Remove redundant decls

Pass through the closure set looking for Decls we can erase. For
example:
```
struct ll;

struct ll;

int get(struct ll *);

struct ll;
```
We just need the first `struct ll;`

Signed-off-by: Giuliano Belinassi <[email protected]>

libcextract/FunctionDepsFinder.cpp

@@ -57,8 +57,10 @@ void FunctionDependencyFinder::Remove_Redundant_Decls(void)
 {
   ClosureSet &closure = Visitor.Get_Closure();
   std::unordered_set<Decl *> &closure_set = closure.Get_Set();
+  bool inc;
 
-  for (auto it = closure_set.begin(); it != closure_set.end(); ++it) {
+  for (auto it = closure_set.begin(); it != closure_set.end(); inc ? ++it : it) {
+    inc = true;
     /* Handle the case where a enum or struct is declared as:
 
         typedef enum Hand {
@@ -198,9 +200,27 @@ void FunctionDependencyFinder::Remove_Redundant_Decls(void)
         }
       }
     }
+
+    /* Try to remove any decls in the main file which are
+       redundant, which means that have equivalent previous decl.  */
+    Decl *decl = *it;
+
+    if (AST->isInMainFileID(decl->getBeginLoc()) &&
+        AST->isInMainFileID(decl->getEndLoc())) {
+
+      for (Decl *prev = decl->getPreviousDecl();
+           prev != nullptr;
+           prev = prev->getPreviousDecl()) {
+        if (closure.Is_Decl_Marked(prev) && Is_Decl_Equivalent_To(decl, prev)) {
+          ++it;
+          inc = false;
+          closure.Remove_Decl(decl);
+          break;
+        }
+      }
+    }
   }
 
-  // FIXME: use interval tree
   ASTUnit::top_level_iterator it;
   Decl *prev = nullptr;
   for (it = AST->top_level_begin(); it != AST->top_level_end(); ++it) {

libcextract/LLVMMisc.cpp

@@ -281,3 +281,22 @@ DeclContextLookupResult Get_Decl_From_Symtab(ASTUnit *ast, const StringRef &name
 
   return Get_Decl_From_Symtab(ast, info->getValue());
 }
+
+/** Check if two Decls are equivalent.  */
+bool Is_Decl_Equivalent_To(Decl *a, Decl *b)
+{
+  std::string a_str;
+  std::string b_str;
+
+  llvm::raw_string_ostream a_stream(a_str);
+  llvm::raw_string_ostream b_stream(b_str);
+
+  a->print(a_stream);
+  b->print(b_stream);
+
+  if (a_str == b_str) {
+    return true;
+  }
+
+  return false;
+}

libcextract/LLVMMisc.hh

@@ -100,3 +100,6 @@ DeclContextLookupResult Get_Decl_From_Symtab(ASTUnit *ast, const IdentifierInfo
 
 /** Lookup in the symbol table for a declaration with given name passed by name.  */
 DeclContextLookupResult Get_Decl_From_Symtab(ASTUnit *ast, const StringRef &name);
+
+/** Check if two Decls are equivalent.  */
+bool Is_Decl_Equivalent_To(Decl *a, Decl *b);

testsuite/small/redundant-1.c

@@ -0,0 +1,16 @@
+/* { dg-options "-DCE_EXTRACT_FUNCTIONS=f -DCE_NO_EXTERNALIZATION" }*/
+
+struct ll;
+
+struct ll;
+
+int get(struct ll *);
+
+struct ll;
+
+int f(struct ll *l)
+{
+  return get(l);
+}
+
+/* { dg-final { scan-tree-dump-not "struct ll;\n+int get\(struct ll \*\);" } } */