[Coverage] Precise region termination with deferred regions

The current coverage implementation doesn't handle region termination
very precisely. Take for example an `if' statement with a `return':

  void f() {
    if (true) {
      return; // The `if' body's region is terminated here.
    }
    // This line gets the same coverage as the `if' condition.
  }

If the function `f' is called, the line containing the comment will be
marked as having executed once, which is not correct.

The solution here is to create a deferred region after terminating a
region. The deferred region is completed once the start location of the
next statement is known, and is then pushed onto the region stack.
In the cases where it's not possible to complete a deferred region, it
can safely be dropped.

Testing: lit test updates, a stage2 coverage-enabled build of clang
llvm-svn: 310010
diff --git a/clang/test/CoverageMapping/label.cpp b/clang/test/CoverageMapping/label.cpp
index 1c5111a6..aec5e4f 100644
--- a/clang/test/CoverageMapping/label.cpp
+++ b/clang/test/CoverageMapping/label.cpp
@@ -14,19 +14,22 @@
       int m = 2;
     } else
       goto x;                // CHECK-NEXT: File 0, [[@LINE]]:7 -> [[@LINE]]:13 = (#1 - #2)
-    int k = 3;               // CHECK-NEXT: File 0, [[@LINE]]:5 -> [[@LINE+1]]:4 = #3
-  }
-  static int j = 0;          // CHECK-NEXT: File 0, [[@LINE]]:3 -> [[@LINE+4]]:2 = ((#0 + #3) - #1)
+    int k = 3;               // CHECK-NEXT: File 0, [[@LINE-1]]:13 -> [[@LINE]]:5 = #3
+  }                          // CHECK-NEXT: File 0, [[@LINE-1]]:5 -> [[@LINE]]:4 = #3
+  static int j = 0;          // CHECK-NEXT: File 0, [[@LINE]]:3 -> [[@LINE+5]]:2 = ((#0 + #3) - #1)
   ++j;
   if(j == 1)                 // CHECK-NEXT: File 0, [[@LINE]]:6 -> [[@LINE]]:12 = ((#0 + #3) - #1)
     goto x;                  // CHECK-NEXT: File 0, [[@LINE]]:5 -> [[@LINE]]:11 = #4
+                             // CHECK-NEXT: File 0, [[@LINE-1]]:11 -> [[@LINE+1]]:2 = (((#0 + #3) - #1) - #4)
 }
 
                              // CHECK-NEXT: test1
 void test1(int x) {          // CHECK-NEXT: File 0, [[@LINE]]:19 -> {{[0-9]+}}:2 = #0
   if(x == 0)                 // CHECK-NEXT: File 0, [[@LINE]]:6 -> [[@LINE]]:12 = #0
     goto a;                  // CHECK-NEXT: File 0, [[@LINE]]:5 -> [[@LINE]]:11 = #1
-  goto b;                    // CHECK-NEXT: File 0, [[@LINE]]:3 -> [[@LINE]]:9 = (#0 - #1)
+                             // CHECK-NEXT: File 0, [[@LINE-1]]:11 -> [[@LINE+1]]:3 = (#0 - #1)
+  goto b;                    // CHECK-NEXT: File 0, [[@LINE]]:3 -> [[@LINE+5]]:2 = (#0 - #1)
+                             // CHECK-NEXT: File 0, [[@LINE-1]]:3 -> [[@LINE+4]]:2 = #3
 a:                           // CHECK-NEXT: File 0, [[@LINE]]:1 -> [[@LINE+3]]:2 = #2
 b:                           // CHECK-NEXT: File 0, [[@LINE]]:1 -> [[@LINE+2]]:2 = #3
   x = x + 1;
@@ -36,9 +39,11 @@
 void test2(int x) {          // CHECK-NEXT: File 0, [[@LINE]]:19 -> {{[0-9]+}}:2 = #0
   if(x == 0)                 // CHECK-NEXT: File 0, [[@LINE]]:6 -> [[@LINE]]:12 = #0
     goto a;                  // CHECK-NEXT: File 0, [[@LINE]]:5 -> [[@LINE]]:11 = #1
-                             // CHECK-NEXT: File 0, [[@LINE+2]]:8 -> [[@LINE+2]]:25 = (#0 - #1)
+                             // CHECK-NEXT: File 0, [[@LINE-1]]:11 -> [[@LINE+3]]:8 = #0
+                             // CHECK-NEXT: File 0, [[@LINE+2]]:8 -> [[@LINE+3]]:11 = (#0 - #1)
                              // CHECK-NEXT: File 0, [[@LINE+1]]:11 -> [[@LINE+1]]:17 = (#0 - #1)
-  else if(x == 1) goto b;    // CHECK-NEXT: File 0, [[@LINE]]:19 -> [[@LINE]]:25 = #2
+  else if(x == 1)            // CHECK-NEXT: File 0, [[@LINE+1]]:5 -> [[@LINE+1]]:11 = #2
+    goto b;                  // CHECK-NEXT: File 0, [[@LINE]]:11 -> [[@LINE+1]]:1 = #3
 a:                           // CHECK-NEXT: File 0, [[@LINE]]:1 -> [[@LINE+3]]:2 = #3
 b:                           // CHECK-NEXT: File 0, [[@LINE]]:1 -> [[@LINE+2]]:2 = #4
   x = x + 1;
@@ -47,11 +52,13 @@
                              // CHECK-NEXT: main
 int main() {                 // CHECK-NEXT: File 0, [[@LINE]]:12 -> {{[0-9]+}}:2 = #0
   int j = 0;
-  for(int i = 0; i < 10; ++i) { // CHECK: File 0, [[@LINE]]:31 -> [[@LINE+11]]:4 = #1
-  a:                         // CHECK-NEXT: File 0, [[@LINE]]:3 -> [[@LINE+10]]:4 = #2
+  for(int i = 0; i < 10; ++i) { // CHECK: File 0, [[@LINE]]:31 -> [[@LINE+13]]:4 = #1
+  a:                         // CHECK-NEXT: File 0, [[@LINE]]:3 -> [[@LINE+12]]:4 = #2
     if(i < 3)                // CHECK-NEXT: File 0, [[@LINE]]:8 -> [[@LINE]]:13 = #2
       goto e;                // CHECK-NEXT: File 0, [[@LINE]]:7 -> [[@LINE]]:13 = #3
-    goto c;                  // CHECK-NEXT: File 0, [[@LINE]]:5 -> [[@LINE]]:11 = (#2 - #3)
+                             // CHECK-NEXT: File 0, [[@LINE-1]]:13 -> [[@LINE+1]]:5 = (#2 - #3)
+    goto c;                  // CHECK-NEXT: File 0, [[@LINE]]:5 -> [[@LINE+8]]:4 = (#2 - #3)
+
   b:                         // CHECK-NEXT: File 0, [[@LINE]]:3 -> [[@LINE+6]]:4 = #4
     j = 2;
   c:                         // CHECK-NEXT: File 0, [[@LINE]]:3 -> [[@LINE+4]]:4 = #5