[demangler] Improve ->* & .* demangling

The demangler treats ->* as a BinaryExpr, but .* as a MemberExpr.
That's inconsistent.  This makes the former a MemberExpr too.
However, in order to not regress the paren output, MemberExpr::print
is modified to parenthesize the MemberExpr if the operator ends with
'*'.  Printing is affected thusly:

Before:
    obj.member
    obj->member
    obj.*member
    (obj) ->* (member)

After:
   obj.member   # Unchanged
   obj->member  # Unchanged
   obj.*(member)  # Added paren member operand
   obj->*(member) # Removed paren on object operand, less whitespace

The right solution to the paren problem is to add some notion of
precedence (and associativity) to Nodes, but that's a larger change
that would become simpler once the refactoring I'm doing is completed.

FWIW, binutils' demangler's paren algorithm has a small idea of
precedence, and will generally not emit parens when the operand is
unary.

Reviewed By: bruno

Differential Revision: https://reviews.llvm.org/D118486

2 files changed, 17 insertions, 4 deletions

diff --git a/libcxxabi/src/demangle/ItaniumDemangle.h b/libcxxabi/src/demangle/ItaniumDemangle.h
index d0eaf6d66480..d79452e42ea2 100644
--- a/libcxxabi/src/demangle/ItaniumDemangle.h
+++ b/libcxxabi/src/demangle/ItaniumDemangle.h
@@ -1787,7 +1787,13 @@ public:
   void printLeft(OutputBuffer &OB) const override {
     LHS->print(OB);
     OB += Kind;
+    // Parenthesize pointer-to-member deference argument.
+    bool IsPtr = Kind.back() == '*';
+    if (IsPtr)
+      OB += '(';
     RHS->print(OB);
+    if (IsPtr)
+      OB += ')';
   }
 };
 
@@ -4847,9 +4853,16 @@ Node *AbstractManglingParser<Derived, Alloc>::parseExpr() {
     return nullptr;
   case 'p':
     switch (First[1]) {
-    case 'm':
+    case 'm': {
       First += 2;
-      return getDerived().parseBinaryExpr("->*");
+      Node *LHS = getDerived().parseExpr();
+      if (LHS == nullptr)
+        return LHS;
+      Node *RHS = getDerived().parseExpr();
+      if (RHS == nullptr)
+        return nullptr;
+      return make<MemberExpr>(LHS, "->*", RHS);
+    }
     case 'l':
       First += 2;
       return getDerived().parseBinaryExpr("+");
diff --git a/libcxxabi/test/test_demangle.pass.cpp b/libcxxabi/test/test_demangle.pass.cpp
index 263494af75d0..78289ffcfe2d 100644
--- a/libcxxabi/test/test_demangle.pass.cpp
+++ b/libcxxabi/test/test_demangle.pass.cpp
@@ -29481,7 +29481,7 @@ const char* cases[][2] =
     {"_ZN5Casts8implicitILj4EEEvPN9enable_ifIXooT_Li4EEvE4typeE", "void Casts::implicit<4u>(enable_if<(4u) || (4), void>::type*)"},
     {"_ZN5Casts8implicitILj4EEEvPN9enable_ifIXorT_Li4EEvE4typeE", "void Casts::implicit<4u>(enable_if<(4u) | (4), void>::type*)"},
     {"_ZN5Casts8implicitILj4EEEvPN9enable_ifIXoRT_Li4EEvE4typeE", "void Casts::implicit<4u>(enable_if<(4u) |= (4), void>::type*)"},
-    {"_ZN5Casts8implicitILj4EEEvPN9enable_ifIXpmT_Li4EEvE4typeE", "void Casts::implicit<4u>(enable_if<(4u) ->* (4), void>::type*)"},
+    {"_ZN5Casts8implicitILj4EEEvPN9enable_ifIXpmT_Li4EEvE4typeE", "void Casts::implicit<4u>(enable_if<4u->*(4), void>::type*)"},
     {"_ZN5Casts8implicitILj4EEEvPN9enable_ifIXplT_Li4EEvE4typeE", "void Casts::implicit<4u>(enable_if<(4u) + (4), void>::type*)"},
     {"_ZN5Casts8implicitILj4EEEvPN9enable_ifIXpLT_Li4EEvE4typeE", "void Casts::implicit<4u>(enable_if<(4u) += (4), void>::type*)"},
     {"_ZN5Casts8implicitILj4EEEvPN9enable_ifIXppT_EvE4typeE", "void Casts::implicit<4u>(enable_if<(4u)++, void>::type*)"},
@@ -29658,7 +29658,7 @@ const char* cases[][2] =
     {"_ZN5test21hIPFfvEEEvT_DTcvPFDTclfL0p_EEvELi0EE", "void test2::h<float (*)()>(float (*)(), decltype((decltype(fp()) (*)())(0)))"},
     {"_ZN5test21iIPFfvEEEvDTcvPFDTclfp_EET_ELi0EE", "void test2::i<float (*)()>(decltype((decltype(fp()) (*)(float (*)()))(0)))"},
     {"_ZZN5test21gIPFfvEEEvT_DTclfL0p_EEE8variable", "void test2::g<float (*)()>(float (*)(), decltype(fp()))::variable"},
-    {"_ZN5test31aINS_1XEMS1_PiEEvT_T0_DTdsfL0p_fL0p0_E", "void test3::a<test3::X, int* test3::X::*>(test3::X, int* test3::X::*, decltype(fp.*fp0))"},
+    {"_ZN5test31aINS_1XEMS1_PiEEvT_T0_DTdsfL0p_fL0p0_E", "void test3::a<test3::X, int* test3::X::*>(test3::X, int* test3::X::*, decltype(fp.*(fp0)))"},
     {"_ZN5test43tf1INS_1XEEEvDTnw_T_piLi1EEE", "void test4::tf1<test4::X>(decltype(new test4::X(1)))"},
     {"_ZN5test51aIiEEvDTnxcvT__EE", "void test5::a<int>(decltype(noexcept ((int)())))"},
     {"_ZN5test62f1IiEEvDTcvT_dtdtL_ZNS_1zEE2ua1iE", "void test6::f1<int>(decltype((int)(test6::z.ua.i)))"},