Merge and improve code that detects same value in comparisons.

-Wtautological-overlap-compare and self-comparison from -Wtautological-compare
relay on detecting the same operand in different locations.  Previously, each
warning had it's own operand checker.  Now, both are merged together into
one function that each can call.  The function also now looks through member
access and array accesses.

Differential Revision: https://reviews.llvm.org/D66045


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@372453 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 105 insertions, 0 deletions

diff --git a/lib/AST/Expr.cpp b/lib/AST/Expr.cpp
index 00c6a81704..b5fb7fafb0 100644
--- a/lib/AST/Expr.cpp
+++ b/lib/AST/Expr.cpp
@@ -3921,6 +3921,111 @@ bool Expr::refersToGlobalRegisterVar() const {
   return false;
 }
 
+bool Expr::isSameComparisonOperand(const Expr* E1, const Expr* E2) {
+  E1 = E1->IgnoreParens();
+  E2 = E2->IgnoreParens();
+
+  if (E1->getStmtClass() != E2->getStmtClass())
+    return false;
+
+  switch (E1->getStmtClass()) {
+    default:
+      return false;
+    case CXXThisExprClass:
+      return true;
+    case DeclRefExprClass: {
+      // DeclRefExpr without an ImplicitCastExpr can happen for integral
+      // template parameters.
+      const auto *DRE1 = cast<DeclRefExpr>(E1);
+      const auto *DRE2 = cast<DeclRefExpr>(E2);
+      return DRE1->isRValue() && DRE2->isRValue() &&
+             DRE1->getDecl() == DRE2->getDecl();
+    }
+    case ImplicitCastExprClass: {
+      // Peel off implicit casts.
+      while (true) {
+        const auto *ICE1 = dyn_cast<ImplicitCastExpr>(E1);
+        const auto *ICE2 = dyn_cast<ImplicitCastExpr>(E2);
+        if (!ICE1 || !ICE2)
+          return false;
+        if (ICE1->getCastKind() != ICE2->getCastKind())
+          return false;
+        E1 = ICE1->getSubExpr()->IgnoreParens();
+        E2 = ICE2->getSubExpr()->IgnoreParens();
+        // The final cast must be one of these types.
+        if (ICE1->getCastKind() == CK_LValueToRValue ||
+            ICE1->getCastKind() == CK_ArrayToPointerDecay ||
+            ICE1->getCastKind() == CK_FunctionToPointerDecay) {
+          break;
+        }
+      }
+
+      const auto *DRE1 = dyn_cast<DeclRefExpr>(E1);
+      const auto *DRE2 = dyn_cast<DeclRefExpr>(E2);
+      if (DRE1 && DRE2)
+        return declaresSameEntity(DRE1->getDecl(), DRE2->getDecl());
+
+      const auto *Ivar1 = dyn_cast<ObjCIvarRefExpr>(E1);
+      const auto *Ivar2 = dyn_cast<ObjCIvarRefExpr>(E2);
+      if (Ivar1 && Ivar2) {
+        return Ivar1->isFreeIvar() && Ivar2->isFreeIvar() &&
+               declaresSameEntity(Ivar1->getDecl(), Ivar2->getDecl());
+      }
+
+      const auto *Array1 = dyn_cast<ArraySubscriptExpr>(E1);
+      const auto *Array2 = dyn_cast<ArraySubscriptExpr>(E2);
+      if (Array1 && Array2) {
+        if (!isSameComparisonOperand(Array1->getBase(), Array2->getBase()))
+          return false;
+
+        auto Idx1 = Array1->getIdx();
+        auto Idx2 = Array2->getIdx();
+        const auto Integer1 = dyn_cast<IntegerLiteral>(Idx1);
+        const auto Integer2 = dyn_cast<IntegerLiteral>(Idx2);
+        if (Integer1 && Integer2) {
+          if (Integer1->getValue() != Integer2->getValue())
+            return false;
+        } else {
+          if (!isSameComparisonOperand(Idx1, Idx2))
+            return false;
+        }
+
+        return true;
+      }
+
+      // Walk the MemberExpr chain.
+      while (isa<MemberExpr>(E1) && isa<MemberExpr>(E2)) {
+        const auto *ME1 = cast<MemberExpr>(E1);
+        const auto *ME2 = cast<MemberExpr>(E2);
+        if (!declaresSameEntity(ME1->getMemberDecl(), ME2->getMemberDecl()))
+          return false;
+        if (const auto *D = dyn_cast<VarDecl>(ME1->getMemberDecl()))
+          if (D->isStaticDataMember())
+            return true;
+        E1 = ME1->getBase()->IgnoreParenImpCasts();
+        E2 = ME2->getBase()->IgnoreParenImpCasts();
+      }
+
+      if (isa<CXXThisExpr>(E1) && isa<CXXThisExpr>(E2))
+        return true;
+
+      // A static member variable can end the MemberExpr chain with either
+      // a MemberExpr or a DeclRefExpr.
+      auto getAnyDecl = [](const Expr *E) -> const ValueDecl * {
+        if (const auto *DRE = dyn_cast<DeclRefExpr>(E))
+          return DRE->getDecl();
+        if (const auto *ME = dyn_cast<MemberExpr>(E))
+          return ME->getMemberDecl();
+        return nullptr;
+      };
+
+      const ValueDecl *VD1 = getAnyDecl(E1);
+      const ValueDecl *VD2 = getAnyDecl(E2);
+      return declaresSameEntity(VD1, VD2);
+    }
+  }
+}
+
 /// isArrow - Return true if the base expression is a pointer to vector,
 /// return false if the base expression is a vector.
 bool ExtVectorElementExpr::isArrow() const {