Implement CFG construction for __try / __except / __leave.

This makes -Wunreachable-code work for programs containing SEH (except for
__finally, which is still missing for now).

__try is modeled like try (but simpler since it can only have a single __except
or __finally), __except is fairly similar to catch (but simpler, since it can't
contain declarations). __leave is implemented similarly to break / continue.

Use the existing addTryDispatchBlock infrastructure (which
FindUnreachableCode() in ReachableCode.cpp uses via cfg->try_blocks_begin()) to
mark things in the __except blocks as reachable.

Re-use TryTerminatedBlock. This means we add EH edges from calls to the __try
block, but not from all other statements. While this is incomplete, it matches
LLVM's SEH codegen support. Also, in practice, BuildOpts.AddEHEdges is always
false in practice from what I can tell, so we never even insert the call EH
edges either.

https://reviews.llvm.org/D36914


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@311561 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 55 insertions, 0 deletions

diff --git a/test/Sema/warn-unreachable-ms.c b/test/Sema/warn-unreachable-ms.c
new file mode 100644
index 0000000000..421415e932
--- /dev/null
+++ b/test/Sema/warn-unreachable-ms.c
@@ -0,0 +1,55 @@
+// RUN: %clang_cc1 %s -triple=i686-pc-win32 -fsyntax-only -verify -fms-extensions -Wunreachable-code
+
+void f();
+
+void g1() {
+  __try {
+    f();
+    __leave;
+    f();  // expected-warning{{will never be executed}}
+  } __except(1) {
+    f();
+  }
+
+  // Completely empty.
+  __try {
+  } __except(1) {
+  }
+
+  __try {
+    f();
+    return;
+  } __except(1) {  // Filter expression should not be marked as unreachable.
+    // Empty __except body.
+  }
+}
+
+void g2() {
+  __try {
+    // Nested __try.
+    __try {
+      f();
+      __leave;
+      f(); // expected-warning{{will never be executed}}
+    } __except(2) {
+    }
+    f();
+    __leave;
+    f(); // expected-warning{{will never be executed}}
+  } __except(1) {
+    f();
+  }
+}
+
+void g3() {
+  __try {
+    __try {
+      f();
+    } __except (1) {
+      __leave; // should exit outer try
+    }
+    __leave;
+    f(); // expected-warning{{never be executed}}
+  } __except (1) {
+  }
+}