[SEH] Fix wrong argument passes to the call of OutlinedFinally.

[jyu2]

Summary

When return out of __try block. In this test case, currently "false" is
passed to the OutlinedFinally call, "true" should be passed to indicate abnormal
terminations.

The rule: Except _leave and fall-through at the end, all other exits
in a _try (return/goto/continue/break) are considered as abnormal
terminations, NormalCleanupDestSlot is used to indicate abnormal
terminations.

The problem is, during the processing abnormal termination,
the ExitSwitch is used. However, in this case, Existswitch is route out.

One way to fix is to skip route it without a switch. So proper
abnormal termination's code could be generated.

IR before change:
invoke.cont: ; preds = %entry

invoke void @llvm.seh.try.begin()
        to label %invoke.cont1 unwind label %ehcleanup

invoke.cont1: ; preds = %invoke.cont

%1 = load volatile i32, ptr @y, align 4
%inc2 = add nsw i32 %1, 1
store volatile i32 %inc2, ptr @y, align 4
invoke void @llvm.seh.try.end()
        to label %invoke.cont3 unwind label %ehcleanup

invoke.cont3: ; preds = %invoke.cont1

%2 = call ptr @llvm.localaddress()
call void @"?fin$0@0@foo@@"(i8 noundef 0, ptr noundef %2)
ret void

IR after change:
invoke.cont: ; preds = %entry

invoke void @llvm.seh.try.begin()
        to label %invoke.cont1 unwind label %ehcleanup

invoke.cont1: ; preds = %invoke.cont

%1 = load volatile i32, ptr @y, align 4
%inc2 = add nsw i32 %1, 1
store volatile i32 %inc2, ptr @y, align 4
store volatile i32 1, ptr %cleanup.dest.slot, align 4
invoke void @llvm.seh.try.end()
        to label %invoke.cont3 unwind label %ehcleanup

invoke.cont3: ; preds = %invoke.cont1

%2 = call ptr @llvm.localaddress()
%cleanup.dest = load i32, ptr %cleanup.dest.slot, align 4
%3 = icmp ne i32 %cleanup.dest, 0
%4 = zext i1 %3 to i8
call void @"?fin$0@0@foo@@"(i8 noundef %4, ptr noundef %2)

...

[rnk]

clang/lib/CodeGen/CGCleanup.cpp

882

This seems like it's only necessary when exiting a __try scope, but this check affects all exits from C++ cleanup scopes. Is there a way to check if there is an active try scope? When do we need to signal abnormal termination via normal control flow?

[rnk]

clang/lib/CodeGen/CGCleanup.cpp

882

You can consider usesSEHTry , but it will require some type checking and casting: https://clang.llvm.org/doxygen/classclang_1_1FunctionDecl.html#a275d0f7f778c6ece58722aabde9b6d86

[jyu2]

clang/lib/CodeGen/CGCleanup.cpp

882

Thanks @rnk! That is good point. I was thinking I just turn off this optimization when EHa is used.

Can I use currentFunctionUsesSEHTry() instead?
Thanks.

[rnk]

lgtm, thanks!

clang/lib/CodeGen/CGCleanup.cpp

881

I think FD is unused now that you use currentFunctionUsesSEHTry

clang/lib/CodeGen/CGCleanup.cpp

// the cleanup block and then try to clean up after ourselves.
         BranchThroughDest = CreateNormalEntry(*this, cast<EHCleanupScope>(S));
       }
 
       llvm::BasicBlock *FallthroughDest = nullptr;
       SmallVector<llvm::Instruction*, 2> InstsToAppend;
 
       // If there's exactly one branch-after and no other threads,
       // we can route it without a switch.
+      // Skip for SEH, since ExitSwitch is used to generate code to indicate
+      // abnormal termination. (SEH: Except _leave and fall-through at
+      // the end, all other exits in a _try (return/goto/continue/break)
+      // are considered as abnormal terminations, using NormalCleanupDestSlot
+      // to indicate abnormal termination)
       if (!Scope.hasBranchThroughs() && !HasFixups && !HasFallthrough &&
-          Scope.getNumBranchAfters() == 1) {
+          !currentFunctionUsesSEHTry() && Scope.getNumBranchAfters() == 1) {
         assert(!BranchThroughDest || !IsActive);
 
         // Clean up the possibly dead store to the cleanup dest slot.
         llvm::Instruction *NormalCleanupDestSlot =
             cast<llvm::Instruction>(getNormalCleanupDestSlot().getPointer());
         if (NormalCleanupDestSlot->hasOneUse()) {
           NormalCleanupDestSlot->user_back()->eraseFromParent();
           NormalCleanupDestSlot->eraseFromParent();

clang/test/CodeGen/exceptions-seh-finally.c

 
 int finally_with_return(void) {
   __try {
     return 42;
   } __finally {
   }
 }
 // CHECK-LABEL: define dso_local i32 @finally_with_return()
+// CHECK: store i32 1, ptr %cleanup.dest.slot
+// CHECK: %cleanup.dest = load i32, ptr %cleanup.dest.slot
+// CHECK: icmp ne i32 %cleanup.dest
 // CHECK: call void @"?fin$0@0@finally_with_return@@"({{.*}})
-// CHECK-NEXT: ret i32 42
+// CHECK: ret i32 42
 
 // CHECK: define internal void @"?fin$0@0@finally_with_return@@"({{.*}})
 // CHECK-SAME: [[finally_attrs]]
 // CHECK-NOT: br i1
 // CHECK-NOT: br label
 // CHECK: ret void
 
 int nested___finally___finally(void) {

clang/test/CodeGen/windows-seh-EHa-TryInFinally.cpp

 // RUN: %clang_cc1 -triple x86_64-windows -fasync-exceptions -fcxx-exceptions -fexceptions -fms-extensions -x c++ -Wno-implicit-function-declaration -S -emit-llvm %s -o - | FileCheck %s
 
+// CHECK-LABEL: @main()
 // CHECK: invoke void @llvm.seh.try.begin()
 // CHECK: invoke void @llvm.seh.try.begin()
 // CHECK: %[[src:[0-9-]+]] = load volatile i32, ptr %i
 // CHECK-NEXT: i32 noundef %[[src]]
 // CHECK: invoke void @llvm.seh.try.end()
 // CHECK: invoke void @llvm.seh.try.end()
 
 // CHECK: define internal void @"?fin$0@0@main@@"(i8 noundef %abnormal_termination
__try {
         }
       }
     } __except (1) {
       printf(" --- In outer except handler i = %d \n", i);
     }
   }
   return 0;
 }
+
+// CHECK-LABEL:@"?foo@@YAXXZ"()
+// CHECK: invoke.cont:
+// CHECK: invoke void @llvm.seh.try.begin()
+// CHECK: store volatile i32 1, ptr %cleanup.dest.slot
+// CHECK: invoke void @llvm.seh.try.end()
+// CHECK: invoke.cont2:
+// CHECK: %cleanup.dest = load i32, ptr %cleanup.dest.slot
+// CHECK: %1 = icmp ne i32 %cleanup.dest, 0
+// CHECK: %2 = zext i1 %1 to i8
+// CHECK: call void @"?fin$0@0@foo@@"(i8 noundef %2, ptr noundef %0)
+// CHECK: ehcleanup:
+// CHECK: call void @"?fin$0@0@foo@@"(i8 noundef 1, ptr noundef %4)
+void foo()
+{
+  __try {
+    return;
+  }
+  __finally {
+    if (_abnormal_termination()) {
+      printf("Passed\n");
+    } else {
+      printf("Failed\n");
+    }
+  }
+}