Revert "[Clang] Preserve more sugars in constraint evaluation" #163322

zyn0217 · 2025-10-14T04:44:22Z

That patch breaks certain uses of VLAs when combined with constrained types.

This is a pre-existing issue that occurs when concepts are instantiated with sugar. See also #102353 and related PRs. I tried to fix it on top of the status quo in #163167, but that approach turned out to be unfeasible, and our maintainer was clearly unhappy with it, hence this revert.

Even after this patch, some VLA uses remain broken on trunk (see the example below), because our normalization patch depends on sugar to correctly compile libc++, due to a very subtle underlying bug. Still, this is the best attempt to mitigate the problem for now.

We discussed this and agreed that the long-term solution is to remove the sugar dependencies from concepts, before the VLA issue is properly resolved through a larger refactoring.

I'll add a related test (which passes with partially applied sugar) after this revert, since I don't have a reduced example yet.

This reverts commit d72cd24.

llvmbot · 2025-10-14T04:44:56Z

@llvm/pr-subscribers-clang

Author: Younan Zhang (zyn0217)

Changes

Reverts llvm/llvm-project#162991

That patch breaks certain uses of VLAs when combined with constrained types.

This is a pre-existing issue that occurs when concepts are instantiated with sugar. See also #102353 and related PRs. I tried to fix it on top of the status quo in #163167, but that approach turned out to be unfeasible, and our maintainer was clearly unhappy with it, hence this revert.

Even after this patch, some VLA uses remain broken on trunk (see the example below), because our normalization patch depends on sugar to correctly compile libc++, due to a very subtle underlying bug. Still, this is the best attempt to mitigate the problem for now.

We discussed this and agreed that the long-term solution is to remove the sugar dependencies from concepts, before the VLA issue is properly resolved through a larger refactoring.

I'll add a related test (which passes with partially applied sugar) after this revert, since I don't have a reduced example yet.

Full diff: https://github.com/llvm/llvm-project/pull/163322.diff

8 Files Affected:

(modified) clang/lib/Sema/SemaConcept.cpp (+2-1)
(modified) clang/test/CXX/expr/expr.prim/expr.prim.req/compound-requirement.cpp (+2-2)
(modified) clang/test/CXX/expr/expr.prim/expr.prim.req/nested-requirement.cpp (+1-1)
(modified) clang/test/CXX/temp/temp.param/p10-2a.cpp (+2-2)
(modified) clang/test/SemaHLSL/BuiltIns/Buffers.hlsl (+3-3)
(modified) clang/test/SemaHLSL/BuiltIns/RWBuffers.hlsl (+3-3)
(modified) clang/test/SemaTemplate/concepts-recursive-inst.cpp (+2-2)
(modified) clang/test/SemaTemplate/concepts.cpp (+4-4)

diff --git a/clang/lib/Sema/SemaConcept.cpp b/clang/lib/Sema/SemaConcept.cpp
index 7c44efd7b9c1c..9cbd1bd772f6f 100644
--- a/clang/lib/Sema/SemaConcept.cpp
+++ b/clang/lib/Sema/SemaConcept.cpp
@@ -614,7 +614,8 @@ ConstraintSatisfactionChecker::SubstitutionInTemplateArguments(
   for (unsigned I = 0, MappedIndex = 0; I < Used.size(); I++) {
     TemplateArgument Arg;
     if (Used[I])
-      Arg = CTAI.SugaredConverted[MappedIndex++];
+      Arg = S.Context.getCanonicalTemplateArgument(
+          CTAI.SugaredConverted[MappedIndex++]);
     if (I < SubstitutedOuterMost.size()) {
       SubstitutedOuterMost[I] = Arg;
       Offset = I + 1;
diff --git a/clang/test/CXX/expr/expr.prim/expr.prim.req/compound-requirement.cpp b/clang/test/CXX/expr/expr.prim/expr.prim.req/compound-requirement.cpp
index 5f1243a654f54..af2dce81d8a4b 100644
--- a/clang/test/CXX/expr/expr.prim/expr.prim.req/compound-requirement.cpp
+++ b/clang/test/CXX/expr/expr.prim/expr.prim.req/compound-requirement.cpp
@@ -149,7 +149,7 @@ namespace std_example {
   template<typename T> constexpr bool is_same_v<T, T> = true;
 
   template<typename T, typename U> concept same_as = is_same_v<T, U>;
-  // expected-note@-1 {{because 'is_same_v<int, typename T2::inner>' evaluated to false}}
+  // expected-note@-1 {{because 'is_same_v<int, typename std_example::T2::inner>' evaluated to false}}
 
   static_assert(C1<int>);
   static_assert(C1<int*>);
@@ -160,7 +160,7 @@ namespace std_example {
   template<typename T> concept C2 =
     requires(T x) {
       {*x} -> same_as<typename T::inner>;
-      // expected-note@-1{{because 'same_as<int, typename T2::inner>' evaluated to false}}
+      // expected-note@-1{{because 'same_as<int, typename std_example::T2::inner>' evaluated to false}}
       // expected-note@-2{{because '*x' would be invalid: indirection requires pointer operand ('int' invalid)}}
     };
 
diff --git a/clang/test/CXX/expr/expr.prim/expr.prim.req/nested-requirement.cpp b/clang/test/CXX/expr/expr.prim/expr.prim.req/nested-requirement.cpp
index 9fc4906459373..70a96bed05867 100644
--- a/clang/test/CXX/expr/expr.prim/expr.prim.req/nested-requirement.cpp
+++ b/clang/test/CXX/expr/expr.prim/expr.prim.req/nested-requirement.cpp
@@ -27,7 +27,7 @@ using r4i = X<void>::r4<int>; // expected-error{{constraints not satisfied for c
 
 // C++ [expr.prim.req.nested] Examples
 namespace std_example {
-  template<typename U> concept C1 = sizeof(U) == 1; // expected-note{{because 'sizeof(decltype(+t)) == 1' (4 == 1) evaluated to false}}
+  template<typename U> concept C1 = sizeof(U) == 1; // expected-note{{because 'sizeof(int) == 1' (4 == 1) evaluated to false}}
   template<typename T> concept D =
     requires (T t) {
       requires C1<decltype (+t)>; // expected-note{{because 'decltype(+t)' (aka 'int') does not satisfy 'C1'}}
diff --git a/clang/test/CXX/temp/temp.param/p10-2a.cpp b/clang/test/CXX/temp/temp.param/p10-2a.cpp
index 4f192d33ebe7e..c0406f88db5f3 100644
--- a/clang/test/CXX/temp/temp.param/p10-2a.cpp
+++ b/clang/test/CXX/temp/temp.param/p10-2a.cpp
@@ -95,8 +95,8 @@ concept OneOf = (is_same_v<T, Ts> || ...); // #OneOf
 // expected-note@#OneOf 3{{because 'is_same_v<int, char[1]>' evaluated to false}}
 // expected-note@#OneOf 3{{and 'is_same_v<int, char[2]>' evaluated to false}}
 // expected-note@#OneOf {{because 'is_same_v<decltype(nullptr), char>' evaluated to false}}
-// expected-note@#OneOf {{because 'is_same_v<decltype(nullptr), char>' evaluated to false}}
-// expected-note@#OneOf {{and 'is_same_v<decltype(nullptr), int>' evaluated to false}}
+// expected-note@#OneOf {{because 'is_same_v<std::nullptr_t, char>' evaluated to false}}
+// expected-note@#OneOf {{and 'is_same_v<std::nullptr_t, int>' evaluated to false}}
 // expected-note@#OneOf {{and 'is_same_v<decltype(nullptr), int>' evaluated to false}}
 
 template<OneOf<char[1], char[2]> T, OneOf<int, long, char> U>
diff --git a/clang/test/SemaHLSL/BuiltIns/Buffers.hlsl b/clang/test/SemaHLSL/BuiltIns/Buffers.hlsl
index 3f0a37d5d5a08..999372c95554e 100644
--- a/clang/test/SemaHLSL/BuiltIns/Buffers.hlsl
+++ b/clang/test/SemaHLSL/BuiltIns/Buffers.hlsl
@@ -20,7 +20,7 @@ Buffer<double2> r4;
 // expected-error@+4 {{constraints not satisfied for class template 'Buffer'}}
 // expected-note@*:* {{template declaration from hidden source: template <typename element_type> requires __is_typed_resource_element_compatible<element_type> class Buffer}}
 // expected-note@*:* {{because 'Buffer<int>' does not satisfy '__is_typed_resource_element_compatible'}}
-// expected-note@*:* {{because '__builtin_hlsl_is_typed_resource_element_compatible(Buffer<int>)' evaluated to false}}
+// expected-note@*:* {{because '__builtin_hlsl_is_typed_resource_element_compatible(hlsl::Buffer<int>)' evaluated to false}}
 Buffer<Buffer<int> > r5;
 
 struct s {
@@ -66,7 +66,7 @@ Buffer<half[4]> r10;
 typedef vector<int, 8> int8;
 // expected-error@+3 {{constraints not satisfied for class template 'Buffer'}}
 // expected-note@*:* {{because 'int8' (aka 'vector<int, 8>') does not satisfy '__is_typed_resource_element_compatible'}}
-// expected-note@*:* {{because '__builtin_hlsl_is_typed_resource_element_compatible(int8)' evaluated to false}}
+// expected-note@*:* {{because '__builtin_hlsl_is_typed_resource_element_compatible(vector<int, 8>)' evaluated to false}}
 Buffer<int8> r11;
 
 typedef int MyInt;
@@ -91,7 +91,7 @@ Buffer<numbers> r15;
 
 // expected-error@+3 {{constraints not satisfied for class template 'Buffer'}}
 // expected-note@*:* {{because 'double3' (aka 'vector<double, 3>') does not satisfy '__is_typed_resource_element_compatible'}}
-// expected-note@*:* {{because '__builtin_hlsl_is_typed_resource_element_compatible(double3)' evaluated to false}}
+// expected-note@*:* {{because '__builtin_hlsl_is_typed_resource_element_compatible(vector<double, 3>)' evaluated to false}}
 Buffer<double3> r16;
 
 
diff --git a/clang/test/SemaHLSL/BuiltIns/RWBuffers.hlsl b/clang/test/SemaHLSL/BuiltIns/RWBuffers.hlsl
index aa36c4838273e..b33f2af8a1117 100644
--- a/clang/test/SemaHLSL/BuiltIns/RWBuffers.hlsl
+++ b/clang/test/SemaHLSL/BuiltIns/RWBuffers.hlsl
@@ -20,7 +20,7 @@ RWBuffer<double2> r4;
 // expected-error@+4 {{constraints not satisfied for class template 'RWBuffer'}}
 // expected-note@*:* {{template declaration from hidden source: template <typename element_type> requires __is_typed_resource_element_compatible<element_type> class RWBuffer}}
 // expected-note@*:* {{because 'RWBuffer<int>' does not satisfy '__is_typed_resource_element_compatible'}}
-// expected-note@*:* {{because '__builtin_hlsl_is_typed_resource_element_compatible(RWBuffer<int>)' evaluated to false}}
+// expected-note@*:* {{because '__builtin_hlsl_is_typed_resource_element_compatible(hlsl::RWBuffer<int>)' evaluated to false}}
 RWBuffer<RWBuffer<int> > r5;
 
 struct s {
@@ -66,7 +66,7 @@ RWBuffer<half[4]> r10;
 typedef vector<int, 8> int8;
 // expected-error@+3 {{constraints not satisfied for class template 'RWBuffer'}}
 // expected-note@*:* {{because 'int8' (aka 'vector<int, 8>') does not satisfy '__is_typed_resource_element_compatible'}}
-// expected-note@*:* {{because '__builtin_hlsl_is_typed_resource_element_compatible(int8)' evaluated to false}}
+// expected-note@*:* {{because '__builtin_hlsl_is_typed_resource_element_compatible(vector<int, 8>)' evaluated to false}}
 RWBuffer<int8> r11;
 
 typedef int MyInt;
@@ -91,7 +91,7 @@ RWBuffer<numbers> r15;
 
 // expected-error@+3 {{constraints not satisfied for class template 'RWBuffer'}}
 // expected-note@*:* {{because 'double3' (aka 'vector<double, 3>') does not satisfy '__is_typed_resource_element_compatible'}}
-// expected-note@*:* {{because '__builtin_hlsl_is_typed_resource_element_compatible(double3)' evaluated to false}}
+// expected-note@*:* {{because '__builtin_hlsl_is_typed_resource_element_compatible(vector<double, 3>)' evaluated to false}}
 RWBuffer<double3> r16;
 
 
diff --git a/clang/test/SemaTemplate/concepts-recursive-inst.cpp b/clang/test/SemaTemplate/concepts-recursive-inst.cpp
index d36c6a8f02b20..73dce9317f383 100644
--- a/clang/test/SemaTemplate/concepts-recursive-inst.cpp
+++ b/clang/test/SemaTemplate/concepts-recursive-inst.cpp
@@ -68,8 +68,8 @@ struct my_range{
 void baz() {
 auto it = begin(rng); // #BEGIN_CALL
 // expected-error-re@#INF_REQ {{satisfaction of constraint {{.*}} depends on itself}}
-// expected-note@#INF_BEGIN {{while checking the satisfaction of concept 'Inf<struct my_range>' requested here}}
-// expected-note@#INF_BEGIN_EXPR {{while checking constraint satisfaction for template 'begin<struct my_range>' required here}}
+// expected-note@#INF_BEGIN {{while checking the satisfaction of concept 'Inf<DirectRecursiveCheck::my_range>' requested here}}
+// expected-note@#INF_BEGIN_EXPR {{while checking constraint satisfaction for template 'begin<DirectRecursiveCheck::my_range>' required here}}
 // expected-note@#INF_BEGIN_EXPR {{while substituting deduced template arguments into function template 'begin'}}
 // expected-note@#INF_BEGIN_EXPR {{in instantiation of requirement here}}
 // expected-note@#INF_REQ {{while substituting template arguments into constraint expression here}}
diff --git a/clang/test/SemaTemplate/concepts.cpp b/clang/test/SemaTemplate/concepts.cpp
index ee2bb8de66079..3fbe7c0ac650f 100644
--- a/clang/test/SemaTemplate/concepts.cpp
+++ b/clang/test/SemaTemplate/concepts.cpp
@@ -833,13 +833,13 @@ struct Parent {
 static_assert(Parent<void>::TakesUnary<int, 0>::i == 0);
 // expected-error@+3{{constraints not satisfied for class template 'TakesUnary'}}
 // expected-note@#UNARY{{because 'decltype(0ULL)' (aka 'unsigned long long') does not satisfy 'C'}}
-// expected-note@#61777_C{{because 'sizeof(decltype(0ULL)) == 4' (8 == 4) evaluated to false}}
+// expected-note@#61777_C{{because 'sizeof(unsigned long long) == 4' (8 == 4) evaluated to false}}
 static_assert(Parent<void>::TakesUnary<int, 0uLL>::i == 0);
 
 static_assert(Parent<int>::TakesBinary<int, 0>::i == 0);
 // expected-error@+3{{constraints not satisfied for class template 'TakesBinary'}}
 // expected-note@#BINARY{{because 'C2<decltype(0ULL), int>' evaluated to false}}
-// expected-note@#61777_C2{{because 'sizeof(decltype(0ULL)) == sizeof(int)' (8 == 4) evaluated to false}}
+// expected-note@#61777_C2{{because 'sizeof(unsigned long long) == sizeof(int)' (8 == 4) evaluated to false}}
 static_assert(Parent<int>::TakesBinary<int, 0ULL>::i == 0);
 }
 
@@ -1329,8 +1329,8 @@ static_assert(__cpp17_iterator<not_move_constructible>); \
 // expected-error {{static assertion failed}} \
 // expected-note {{because 'not_move_constructible' does not satisfy '__cpp17_iterator'}} \
 // expected-note@#__cpp17_copy_constructible {{because 'not_move_constructible' does not satisfy '__cpp17_copy_constructible'}} \
-// expected-note@#__cpp17_move_constructible {{because 'not_move_constructible' does not satisfy '__cpp17_move_constructible'}} \
-// expected-note@#is_move_constructible_v {{because 'is_move_constructible_v<not_move_constructible>' evaluated to false}}
+// expected-note@#__cpp17_move_constructible {{because 'parameter_mapping_regressions::case3::not_move_constructible' does not satisfy '__cpp17_move_constructible'}} \
+// expected-note@#is_move_constructible_v {{because 'is_move_constructible_v<parameter_mapping_regressions::case3::not_move_constructible>' evaluated to false}}
 }
 
 namespace case4 {

llvmbot · 2025-10-14T04:44:57Z

@llvm/pr-subscribers-hlsl

Author: Younan Zhang (zyn0217)

Changes

Reverts llvm/llvm-project#162991

That patch breaks certain uses of VLAs when combined with constrained types.

This is a pre-existing issue that occurs when concepts are instantiated with sugar. See also #102353 and related PRs. I tried to fix it on top of the status quo in #163167, but that approach turned out to be unfeasible, and our maintainer was clearly unhappy with it, hence this revert.

Even after this patch, some VLA uses remain broken on trunk (see the example below), because our normalization patch depends on sugar to correctly compile libc++, due to a very subtle underlying bug. Still, this is the best attempt to mitigate the problem for now.

We discussed this and agreed that the long-term solution is to remove the sugar dependencies from concepts, before the VLA issue is properly resolved through a larger refactoring.

I'll add a related test (which passes with partially applied sugar) after this revert, since I don't have a reduced example yet.

Full diff: https://github.com/llvm/llvm-project/pull/163322.diff

8 Files Affected:

(modified) clang/lib/Sema/SemaConcept.cpp (+2-1)
(modified) clang/test/CXX/expr/expr.prim/expr.prim.req/compound-requirement.cpp (+2-2)
(modified) clang/test/CXX/expr/expr.prim/expr.prim.req/nested-requirement.cpp (+1-1)
(modified) clang/test/CXX/temp/temp.param/p10-2a.cpp (+2-2)
(modified) clang/test/SemaHLSL/BuiltIns/Buffers.hlsl (+3-3)
(modified) clang/test/SemaHLSL/BuiltIns/RWBuffers.hlsl (+3-3)
(modified) clang/test/SemaTemplate/concepts-recursive-inst.cpp (+2-2)
(modified) clang/test/SemaTemplate/concepts.cpp (+4-4)

diff --git a/clang/lib/Sema/SemaConcept.cpp b/clang/lib/Sema/SemaConcept.cpp
index 7c44efd7b9c1c..9cbd1bd772f6f 100644
--- a/clang/lib/Sema/SemaConcept.cpp
+++ b/clang/lib/Sema/SemaConcept.cpp
@@ -614,7 +614,8 @@ ConstraintSatisfactionChecker::SubstitutionInTemplateArguments(
   for (unsigned I = 0, MappedIndex = 0; I < Used.size(); I++) {
     TemplateArgument Arg;
     if (Used[I])
-      Arg = CTAI.SugaredConverted[MappedIndex++];
+      Arg = S.Context.getCanonicalTemplateArgument(
+          CTAI.SugaredConverted[MappedIndex++]);
     if (I < SubstitutedOuterMost.size()) {
       SubstitutedOuterMost[I] = Arg;
       Offset = I + 1;
diff --git a/clang/test/CXX/expr/expr.prim/expr.prim.req/compound-requirement.cpp b/clang/test/CXX/expr/expr.prim/expr.prim.req/compound-requirement.cpp
index 5f1243a654f54..af2dce81d8a4b 100644
--- a/clang/test/CXX/expr/expr.prim/expr.prim.req/compound-requirement.cpp
+++ b/clang/test/CXX/expr/expr.prim/expr.prim.req/compound-requirement.cpp
@@ -149,7 +149,7 @@ namespace std_example {
   template<typename T> constexpr bool is_same_v<T, T> = true;
 
   template<typename T, typename U> concept same_as = is_same_v<T, U>;
-  // expected-note@-1 {{because 'is_same_v<int, typename T2::inner>' evaluated to false}}
+  // expected-note@-1 {{because 'is_same_v<int, typename std_example::T2::inner>' evaluated to false}}
 
   static_assert(C1<int>);
   static_assert(C1<int*>);
@@ -160,7 +160,7 @@ namespace std_example {
   template<typename T> concept C2 =
     requires(T x) {
       {*x} -> same_as<typename T::inner>;
-      // expected-note@-1{{because 'same_as<int, typename T2::inner>' evaluated to false}}
+      // expected-note@-1{{because 'same_as<int, typename std_example::T2::inner>' evaluated to false}}
       // expected-note@-2{{because '*x' would be invalid: indirection requires pointer operand ('int' invalid)}}
     };
 
diff --git a/clang/test/CXX/expr/expr.prim/expr.prim.req/nested-requirement.cpp b/clang/test/CXX/expr/expr.prim/expr.prim.req/nested-requirement.cpp
index 9fc4906459373..70a96bed05867 100644
--- a/clang/test/CXX/expr/expr.prim/expr.prim.req/nested-requirement.cpp
+++ b/clang/test/CXX/expr/expr.prim/expr.prim.req/nested-requirement.cpp
@@ -27,7 +27,7 @@ using r4i = X<void>::r4<int>; // expected-error{{constraints not satisfied for c
 
 // C++ [expr.prim.req.nested] Examples
 namespace std_example {
-  template<typename U> concept C1 = sizeof(U) == 1; // expected-note{{because 'sizeof(decltype(+t)) == 1' (4 == 1) evaluated to false}}
+  template<typename U> concept C1 = sizeof(U) == 1; // expected-note{{because 'sizeof(int) == 1' (4 == 1) evaluated to false}}
   template<typename T> concept D =
     requires (T t) {
       requires C1<decltype (+t)>; // expected-note{{because 'decltype(+t)' (aka 'int') does not satisfy 'C1'}}
diff --git a/clang/test/CXX/temp/temp.param/p10-2a.cpp b/clang/test/CXX/temp/temp.param/p10-2a.cpp
index 4f192d33ebe7e..c0406f88db5f3 100644
--- a/clang/test/CXX/temp/temp.param/p10-2a.cpp
+++ b/clang/test/CXX/temp/temp.param/p10-2a.cpp
@@ -95,8 +95,8 @@ concept OneOf = (is_same_v<T, Ts> || ...); // #OneOf
 // expected-note@#OneOf 3{{because 'is_same_v<int, char[1]>' evaluated to false}}
 // expected-note@#OneOf 3{{and 'is_same_v<int, char[2]>' evaluated to false}}
 // expected-note@#OneOf {{because 'is_same_v<decltype(nullptr), char>' evaluated to false}}
-// expected-note@#OneOf {{because 'is_same_v<decltype(nullptr), char>' evaluated to false}}
-// expected-note@#OneOf {{and 'is_same_v<decltype(nullptr), int>' evaluated to false}}
+// expected-note@#OneOf {{because 'is_same_v<std::nullptr_t, char>' evaluated to false}}
+// expected-note@#OneOf {{and 'is_same_v<std::nullptr_t, int>' evaluated to false}}
 // expected-note@#OneOf {{and 'is_same_v<decltype(nullptr), int>' evaluated to false}}
 
 template<OneOf<char[1], char[2]> T, OneOf<int, long, char> U>
diff --git a/clang/test/SemaHLSL/BuiltIns/Buffers.hlsl b/clang/test/SemaHLSL/BuiltIns/Buffers.hlsl
index 3f0a37d5d5a08..999372c95554e 100644
--- a/clang/test/SemaHLSL/BuiltIns/Buffers.hlsl
+++ b/clang/test/SemaHLSL/BuiltIns/Buffers.hlsl
@@ -20,7 +20,7 @@ Buffer<double2> r4;
 // expected-error@+4 {{constraints not satisfied for class template 'Buffer'}}
 // expected-note@*:* {{template declaration from hidden source: template <typename element_type> requires __is_typed_resource_element_compatible<element_type> class Buffer}}
 // expected-note@*:* {{because 'Buffer<int>' does not satisfy '__is_typed_resource_element_compatible'}}
-// expected-note@*:* {{because '__builtin_hlsl_is_typed_resource_element_compatible(Buffer<int>)' evaluated to false}}
+// expected-note@*:* {{because '__builtin_hlsl_is_typed_resource_element_compatible(hlsl::Buffer<int>)' evaluated to false}}
 Buffer<Buffer<int> > r5;
 
 struct s {
@@ -66,7 +66,7 @@ Buffer<half[4]> r10;
 typedef vector<int, 8> int8;
 // expected-error@+3 {{constraints not satisfied for class template 'Buffer'}}
 // expected-note@*:* {{because 'int8' (aka 'vector<int, 8>') does not satisfy '__is_typed_resource_element_compatible'}}
-// expected-note@*:* {{because '__builtin_hlsl_is_typed_resource_element_compatible(int8)' evaluated to false}}
+// expected-note@*:* {{because '__builtin_hlsl_is_typed_resource_element_compatible(vector<int, 8>)' evaluated to false}}
 Buffer<int8> r11;
 
 typedef int MyInt;
@@ -91,7 +91,7 @@ Buffer<numbers> r15;
 
 // expected-error@+3 {{constraints not satisfied for class template 'Buffer'}}
 // expected-note@*:* {{because 'double3' (aka 'vector<double, 3>') does not satisfy '__is_typed_resource_element_compatible'}}
-// expected-note@*:* {{because '__builtin_hlsl_is_typed_resource_element_compatible(double3)' evaluated to false}}
+// expected-note@*:* {{because '__builtin_hlsl_is_typed_resource_element_compatible(vector<double, 3>)' evaluated to false}}
 Buffer<double3> r16;
 
 
diff --git a/clang/test/SemaHLSL/BuiltIns/RWBuffers.hlsl b/clang/test/SemaHLSL/BuiltIns/RWBuffers.hlsl
index aa36c4838273e..b33f2af8a1117 100644
--- a/clang/test/SemaHLSL/BuiltIns/RWBuffers.hlsl
+++ b/clang/test/SemaHLSL/BuiltIns/RWBuffers.hlsl
@@ -20,7 +20,7 @@ RWBuffer<double2> r4;
 // expected-error@+4 {{constraints not satisfied for class template 'RWBuffer'}}
 // expected-note@*:* {{template declaration from hidden source: template <typename element_type> requires __is_typed_resource_element_compatible<element_type> class RWBuffer}}
 // expected-note@*:* {{because 'RWBuffer<int>' does not satisfy '__is_typed_resource_element_compatible'}}
-// expected-note@*:* {{because '__builtin_hlsl_is_typed_resource_element_compatible(RWBuffer<int>)' evaluated to false}}
+// expected-note@*:* {{because '__builtin_hlsl_is_typed_resource_element_compatible(hlsl::RWBuffer<int>)' evaluated to false}}
 RWBuffer<RWBuffer<int> > r5;
 
 struct s {
@@ -66,7 +66,7 @@ RWBuffer<half[4]> r10;
 typedef vector<int, 8> int8;
 // expected-error@+3 {{constraints not satisfied for class template 'RWBuffer'}}
 // expected-note@*:* {{because 'int8' (aka 'vector<int, 8>') does not satisfy '__is_typed_resource_element_compatible'}}
-// expected-note@*:* {{because '__builtin_hlsl_is_typed_resource_element_compatible(int8)' evaluated to false}}
+// expected-note@*:* {{because '__builtin_hlsl_is_typed_resource_element_compatible(vector<int, 8>)' evaluated to false}}
 RWBuffer<int8> r11;
 
 typedef int MyInt;
@@ -91,7 +91,7 @@ RWBuffer<numbers> r15;
 
 // expected-error@+3 {{constraints not satisfied for class template 'RWBuffer'}}
 // expected-note@*:* {{because 'double3' (aka 'vector<double, 3>') does not satisfy '__is_typed_resource_element_compatible'}}
-// expected-note@*:* {{because '__builtin_hlsl_is_typed_resource_element_compatible(double3)' evaluated to false}}
+// expected-note@*:* {{because '__builtin_hlsl_is_typed_resource_element_compatible(vector<double, 3>)' evaluated to false}}
 RWBuffer<double3> r16;
 
 
diff --git a/clang/test/SemaTemplate/concepts-recursive-inst.cpp b/clang/test/SemaTemplate/concepts-recursive-inst.cpp
index d36c6a8f02b20..73dce9317f383 100644
--- a/clang/test/SemaTemplate/concepts-recursive-inst.cpp
+++ b/clang/test/SemaTemplate/concepts-recursive-inst.cpp
@@ -68,8 +68,8 @@ struct my_range{
 void baz() {
 auto it = begin(rng); // #BEGIN_CALL
 // expected-error-re@#INF_REQ {{satisfaction of constraint {{.*}} depends on itself}}
-// expected-note@#INF_BEGIN {{while checking the satisfaction of concept 'Inf<struct my_range>' requested here}}
-// expected-note@#INF_BEGIN_EXPR {{while checking constraint satisfaction for template 'begin<struct my_range>' required here}}
+// expected-note@#INF_BEGIN {{while checking the satisfaction of concept 'Inf<DirectRecursiveCheck::my_range>' requested here}}
+// expected-note@#INF_BEGIN_EXPR {{while checking constraint satisfaction for template 'begin<DirectRecursiveCheck::my_range>' required here}}
 // expected-note@#INF_BEGIN_EXPR {{while substituting deduced template arguments into function template 'begin'}}
 // expected-note@#INF_BEGIN_EXPR {{in instantiation of requirement here}}
 // expected-note@#INF_REQ {{while substituting template arguments into constraint expression here}}
diff --git a/clang/test/SemaTemplate/concepts.cpp b/clang/test/SemaTemplate/concepts.cpp
index ee2bb8de66079..3fbe7c0ac650f 100644
--- a/clang/test/SemaTemplate/concepts.cpp
+++ b/clang/test/SemaTemplate/concepts.cpp
@@ -833,13 +833,13 @@ struct Parent {
 static_assert(Parent<void>::TakesUnary<int, 0>::i == 0);
 // expected-error@+3{{constraints not satisfied for class template 'TakesUnary'}}
 // expected-note@#UNARY{{because 'decltype(0ULL)' (aka 'unsigned long long') does not satisfy 'C'}}
-// expected-note@#61777_C{{because 'sizeof(decltype(0ULL)) == 4' (8 == 4) evaluated to false}}
+// expected-note@#61777_C{{because 'sizeof(unsigned long long) == 4' (8 == 4) evaluated to false}}
 static_assert(Parent<void>::TakesUnary<int, 0uLL>::i == 0);
 
 static_assert(Parent<int>::TakesBinary<int, 0>::i == 0);
 // expected-error@+3{{constraints not satisfied for class template 'TakesBinary'}}
 // expected-note@#BINARY{{because 'C2<decltype(0ULL), int>' evaluated to false}}
-// expected-note@#61777_C2{{because 'sizeof(decltype(0ULL)) == sizeof(int)' (8 == 4) evaluated to false}}
+// expected-note@#61777_C2{{because 'sizeof(unsigned long long) == sizeof(int)' (8 == 4) evaluated to false}}
 static_assert(Parent<int>::TakesBinary<int, 0ULL>::i == 0);
 }
 
@@ -1329,8 +1329,8 @@ static_assert(__cpp17_iterator<not_move_constructible>); \
 // expected-error {{static assertion failed}} \
 // expected-note {{because 'not_move_constructible' does not satisfy '__cpp17_iterator'}} \
 // expected-note@#__cpp17_copy_constructible {{because 'not_move_constructible' does not satisfy '__cpp17_copy_constructible'}} \
-// expected-note@#__cpp17_move_constructible {{because 'not_move_constructible' does not satisfy '__cpp17_move_constructible'}} \
-// expected-note@#is_move_constructible_v {{because 'is_move_constructible_v<not_move_constructible>' evaluated to false}}
+// expected-note@#__cpp17_move_constructible {{because 'parameter_mapping_regressions::case3::not_move_constructible' does not satisfy '__cpp17_move_constructible'}} \
+// expected-note@#is_move_constructible_v {{because 'is_move_constructible_v<parameter_mapping_regressions::case3::not_move_constructible>' evaluated to false}}
 }
 
 namespace case4 {

zyn0217 · 2025-10-14T04:49:48Z

The regression which fails before and after this revert (taken from #102353):

https://compiler-explorer.com/z/ozb6fM3zn

template <typename _Tp, typename>
concept same_as = true;

template <typename _Lhs>
concept assignable_from = requires {
  { 0 } -> same_as<_Lhs>;
};

template <typename _Iter>
struct span {
  _Iter iter;
};

template <assignable_from _Iter>
span(_Iter) -> span<_Iter>;

template <class T, T value>
void doHQScale() {
  int srcWidth = value; // expected-note 2{{declared here}}
  // We shouldn't crash with VLA types, which would appear when
  // substituting constraint expressions, as they are part of the sugars now.
  int edgeBuf_storage[srcWidth]; // expected-warning 2{{variable length arrays}} \
                                 // expected-note 2{{read of non-const variable 'srcWidth'}}
  span s(edgeBuf_storage);
}

void foo() {
  doHQScale<int, 42>(); // expected-note {{requested here}}
}

zyn0217 · 2025-10-14T06:24:23Z

Windows CI failure is unrelated

…163322) Reverts llvm#162991 That patch breaks certain uses of VLAs when combined with constrained types. This is a pre-existing issue that occurs when concepts are instantiated with sugar. See also llvm#102353 and related PRs. I tried to fix it on top of the status quo in llvm#163167, but that approach turned out to be unfeasible, and our maintainer was clearly unhappy with it, hence this revert. Even after this patch, some VLA uses remain broken on trunk (see the example below), because our normalization patch depends on sugar to correctly compile libc++, due to a very subtle underlying bug. Still, this is the best attempt to mitigate the problem for now. We discussed this and agreed that the long-term solution is to remove the sugar dependencies from concepts, before the VLA issue is properly resolved through a larger refactoring. I'll add a related test (which passes with partially applied sugar) after this revert, since I don't have a reduced example yet.

Revert "[Clang] Preserve more sugars in constraint evaluation (#162991)"

b5c37c8

This reverts commit d72cd24.

llvmbot added clang Clang issues not falling into any other category clang:frontend Language frontend issues, e.g. anything involving "Sema" HLSL HLSL Language Support labels Oct 14, 2025

zyn0217 enabled auto-merge (squash) October 14, 2025 04:50

zyn0217 mentioned this pull request Oct 14, 2025

[Clang] Preserve more sugars in constraint evaluation #162991

Merged

zyn0217 disabled auto-merge October 14, 2025 06:24

zyn0217 merged commit 5a560b3 into main Oct 14, 2025
16 of 18 checks passed

zyn0217 deleted the revert-162991-post-parameter-mapping branch October 14, 2025 06:24

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