[clang] [Clang] Make the result type of sizeof/pointer subtraction/size_t literals be typedefs instead of built-in types (PR #143653)

[Matheus Izvekov via cfe-commits]

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@@ -320,6 +321,69 @@ bool clang::analyze_format_string::ParseUTF8InvalidSpecifier(
 // Methods on ArgType.
 //===----------------------------------------------------------------------===//
 
+static bool namedTypeToLengthModifierKind(QualType QT,
+                                          LengthModifier::Kind &K) {
+  for (/**/; const auto *TT = QT->getAs<TypedefType>();
+       QT = TT->getDecl()->getUnderlyingType()) {
+    StringRef Name = TT->getDecl()->getIdentifier()->getName();
+    if (Name == "size_t" || Name == "__size_t") {
+      K = LengthModifier::AsSizeT;
+      return true;
+    } else if (Name == "__signed_size_t" ||
+               Name == "ssize_t" /*Not C99, but common in Unix.*/) {
+      K = LengthModifier::AsSizeT;
+      return true;
+    } else if (Name == "ptrdiff_t" || Name == "__ptrdiff_t") {
+      K = LengthModifier::AsPtrDiff;
+      return true;
+    } else if (Name == "intmax_t") {
+      K = LengthModifier::AsIntMax;
+      return true;
+    } else if (Name == "uintmax_t") {
+      K = LengthModifier::AsIntMax;
+      return true;
+    }
+  }
+  return false;
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mizvekov wrote:

I understand, but this will still match a user defined size_t in an arbitrary namespace, which looks suspicious.

I think this should check these typedefs are in the correct scope, and also this probably should be restricted to the implicit stuff, in -ffreestanding mode.

https://github.com/llvm/llvm-project/pull/143653