[clang] NFCI: don't check deduced constraints when partial ordering

[mizvekov]

We were incorrectly applying [temp.deduct]p5 to partial ordering.

Marked as NFCI as I don't think the difference is actually observable in practice.
During partial ordering, the deduced arguments will mostly be dependent and thus cannot be checked.
Otherwise, later during overload resolution, if deduction succeeds in both directions,
we will perform subsumption check for the constraints ([temp.func.order]p6).

[llvmbot]

@llvm/pr-subscribers-clang

Author: Matheus Izvekov (mizvekov)

Changes

We were incorrectly applying [temp.deduct]p5 to partial ordering.

Marked as NFCI as I don't think the difference is actually observable in practice.
During partial ordering, the deduced arguments will mostly be dependent and thus cannot be checked.
Otherwise, later during overload resolution, if deduction succeeds in both directions,
we will perform subsumption check for the constraints ([temp.func.order]p6).

---

Full diff: https://github.com/llvm/llvm-project/pull/106882.diff

1 Files Affected:

• (modified) clang/lib/Sema/SemaTemplateDeduction.cpp (+15-21)

diff --git a/clang/lib/Sema/SemaTemplateDeduction.cpp b/clang/lib/Sema/SemaTemplateDeduction.cpp
index 11bc9f2d1e7484..01f18e5a325197 100644
--- a/clang/lib/Sema/SemaTemplateDeduction.cpp
+++ b/clang/lib/Sema/SemaTemplateDeduction.cpp
@@ -3313,10 +3313,12 @@ FinishTemplateArgumentDeduction(
   if (Trap.hasErrorOccurred())
     return TemplateDeductionResult::SubstitutionFailure;
 
-  if (auto Result = CheckDeducedArgumentConstraints(S, Partial, SugaredBuilder,
-                                                    CanonicalBuilder, Info);
-      Result != TemplateDeductionResult::Success)
-    return Result;
+  if (!IsPartialOrdering) {
+    if (auto Result = CheckDeducedArgumentConstraints(
+            S, Partial, SugaredBuilder, CanonicalBuilder, Info);
+        Result != TemplateDeductionResult::Success)
+      return Result;
+  }
 
   return TemplateDeductionResult::Success;
 }
@@ -3364,13 +3366,16 @@ static TemplateDeductionResult FinishTemplateArgumentDeduction(
   if (Trap.hasErrorOccurred())
     return TemplateDeductionResult::SubstitutionFailure;
 
-  if (auto Result = CheckDeducedArgumentConstraints(S, Template, SugaredBuilder,
-                                                    CanonicalBuilder, Info);
-      Result != TemplateDeductionResult::Success)
-    return Result;
+  if (!PartialOrdering) {
+    if (auto Result = CheckDeducedArgumentConstraints(
+            S, Template, SugaredBuilder, CanonicalBuilder, Info);
+        Result != TemplateDeductionResult::Success)
+      return Result;
+  }
 
   return TemplateDeductionResult::Success;
 }
+
 /// Complete template argument deduction for DeduceTemplateArgumentsFromType.
 /// FIXME: this is mostly duplicated with the above two versions. Deduplicate
 /// the three implementations.
@@ -5595,19 +5600,8 @@ static TemplateDeductionResult FinishTemplateArgumentDeduction(
       TDR != TemplateDeductionResult::Success)
     return TDR;
 
-  // C++20 [temp.deduct]p5 - Only check constraints when all parameters have
-  // been deduced.
-  if (!IsIncomplete) {
-    if (auto Result = CheckDeducedArgumentConstraints(S, FTD, SugaredBuilder,
-                                                      CanonicalBuilder, Info);
-        Result != TemplateDeductionResult::Success)
-      return Result;
-  }
-
-  if (Trap.hasErrorOccurred())
-    return TemplateDeductionResult::SubstitutionFailure;
-
-  return TemplateDeductionResult::Success;
+  return Trap.hasErrorOccurred() ? TemplateDeductionResult::SubstitutionFailure
+                                 : TemplateDeductionResult::Success;
 }
 
 /// Determine whether the function template \p FT1 is at least as

[zyn0217]

LGTM, but please wait for others' opinions before merging.

[cor3ntin]

LGTM