[Coverage] Restore the correct count value after processing a nested region in case of combined regions.

If several regions cover the same area of code, we have to restore
the combined value for that area when return from a nested region.

This patch achieves that by combining regions before calling buildSegments.

Differential Revision: http://reviews.llvm.org/D18610

llvm-svn: 267390
diff --git a/llvm/test/tools/llvm-cov/showTemplateInstantiations.cpp b/llvm/test/tools/llvm-cov/showTemplateInstantiations.cpp
index a9be473..ad00199 100644
--- a/llvm/test/tools/llvm-cov/showTemplateInstantiations.cpp
+++ b/llvm/test/tools/llvm-cov/showTemplateInstantiations.cpp
@@ -7,10 +7,10 @@
 int func(T x) {      // ALL-NEXT:    2| [[@LINE]]|int func(T x) {
   if(x)              // ALL-NEXT:    2| [[@LINE]]|  if(x)
     return 0;        // ALL-NEXT:    1| [[@LINE]]|    return 0;
-  else               // ALL-NEXT:    1| [[@LINE]]|  else
+  else               // ALL-NEXT:    2| [[@LINE]]|  else
     return 1;        // ALL-NEXT:    1| [[@LINE]]|    return 1;
   int j = 1;         // ALL-NEXT:    0| [[@LINE]]|  int j = 1;
-}                    // ALL-NEXT:    1| [[@LINE]]|}
+}                    // ALL-NEXT:    2| [[@LINE]]|}
 
                      // CHECK:       {{^ *(\| )?}}_Z4funcIbEiT_:
                      // CHECK-NEXT:  1| [[@LINE-9]]|int func(T x) {