[analyzer][NFC] Refactor AnalysisConsumer::getModeForDecl()

[steakhal]

Summary

I just read this part of the code, and I found the nested ifs less readable.

[steakhal]

I should note that I compared this on multiple projects to the baseline version and no runtime nor reports changed.
So, this is purely a cosmetic change.

[martong]

LGTM!

[ASDenysPetrov]

clang/lib/StaticAnalyzer/Frontend/AnalysisConsumer.cpp

599–603

Why don't just leave this snippet as it was but add const SourceLocation Loc instead of re-assigning SL? Your construction made me stumbled for a while. As this patch is meant to bring readability, I wouldn't like to see such a code-trick. I see your intention to hide SL but IMO let compiler do this for us. See suggested.

[steakhal]

clang/lib/StaticAnalyzer/Frontend/AnalysisConsumer.cpp

599–603

Hm, you are probably right. The main idea was to reduce the number of unrelated declarations in the scope by nesting them into the calculation of the important ones.
However, we could relax in this case. I agree that would be even better.

clang/lib/StaticAnalyzer/Frontend/AnalysisConsumer.cpp

if (!Opts->AnalyzeSpecificFunction.empty() &&
       AnalysisDeclContext::getFunctionName(D) != Opts->AnalyzeSpecificFunction)
     return AM_None;
 
   // Unless -analyze-all is specified, treat decls differently depending on
   // where they came from:
   // - Main source file: run both path-sensitive and non-path-sensitive checks.
   // - Header files: run non-path-sensitive checks only.
   // - System headers: don't run any checks.
-  SourceManager &SM = Ctx->getSourceManager();
+  if (Opts->AnalyzeAll)
+    return Mode;
+
+  const SourceManager &SM = Ctx->getSourceManager();
+
+  const SourceLocation Loc = [&SM](Decl *D) -> SourceLocation {
     const Stmt *Body = D->getBody();
     SourceLocation SL = Body ? Body->getBeginLoc() : D->getLocation();
-  SL = SM.getExpansionLoc(SL);
+    return SM.getExpansionLoc(SL);
+  }(D);
 
-  if (!Opts->AnalyzeAll && !Mgr->isInCodeFile(SL)) {
-    if (SL.isInvalid() || SM.isInSystemHeader(SL))
-      return AM_None;
+  // Ignore system headers.
+  if (Loc.isInvalid() || SM.isInSystemHeader(Loc))
+
+  // Disable path sensitive analysis in user-headers.
+  if (!Mgr->isInCodeFile(Loc))
     return Mode & ~AM_Path;
-  }
 
   return Mode;
 }
 
 void AnalysisConsumer::HandleCode(Decl *D, AnalysisMode Mode,
                                   ExprEngine::InliningModes IMode,
                                   SetOfConstDecls *VisitedCallees) {
   if (!D->hasBody())