[sanitizer] Adjust code path of ChooseExternalSymbolizer for Windows

[yingcong-wu]

Summary

If path is null, user_path must also be null. With the current code path, the message of explicitly disabling symbolizer will never be reported. This patch adjusts the if-else structure to make that message can be reported.

[cchen15]

LGTM.

[yingcong-wu]

Ping @vitalybuka, could you please review this patch?

[yingcong-wu]

Hi @MaskRay , could you please take a look at this patch and help land it?

[yingcong-wu]

Kindly ping @vitalybuka and @MaskRay.

[MaskRay]

[sanitizer] adjust if-else block structure to make code reachable

Thanks. I think [sanitizer] Adjust ChooseExternalSymbolizer for Windows may be more meaningful. The most significant code change is to provide a diagnostic when external_symbolizer_path= (empty). Removing an unreachable code path is a side effect.

Block2 is unreachable(user_path must not be null if want to go into block2, but that means path will never be null, which block1 will run, NOT going into block2). [...]

You can simplify this to: If path is null, user_path must also be null. ...

[yingcong-wu]

Thank @MaskRay for your comment, I have updated the description of the patch.

[MaskRay]

LG

[yingcong-wu]

Hi @MaskRay, I don't have commit access, could you please help commit this patch?

compiler-rt/lib/sanitizer_common/sanitizer_symbolizer_win.cpp

if (user_path && internal_strchr(user_path, '%')) {
     char *new_path = (char *)InternalAlloc(kMaxPathLength);
     SubstituteForFlagValue(user_path, new_path, kMaxPathLength);
     user_path = new_path;
   }
 
   const char *path =
       user_path ? user_path : FindPathToBinary("llvm-symbolizer.exe");
   if (path) {
+    if (user_path && user_path[0] == '\0') {
+      VReport(2, "External symbolizer is explicitly disabled.\n");
+    } else {
       VReport(2, "Using llvm-symbolizer at %spath: %s\n",
               user_path ? "user-specified " : "", path);
-    list->push_back(new(*allocator) LLVMSymbolizer(path, allocator));
-  } else {
-    if (user_path && user_path[0] == '\0') {
-      VReport(2, "External symbolizer is explicitly disabled.\n");
-    } else {
-      VReport(2, "External symbolizer is not present.\n");
-    }
-  }
+      list->push_back(new (*allocator) LLVMSymbolizer(path, allocator));
+    }
 
   // Add the dbghelp based symbolizer.
   list->push_back(new(*allocator) WinSymbolizerTool());
 }
 
 Symbolizer *Symbolizer::PlatformInit() {
   IntrusiveList<SymbolizerTool> list;
   list.clear();