[analyzer] Utility to extract the variable name from a memory region.

[xazax.hun]

Summary

This patch adds a small utility to extract variable name from a memory region.
This patch does not contain any test or user yet.
There are however two differential revisions that needs similar functionality. It would be great to decide what implementation to use and make it available as a general utility.

The two potential users: http://reviews.llvm.org/D12761 and http://reviews.llvm.org/D15227

[Alexander_Droste]

lib/StaticAnalyzer/Core/MemRegion.cpp

586

Isn't calling getDecl() and getName() afterwards identical to printPretty()?
Is it possible that a NamedDecl cannot be obtained from a DeclRegion?

588

Regarding the MPI-Checker patch http://reviews.llvm.org/D12761 it is insufficient
if the array index (if obtainable) is not provided.
I think it would be nice if a getVariableName function could always provide as much
information as possible, regarding the passed memory region. Do you actually see a case in
the other implementation where this function fails?
The index is a member variable of the ElementRegion why obtaining that
value cannot fail. If the memory region passed is no ElementRegion then
simply printPretty() is called. I could submit the patch right away if this helps.

[xazax.hun]

lib/StaticAnalyzer/Core/MemRegion.cpp

586

The printPretty function copy the name of the variable. First I wanted to avoid any copy and memory allocation, but I realized this utility will probably only be used for diagnostics which is the exceptional case, I think allocations should not cause any performance problem here.

But you are right printPretty is almost identical except for FieldRegions, where it also try to print the super region.
I checked and DeclRegion has 3 superclasses, all of them should contain NamedDecls, so that check should never fail.

588

In this case I think you should commit your version.

include/clang/StaticAnalyzer/Core/PathSensitive/MemRegion.h

public:
 
   /// \brief Print the region for use in diagnostics.
   virtual void printPretty(raw_ostream &os) const;
 
   /// \brief Returns true if this region's textual representation can be used
   /// as part of a larger expression.
   virtual bool canPrintPrettyAsExpr() const;
 
+  /// \brief In case this region is a region of a variable or an element region,
+  /// this method will return the name of the variable. Otherwise it will return
+  /// an empty StringRef.
+  StringRef getVariableName() const;
+
   /// \brief Print the region as expression.
   ///
   /// When this region represents a subexpression, the method is for printing
   /// an expression containing it.
   virtual void printPrettyAsExpr(raw_ostream &os) const;
 
   Kind getKind() const { return kind; }
 

lib/StaticAnalyzer/Core/MemRegion.cpp

 bool MemRegion::canPrintPretty() const {
   return canPrintPrettyAsExpr();
 }
 
 bool MemRegion::canPrintPrettyAsExpr() const {
   return false;
 }
 
+StringRef MemRegion::getVariableName() const {
+  const MemRegion *reg = this;
+  while (const auto *ereg = dyn_cast<ElementRegion>(reg))
+    reg = ereg->getSuperRegion();
+  const auto *vreg = dyn_cast<DeclRegion>(reg);
+  if (!vreg)
+    return "";
+  const auto *nd = dyn_cast<NamedDecl>(vreg->getDecl());
+  if (!nd)
+    return "";
+  return nd->getName();
+}
+
 void MemRegion::printPretty(raw_ostream &os) const {
   assert(canPrintPretty() && "This region cannot be printed pretty.");
   os << "'";
   printPrettyAsExpr(os);
   os << "'";
   return;
 }