[PATCH] D52957: [analyzer] Teach CallEvent about C++17 aligned new.

[Artem Dergachev via Phabricator via cfe-commits]

NoQ created this revision.
NoQ added reviewers: dcoughlin, xazax.hun, a.sidorin, george.karpenkov, szepet, rnkovacs.
Herald added subscribers: cfe-commits, Szelethus, mikhail.ramalho, baloghadamsoftware.

In C++17, when class `C` has large alignment value, a special case of overload resolution rule kicks in for expression `new C` that causes the aligned version of `operator new()` to be called. The aligned `new` has two arguments: size and alignment. However, the new-expression has only one argument: the construct-expression for `C()`. This causes a false positive in `core.CallAndMessage`'s check for matching number of arguments and number of parameters.

Update `CXXAllocatorCall`, which is a `CallEvent` sub-class for operator new calls within new-expressions, so that the number of arguments always matched the number of parameters.

Dunno, maybe we should instead abandon the idea of reserving a whole argument/parameter index for each of those implicit arguments that aren't even represented by an expression in the AST.

Side note: Ugh, we never supported passing size into `operator new()` calls, even though it's known in compile time. And now also alignment. They are currently symbolic (unconstrained) within allocator calls.


Repository:
  rC Clang

https://reviews.llvm.org/D52957

Files:
  include/clang/StaticAnalyzer/Core/PathSensitive/CallEvent.h
  lib/StaticAnalyzer/Core/CallEvent.cpp
  test/Analysis/new-aligned.cpp


Index: test/Analysis/new-aligned.cpp
===================================================================
--- /dev/null
+++ test/Analysis/new-aligned.cpp
@@ -0,0 +1,14 @@
+//RUN: %clang_analyze_cc1 -std=c++17 -analyze -analyzer-checker=core -verify %s
+
+// expected-no-diagnostics
+
+// Notice the weird alignment.
+struct alignas(1024) S {};
+
+void foo() {
+  // Operator new() here is the C++17 aligned new that takes two arguments:
+  // size and alignment. Size is passed implicitly as usual, and alignment
+  // is passed implicitly in a similar manner.
+  S *s = new S; // no-warning
+  delete s;
+}
Index: lib/StaticAnalyzer/Core/CallEvent.cpp
===================================================================
--- lib/StaticAnalyzer/Core/CallEvent.cpp
+++ lib/StaticAnalyzer/Core/CallEvent.cpp
@@ -503,10 +503,14 @@
     const ParmVarDecl *ParamDecl = *I;
     assert(ParamDecl && "Formal parameter has no decl?");
 
+    // TODO: Support allocator calls.
     if (Call.getKind() != CE_CXXAllocator)
       if (Call.isArgumentConstructedDirectly(Idx))
         continue;
 
+    // TODO: Allocators should receive the correct size and possibly alignment,
+    // determined in compile-time but not represented as arg-expressions,
+    // which makes getArgSVal() fail and return UnknownVal.
     SVal ArgVal = Call.getArgSVal(Idx);
     if (!ArgVal.isUnknown()) {
       Loc ParamLoc = SVB.makeLoc(MRMgr.getVarRegion(ParamDecl, CalleeCtx));
Index: include/clang/StaticAnalyzer/Core/PathSensitive/CallEvent.h
===================================================================
--- include/clang/StaticAnalyzer/Core/PathSensitive/CallEvent.h
+++ include/clang/StaticAnalyzer/Core/PathSensitive/CallEvent.h
@@ -921,15 +921,28 @@
     return getOriginExpr()->getOperatorNew();
   }
 
+  // Size and maybe implicit alignment in C++17. Instead of size, the AST
+  // contains the construct-expression. Alignment is always hidden.
+  // We pretend that argument 0 is size and argument 1 is alignment (if passed
+  // implicitly) and the rest are placement args. This makes sure that the
+  // number of arguments is always the same as the number of parameters.
+  unsigned getNumImplicitArgs() const {
+    return getOriginExpr()->passAlignment() ? 2 : 1;
+  }
+
   unsigned getNumArgs() const override {
-    return getOriginExpr()->getNumPlacementArgs() + 1;
+    return getOriginExpr()->getNumPlacementArgs() + getNumImplicitArgs();
   }
 
   const Expr *getArgExpr(unsigned Index) const override {
     // The first argument of an allocator call is the size of the allocation.
-    if (Index == 0)
+    if (Index < getNumImplicitArgs())
       return nullptr;
-    return getOriginExpr()->getPlacementArg(Index - 1);
+    return getOriginExpr()->getPlacementArg(Index - getNumImplicitArgs());
+  }
+
+  const Expr *getPlacementArgExpr(unsigned Index) const {
+    return getOriginExpr()->getPlacementArg(Index);
   }
 
   Kind getKind() const override { return CE_CXXAllocator; }


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