[clang] [Clang] Optimize some `getBeginLoc` implementations (PR #141058)

[Aaron Ballman via cfe-commits]

================
@@ -1510,41 +1519,41 @@ CallExpr *CallExpr::Create(const ASTContext &Ctx, Expr *Fn,
   unsigned NumArgs = std::max<unsigned>(Args.size(), MinNumArgs);
   unsigned SizeOfTrailingObjects = CallExpr::sizeOfTrailingObjects(
       /*NumPreArgs=*/0, NumArgs, FPFeatures.requiresTrailingStorage());
-  void *Mem =
-      Ctx.Allocate(sizeof(CallExpr) + SizeOfTrailingObjects, alignof(CallExpr));
-  return new (Mem) CallExpr(CallExprClass, Fn, /*PreArgs=*/{}, Args, Ty, VK,
-                            RParenLoc, FPFeatures, MinNumArgs, UsesADL);
+  void *Mem = Ctx.Allocate(
+      sizeToAllocateForCallExprSubclass<CallExpr>(SizeOfTrailingObjects),
+      alignof(CallExpr));
+  CallExpr *E =
+      new (Mem) CallExpr(CallExprClass, Fn, /*PreArgs=*/{}, Args, Ty, VK,
+                         RParenLoc, FPFeatures, MinNumArgs, UsesADL);
+  E->updateTrailingSourceLocs();
+  return E;
 }
 
 CallExpr *CallExpr::CreateEmpty(const ASTContext &Ctx, unsigned NumArgs,
                                 bool HasFPFeatures, EmptyShell Empty) {
   unsigned SizeOfTrailingObjects =
       CallExpr::sizeOfTrailingObjects(/*NumPreArgs=*/0, NumArgs, HasFPFeatures);
-  void *Mem =
-      Ctx.Allocate(sizeof(CallExpr) + SizeOfTrailingObjects, alignof(CallExpr));
+  void *Mem = Ctx.Allocate(
+      sizeToAllocateForCallExprSubclass<CallExpr>(SizeOfTrailingObjects),
+      alignof(CallExpr));
   return new (Mem)
       CallExpr(CallExprClass, /*NumPreArgs=*/0, NumArgs, HasFPFeatures, Empty);
 }
 
-unsigned CallExpr::offsetToTrailingObjects(StmtClass SC) {
-  switch (SC) {
-  case CallExprClass:
-    return sizeof(CallExpr);
-  case CXXOperatorCallExprClass:
-    return sizeof(CXXOperatorCallExpr);
-  case CXXMemberCallExprClass:
-    return sizeof(CXXMemberCallExpr);
-  case UserDefinedLiteralClass:
-    return sizeof(UserDefinedLiteral);
-  case CUDAKernelCallExprClass:
-    return sizeof(CUDAKernelCallExpr);
-  default:
-    llvm_unreachable("unexpected class deriving from CallExpr!");
-  }
-}
-
 Decl *Expr::getReferencedDeclOfCallee() {
-  Expr *CEE = IgnoreParenImpCasts();
+
+  // Optimize for the common case first
+  // (simple function or member function call)
+  // then try more exotic possibilities
+  Expr *CEE = IgnoreImpCasts();
+
+  if (auto *DRE = dyn_cast<DeclRefExpr>(CEE))
+    return DRE->getDecl();
+
+  if (auto *ME = dyn_cast<MemberExpr>(CEE))
+    return ME->getMemberDecl();
+
+  CEE = CEE->IgnoreParens();
----------------
AaronBallman wrote:

Warning bells going off!

>From `IgnoreParenImpCasts()`:
```
  /// Skip past any parentheses and implicit casts which might surround this
  /// expression until reaching a fixed point.
  /// FIXME: IgnoreParenImpCasts really ought to be equivalent to
  /// IgnoreParens() + IgnoreImpCasts() until reaching a fixed point. However
  /// this is currently not the case. Instead IgnoreParenImpCasts() skips:
```
Are we subtly changing behavior here?

https://github.com/llvm/llvm-project/pull/141058