[Clang] Only check exprs that might be immediate escalating in evaluated contexts

[cor3ntin]

As per https://eel.is/c++draft/expr.const#17

Fixes #91308

[llvmbot]

@llvm/pr-subscribers-clang

Author: cor3ntin (cor3ntin)

Changes

As per https://eel.is/c++draft/expr.const#17

Fixes #91308

---

Full diff: https://github.com/llvm/llvm-project/pull/93187.diff

4 Files Affected:

• (modified) clang/docs/ReleaseNotes.rst (+2)
• (modified) clang/include/clang/Sema/Sema.h (+13)
• (modified) clang/lib/Sema/SemaTemplateDeduction.cpp (+5)
• (modified) clang/test/SemaCXX/cxx2b-consteval-propagate.cpp (+8)

diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 0c4a343b70009..55b963657a1d7 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -769,6 +769,8 @@ Bug Fixes to C++ Support
 - Fixed a crash when trying to emit captures in a lambda call operator with an explicit object
   parameter that is called on a derived type of the lambda.
   Fixes (#GH87210), (GH89541).
+- Clang no longer try to check if an expression is immediate-escalating in an unevaluated context.
+  Fixes (#GH91308).
 
 Bug Fixes to AST Handling
 ^^^^^^^^^^^^^^^^^^^^^^^^^
diff --git a/clang/include/clang/Sema/Sema.h b/clang/include/clang/Sema/Sema.h
index 057ff61ccc644..8888bf3923823 100644
--- a/clang/include/clang/Sema/Sema.h
+++ b/clang/include/clang/Sema/Sema.h
@@ -5112,6 +5112,13 @@ class Sema final : public SemaBase {
              Context == ExpressionEvaluationContext::UnevaluatedList;
     }
 
+    bool isPotentiallyEvaluated() const {
+      return Context == ExpressionEvaluationContext::PotentiallyEvaluated ||
+             Context ==
+                 ExpressionEvaluationContext::PotentiallyEvaluatedIfUsed ||
+             Context == ExpressionEvaluationContext::ConstantEvaluated;
+    }
+
     bool isConstantEvaluated() const {
       return Context == ExpressionEvaluationContext::ConstantEvaluated ||
              Context == ExpressionEvaluationContext::ImmediateFunctionContext;
@@ -5146,6 +5153,12 @@ class Sema final : public SemaBase {
     return ExprEvalContexts.back();
   };
 
+  const ExpressionEvaluationContextRecord &parentEvaluationContext() const {
+    assert(ExprEvalContexts.size() >= 2 &&
+           "Must be in an expression evaluation context");
+    return ExprEvalContexts[ExprEvalContexts.size() - 2];
+  };
+
   bool isBoundsAttrContext() const {
     return ExprEvalContexts.back().ExprContext ==
            ExpressionEvaluationContextRecord::ExpressionKind::
diff --git a/clang/lib/Sema/SemaTemplateDeduction.cpp b/clang/lib/Sema/SemaTemplateDeduction.cpp
index 76f47e9cb2560..08a69d3cb2589 100644
--- a/clang/lib/Sema/SemaTemplateDeduction.cpp
+++ b/clang/lib/Sema/SemaTemplateDeduction.cpp
@@ -4788,8 +4788,13 @@ TemplateDeductionResult Sema::DeduceTemplateArguments(
       DeduceReturnType(Specialization, Info.getLocation(), false))
     return TemplateDeductionResult::MiscellaneousDeductionFailure;
 
+  // [C++26][expr.const]/p17
+  // An expression or conversion is immediate-escalating if it is not initially
+  // in an immediate function context and it is [...]
+  // a potentially-evaluated id-expression that denotes an immediate function.
   if (IsAddressOfFunction && getLangOpts().CPlusPlus20 &&
       Specialization->isImmediateEscalating() &&
+      parentEvaluationContext().isPotentiallyEvaluated() &&
       CheckIfFunctionSpecializationIsImmediate(Specialization,
                                                Info.getLocation()))
     return TemplateDeductionResult::MiscellaneousDeductionFailure;
diff --git a/clang/test/SemaCXX/cxx2b-consteval-propagate.cpp b/clang/test/SemaCXX/cxx2b-consteval-propagate.cpp
index 07937deb66738..b70c02201ac3c 100644
--- a/clang/test/SemaCXX/cxx2b-consteval-propagate.cpp
+++ b/clang/test/SemaCXX/cxx2b-consteval-propagate.cpp
@@ -446,3 +446,11 @@ int h(int x) {
 }
 
 #endif
+
+
+namespace GH91308 {
+    constexpr void f(auto) {
+        static_assert(false);
+    }
+    using R1 = decltype(&f<int>);
+}

[Fznamznon]

I can grep at least 4 places in clang/lib/sema where we do ExprEvalContexts.size() - 2. Would be a good first issue to switch these to parentEvaluationContext calls (once we merge this patch)?

[cor3ntin]

Yes, I was actually thinking of doing that!

[Fznamznon]

Submitted #93284

[AaronBallman]

LGTM