ptr {{.*}}, ptr {{.*}})
+// LLVM:           to label {{.*}} unwind label %[[B31:.*]]
+// LLVM: [[B31]]
+// LLVM:   call void @_ZNSbIcED1Ev(ptr {{.*}})
+// LLVM:   br label %[[B35:.*]]
+// LLVM: [[B35]]
+// LLVM:   resume { ptr, i32 } {{.*}}
+// LLVM: {{.*}}:
+// LLVM:   call void @_ZNSbIcED1Ev(ptr {{.*}})
+// LLVM:   br label {{.*}}
+// LLVM: {{.*}}:
+// LLVM:   invoke void @_ZNSbIcEC1EPKcRKNS_9AllocatorE(ptr {{.*}}, ptr {{.*}}, ptr {{.*}})
+// LLVM:           to label {{.*}} unwind label %[[B46:.*]]
+// LLVM: [[B46]]
+// LLVM:   br label %[[B50:.*]]
+// LLVM: [[B50]]
+// LLVM:   resume { ptr, i32 } {{.*}}
+// LLVM: {{.*}}:
+// LLVM:   {{.*}} = invoke ptr @_ZNSbIcEaSERKS_(ptr {{.*}}, ptr {{.*}})
+// LLVM:           to label {{.*}} unwind label %[[B59:.*]]
+// LLVM: [[B59]]
+// LLVM:   call void @_ZNSbIcED1Ev(ptr {{.*}})
+// LLVM:   call void @_ZNSbIcED1Ev(ptr {{.*}})
+// LLVM:   br label %[[B63:.*]]
+// LLVM: [[B63]]
+// LLVM:   resume { ptr, i32 } {{.*}}