[clang] d6acd01 - [Sema] Fix crash when evaluating nested call with value-dependent arg

[Pierre van Houtryve via cfe-commits]

Author: Pierre van Houtryve
Date: 2023-01-06T02:57:50-05:00
New Revision: d6acd0196b3378bdeb5193053e290d7194c4f72d

URL: https://github.com/llvm/llvm-project/commit/d6acd0196b3378bdeb5193053e290d7194c4f72d
DIFF: https://github.com/llvm/llvm-project/commit/d6acd0196b3378bdeb5193053e290d7194c4f72d.diff

LOG: [Sema] Fix crash when evaluating nested call with value-dependent arg

Fix an edge case `ExprConstant.cpp`'s `EvaluateWithSubstitution` when called by `CheckEnableIf`

The assertion in `CallStackFrame::getTemporary`
could fail during evaluation of nested calls to a function
using `enable_if` when the second argument was a
value-dependent expression.

This caused a temporary to be created for the second
argument with a given version during the
evaluation of the inner call, but we bailed out
when evaluating the second argument of the
outer call due to the expression being value-dependent.
After bailing out, we tried to clean up the argument's value slot but it
caused an assertion to trigger in `getTemporary` as
a temporary for the second argument existed, but only for the inner call and not the outer call.

See the test case for a more complete description of the issue.

Reviewed By: ahatanak

Differential Revision: https://reviews.llvm.org/D139713

Added: 
    clang/test/SemaCXX/enable_if-nested-call-with-valuedependent-param.cpp

Modified: 
    clang/lib/AST/ExprConstant.cpp

Removed: 
    


################################################################################
diff  --git a/clang/lib/AST/ExprConstant.cpp b/clang/lib/AST/ExprConstant.cpp
index 78cfecbec9fd3..a43845e53c5d0 100644
--- a/clang/lib/AST/ExprConstant.cpp
+++ b/clang/lib/AST/ExprConstant.cpp
@@ -594,11 +594,6 @@ namespace {
       auto LB = Temporaries.lower_bound(KV);
       if (LB != Temporaries.end() && LB->first == KV)
         return &LB->second;
-      // Pair (Key,Version) wasn't found in the map. Check that no elements
-      // in the map have 'Key' as their key.
-      assert((LB == Temporaries.end() || LB->first.first != Key) &&
-             (LB == Temporaries.begin() || std::prev(LB)->first.first != Key) &&
-             "Element with key 'Key' found in map");
       return nullptr;
     }
 

diff  --git a/clang/test/SemaCXX/enable_if-nested-call-with-valuedependent-param.cpp b/clang/test/SemaCXX/enable_if-nested-call-with-valuedependent-param.cpp
new file mode 100644
index 0000000000000..998f2ccf92534
--- /dev/null
+++ b/clang/test/SemaCXX/enable_if-nested-call-with-valuedependent-param.cpp
@@ -0,0 +1,44 @@
+// RUN: %clang_cc1 -fsyntax-only %s -std=c++14
+
+// Checks that Clang doesn't crash/assert on the nested call to "kaboom"
+// in "bar()".
+//
+// This is an interesting test case for `ExprConstant.cpp`'s `CallStackFrame`
+// because it triggers the following chain of events:
+// 0. `CheckEnableIf` calls `EvaluateWithSubstitution`.
+//  1. The outer call to "kaboom" gets evaluated.
+//   2. The expr for "a" gets evaluated, it has a version X;
+//      a temporary with the key (a, X) is created.
+//     3. The inner call to "kaboom" gets evaluated.
+//       4. The expr for "a" gets evaluated, it has a version Y;
+//          a temporary with the key (a, Y) is created.
+//       5. The expr for "b" gets evaluated, it has a version Y;
+//          a temporary with the key (b, Y) is created.
+//   6. `EvaluateWithSubstitution` looks at "b" but cannot evaluate it
+//      because it's value-dependent (due to the call to "f.foo()").
+//
+// When `EvaluateWithSubstitution` bails out while evaluating the outer
+// call, it attempts to fetch "b"'s param slot to clean it up.
+//
+// This used to cause an assertion failure in `getTemporary` because
+// a temporary with the key "(b, Y)" (created at step 4) existed but
+// not one for "(b, X)", which is what it was trying to fetch.
+
+template<typename T>
+__attribute__((enable_if(true, "")))
+T kaboom(T a, T b) {
+  return b;
+}
+
+struct A {
+  double foo();
+};
+
+template <int>
+struct B {
+  A &f;
+
+  void bar() {
+    kaboom(kaboom(0.0, 1.0), f.foo());
+  }
+};