[Clang][Sema] Tweak tryCaptureVariable for unevaluated lambdas #93206

zyn0217 · 2024-05-23T15:31:17Z

This patch picks up #78598 with the hope that we can address such crashes in tryCaptureVariable for unevaluated lambdas.

In addition to tryCaptureVariable, this also contains several other fixes on e.g. lambda parsing/dependencies.

Fixes #63845
Fixes #67260
Fixes #69307
Fixes #88081
Fixes #89496
Fixes #90669
Fixes #91633

llvmbot · 2024-05-23T15:31:48Z

@llvm/pr-subscribers-clang

Author: Younan Zhang (zyn0217)

Changes

This patch picks up #78598 with the hope that we can address such crashes in tryCaptureVariable for unevaluated lambdas.

Fixes #88081
Fixes #69307
Fixes #91633
Fixes #90669
Fixes #89496

Full diff: https://github.com/llvm/llvm-project/pull/93206.diff

5 Files Affected:

(modified) clang/include/clang/AST/DeclBase.h (+4)
(modified) clang/lib/Sema/SemaExpr.cpp (+9)
(modified) clang/lib/Sema/SemaLambda.cpp (+10)
(modified) clang/lib/Sema/TreeTransform.h (+1-1)
(modified) clang/test/SemaCXX/lambda-unevaluated.cpp (+136)

diff --git a/clang/include/clang/AST/DeclBase.h b/clang/include/clang/AST/DeclBase.h
index e43e812cd9455..3a311d4c55916 100644
--- a/clang/include/clang/AST/DeclBase.h
+++ b/clang/include/clang/AST/DeclBase.h
@@ -2148,6 +2148,10 @@ class DeclContext {
            getDeclKind() <= Decl::lastRecord;
   }
 
+  bool isRequiresExprBody() const {
+    return getDeclKind() == Decl::RequiresExprBody;
+  }
+
   bool isNamespace() const { return getDeclKind() == Decl::Namespace; }
 
   bool isStdNamespace() const;
diff --git a/clang/lib/Sema/SemaExpr.cpp b/clang/lib/Sema/SemaExpr.cpp
index e6c3fa51d54da..bde4fcec69041 100644
--- a/clang/lib/Sema/SemaExpr.cpp
+++ b/clang/lib/Sema/SemaExpr.cpp
@@ -18831,6 +18831,9 @@ bool Sema::tryCaptureVariable(
   DeclContext *VarDC = Var->getDeclContext();
   DeclContext *DC = CurContext;
 
+  while (DC->isRequiresExprBody())
+    DC = DC->getParent();
+
   // tryCaptureVariable is called every time a DeclRef is formed,
   // it can therefore have non-negigible impact on performances.
   // For local variables and when there is no capturing scope,
@@ -18838,6 +18841,12 @@ bool Sema::tryCaptureVariable(
   if (CapturingFunctionScopes == 0 && (!BuildAndDiagnose || VarDC == DC))
     return true;
 
+  // Exception: We have not entered the function scope yet, but we're
+  // referencing the function parameters e.g. at the end of the function
+  // parameter list.
+  if (isa<ParmVarDecl>(Var) && !VarDC->isFunctionOrMethod())
+    return true;
+
   const auto *VD = dyn_cast<VarDecl>(Var);
   if (VD) {
     if (VD->isInitCapture())
diff --git a/clang/lib/Sema/SemaLambda.cpp b/clang/lib/Sema/SemaLambda.cpp
index 1743afaf15287..009c8b3bc57e5 100644
--- a/clang/lib/Sema/SemaLambda.cpp
+++ b/clang/lib/Sema/SemaLambda.cpp
@@ -1036,6 +1036,7 @@ void Sema::ActOnLambdaExpressionAfterIntroducer(LambdaIntroducer &Intro,
   // be dependent, because there are template parameters in scope.
   CXXRecordDecl::LambdaDependencyKind LambdaDependencyKind =
       CXXRecordDecl::LDK_Unknown;
+
   if (LSI->NumExplicitTemplateParams > 0) {
     Scope *TemplateParamScope = CurScope->getTemplateParamParent();
     assert(TemplateParamScope &&
@@ -1046,6 +1047,15 @@ void Sema::ActOnLambdaExpressionAfterIntroducer(LambdaIntroducer &Intro,
       LambdaDependencyKind = CXXRecordDecl::LDK_AlwaysDependent;
   } else if (CurScope->getTemplateParamParent() != nullptr) {
     LambdaDependencyKind = CXXRecordDecl::LDK_AlwaysDependent;
+  } else if (Scope *P = CurScope->getParent()) {
+    while (P->getEntity() && P->getEntity()->isRequiresExprBody())
+      P = P->getParent();
+    if (P->isFunctionDeclarationScope() &&
+        llvm::any_of(P->decls(), [](Decl *D) {
+          return isa<ParmVarDecl>(D) &&
+                 cast<ParmVarDecl>(D)->getType()->isTemplateTypeParmType();
+        }))
+      LambdaDependencyKind = CXXRecordDecl::LDK_AlwaysDependent;
   }
 
   CXXRecordDecl *Class = createLambdaClosureType(
diff --git a/clang/lib/Sema/TreeTransform.h b/clang/lib/Sema/TreeTransform.h
index c039b95293af2..bff4377e34110 100644
--- a/clang/lib/Sema/TreeTransform.h
+++ b/clang/lib/Sema/TreeTransform.h
@@ -14232,7 +14232,7 @@ TreeTransform<Derived>::TransformLambdaExpr(LambdaExpr *E) {
   // will be deemed as dependent even if there are no dependent template
   // arguments.
   // (A ClassTemplateSpecializationDecl is always a dependent context.)
-  while (DC->getDeclKind() == Decl::Kind::RequiresExprBody)
+  while (DC->isRequiresExprBody())
     DC = DC->getParent();
   if ((getSema().isUnevaluatedContext() ||
        getSema().isConstantEvaluatedContext()) &&
diff --git a/clang/test/SemaCXX/lambda-unevaluated.cpp b/clang/test/SemaCXX/lambda-unevaluated.cpp
index 10d4c2228ec9b..9892825067700 100644
--- a/clang/test/SemaCXX/lambda-unevaluated.cpp
+++ b/clang/test/SemaCXX/lambda-unevaluated.cpp
@@ -189,3 +189,139 @@ void recursive() {
 
 }
 }
+
+namespace GH88081 {
+
+struct S { //#S
+  S(auto value) //#S-ctor
+  requires requires { [&] -> decltype(value) { return 2; }; } {} // #S-requires
+
+  static auto foo(auto value) -> decltype([&]() -> decltype(value) {}()) { return {}; } // #S-foo
+
+  static auto bar(auto value) -> decltype([&] { return value; }()) {
+    return "a"; // #bar-body
+  }
+};
+
+S s("a"); // #use
+// expected-error@#S-requires {{cannot initialize return object of type 'decltype(value)' (aka 'const char *') with an rvalue of type 'int'}}
+// expected-error@#use {{no matching constructor}}
+// expected-note@#S-requires {{substituting into a lambda expression here}}
+// expected-note@#S-requires {{substituting template arguments into constraint expression here}}
+// expected-note@#S-requires {{in instantiation of requirement here}}
+// expected-note@#use {{checking constraint satisfaction for template 'S<const char *>' required here}}
+// expected-note@#use {{requested here}}
+// expected-note-re@#S 2{{candidate constructor {{.*}} not viable}}
+// expected-note@#S-ctor {{constraints not satisfied}}
+// expected-note-re@#S-requires {{because {{.*}} would be invalid}}
+
+void func() {
+  S::foo(42);
+  S::bar("str");
+  S::bar(0.618);
+  // expected-error-re@#bar-body {{cannot initialize return object of type {{.*}} (aka 'double') with an lvalue of type 'const char[2]'}}
+  // expected-note@-2 {{requested here}}
+}
+
+} // namespace GH88081
+
+namespace GH69307 {
+
+constexpr auto ICE() {
+  constexpr auto b = 1;
+  return [=](auto c) -> int
+           requires requires { b + c; }
+  { return 1; };
+};
+
+constexpr auto Ret = ICE()(1);
+
+constexpr auto ICE(auto a) { // template function, not lambda
+  return [=]()
+    requires requires { a; }
+  { return 1; };
+};
+
+} // namespace GH69307
+
+namespace GH91633 {
+
+struct __normal_iterator {};
+
+template <typename _Iterator>
+void operator==(_Iterator __lhs, _Iterator) // expected-note {{declared here}}
+  requires requires { __lhs; };
+
+__normal_iterator finder();
+
+template <typename >
+void findDetail() {
+  auto makeResult = [&](auto foo) -> void {
+    finder() != foo;
+    // expected-error@-1 {{function for rewritten '!=' comparison is not 'bool'}}
+  };
+  makeResult(__normal_iterator{}); // expected-note {{requested here}}
+}
+
+void find() {
+  findDetail<void>(); // expected-note {{requested here}}
+}
+} // namespace GH91633
+
+namespace GH90669 {
+
+struct __normal_iterator {};
+
+struct vector {
+  __normal_iterator begin(); // #begin
+  int end();
+};
+
+template <typename _IteratorR>
+bool operator==(_IteratorR __lhs, int)
+  requires requires { __lhs; }
+{}
+
+template <typename PrepareFunc> void queued_for_each(PrepareFunc prep) {
+  prep(vector{}); //#prep
+}
+
+void scan() {
+  queued_for_each([&](auto ino) -> int { // #queued-for-each
+    for (auto e : ino) { // #for-each
+      // expected-error@#for-each {{cannot increment value of type '__normal_iterator'}}
+      // expected-note-re@#prep {{instantiation {{.*}} requested here}}
+      // expected-note-re@#queued-for-each {{instantiation {{.*}} requested here}}
+      // expected-note@#for-each {{implicit call to 'operator++'}}
+      // expected-note@#begin {{selected 'begin' function}}
+    };
+  });
+}
+} // namespace GH90669
+
+namespace GH89496 {
+template <class Iter> struct RevIter {
+  Iter current;
+  constexpr explicit RevIter(Iter x) : current(x) {}
+  inline constexpr bool operator==(const RevIter<Iter> &other) const
+    requires requires {
+      // { current == other.current } -> std::convertible_to<bool>;
+      { other };
+    }
+  {
+    return true;
+  }
+};
+struct Foo {
+  Foo() {};
+};
+void CrashFunc() {
+  auto lambda = [&](auto from, auto to) -> Foo {
+    (void)(from == to);
+    return Foo();
+  };
+  auto from = RevIter<int *>(nullptr);
+  auto to = RevIter<int *>(nullptr);
+  lambda(from, to);
+}
+} // namespace pr89496

zyn0217 · 2024-05-23T15:33:35Z

Unfortunately, @l1nxy told me privately that he will not take over that patch as anticipated. So I hope I can continue the work.

I'll add a release note and supplement some comments tomorrow.

zyn0217 · 2024-05-23T15:37:25Z

clang/lib/Sema/SemaLambda.cpp

@@ -1036,6 +1036,7 @@ void Sema::ActOnLambdaExpressionAfterIntroducer(LambdaIntroducer &Intro,
  // be dependent, because there are template parameters in scope.
  CXXRecordDecl::LambdaDependencyKind LambdaDependencyKind =
      CXXRecordDecl::LDK_Unknown;
+


Adding a blank line so I can comment here: I found it interesting that we asserted in line 1033 that LSI->NumExplicitTemplateParams is always 0... so the lines in the first branch of the if below are useless?
@cor3ntin

This looks like dead code from a past refactor, we should remove it
(template parameters are set later, in ActOnLambdaExplicitTemplateParameterList

zyn0217 · 2024-05-23T15:41:36Z

~~(What's going on with the pre-commit CI? Does it disappear?)~~

EDIT: I pushed a commit again and it's back.

This patch picks up llvm#78598 with the hope that we can address such crashes in tryCaptureVariable for unevaluated lambdas. In addition to tryCaptureVariable, this also contains several other fixes on e.g. lambda parsing/dependencies.

erichkeane

I hope @cor3ntin comes and checks this out, but it generally looks OK to me. 1 oddity I'd like to hear about (why we can't do ActOnLambdaClosureQualifiers in the same place).

erichkeane · 2024-05-24T13:41:17Z

clang/lib/Parse/ParseExprCXX.cpp

@@ -1576,7 +1576,10 @@ ExprResult Parser::ParseLambdaExpressionAfterIntroducer(
                      TrailingReturnTypeLoc, &DS),
                  std::move(Attributes), DeclEndLoc);

-    Actions.ActOnLambdaClosureQualifiers(Intro, MutableLoc);
+    // We have called ActOnLambdaClosureQualifiers for parentheses-less cases


Is there any good reason to do this in 2 places, rather than just delay the above one to here? @cor3ntin ?

Yeah, looking into ActOnLambdaClosureQualifiers, I don't see anything that (currently) depends on lambda parameters. I guess we can combine these two calls? I'd love to open a separate NFC PR for doing so, before landing this patch. :)

@erichkeane I retrospected your comment in #78598 (comment) and I appreciate the diagnostics for non-ODR uses - however that's much like a QoI issue to me and would it be OK to leave it as a follow-up? Let me know what you think and I'll add a FIXME then.

I think I'd be ok with this as a followup. But @cor3ntin is the one who knows the most about lambda stuff (particularly parsing, etc), so I'd like to see him approve this.

Yes, we need to set whether the lambda has a mutable keyword as soon as the parameters, if present, are parsed, as that affect the meaning of subsequent id-expressions

When there are no parens, there can be a noexcept clause for example, and parsing that does requires knowing whether the lambda is mutable, so that we can adjust the type of any reference-to-capture.

Yes, we need to set whether the lambda has a mutable keyword as soon as the parameters, if present, are parsed, as that affect the meaning of subsequent id-expressions
When there are no parens, there can be a noexcept clause for example, and parsing that does requires knowing whether the lambda is mutable, so that we can adjust the type of any reference-to-capture.

Thanks, that makes sense! We currently set LSI->Mutable in ActOnLambdaClosureQualifiers() , and while I think it's possible to move it out of the function, I'm not opposed to leaving it as-is.

zyn0217 · 2024-06-03T09:56:45Z

@cor3ntin I have reduced the test cases (removed duplicate ones) and hopefully they look better. Can you please take another look? thanks!

cor3ntin

I think it makes sense.
I kinda wish there would be a more generic way to skip over requires expressions but I also can't think of other contexts we'd want to skip over, so this looks fine.

Thanks for fixing a large number of issues

See llvm/llvm-project#93206.

tobim · 2024-06-09T16:14:12Z

It would be great if this fix could be backported.

cor3ntin · 2024-06-09T16:42:40Z

It would be great if this fix could be backported.

I think it might be too late. cc @tstellar

zyn0217 · 2024-06-10T04:21:59Z

+1 for being too late because 18.1.7 just got rolled out a few days ago (I thought 18.1.6 was the final version of 18.x!), and there's probably no 18.1.8.

FireBurn · 2024-06-26T01:33:15Z

I've just bisected to the faulty commit and eventaully to this fix

+1 to get this added to 18.1.9 if there ever is one - especially if the Android NDK moves to it - the 27 betas fail for me too

zyn0217 · 2024-06-26T05:28:30Z

+1 to get this added to 18.1.9 if there ever is one - especially if the Android NDK moves to it - the 27 betas fail for me too

Sorry, I was unaware we had a scheduled release of 18.1.8 last week.

@tstellar @cor3ntin do you think this is worth another 18.x release (presumably 18.1.9), though we're near the end of the 19 development cycle? I can issue one if the situation is warranted.

See llvm/llvm-project#93206.

See llvm/llvm-project#93206. Co-authored-by: Alyssa Ross <[email protected]>

llvmbot added clang Clang issues not falling into any other category clang:frontend Language frontend issues, e.g. anything involving "Sema" labels May 23, 2024

zyn0217 commented May 23, 2024

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zyn0217 force-pushed the try-capture-variable branch from 5335704 to 658e9d4 Compare May 24, 2024 09:28

zyn0217 requested review from cor3ntin, erichkeane and Sirraide May 24, 2024 09:29

erichkeane reviewed May 24, 2024

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zyn0217 mentioned this pull request May 31, 2024

[Regression] clang 18 crashes at clang::Sema::tryCaptureVariable: Assertion idx < size() failed #93828

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zyn0217 linked an issue May 31, 2024 that may be closed by this pull request

[Regression] clang 18 crashes at clang::Sema::tryCaptureVariable: Assertion idx < size() failed #93828

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zyn0217 added 2 commits June 3, 2024 17:38

Cleanup duplicate tests

60aff76

Remove dead codes in ActOnLambdaExpressionAfterIntroducer

36d6277

cor3ntin reviewed Jun 3, 2024

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cor3ntin approved these changes Jun 3, 2024

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Merge branch 'main' into try-capture-variable

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zyn0217 merged commit 3d361b2 into llvm:main Jun 4, 2024
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zyn0217 deleted the try-capture-variable branch June 4, 2024 04:44

tobim added a commit to tobim/nixpkgs that referenced this pull request Jun 9, 2024

clang_18: Upstream patch to fix an ICE

c1aff8e

See llvm/llvm-project#93206.

tobim mentioned this pull request Jun 9, 2024

clang_18: Upstream patch to fix an ICE NixOS/nixpkgs#318565

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alyssais pushed a commit to tobim/nixpkgs that referenced this pull request Jul 5, 2024

clang_18: Upstream patch to fix an ICE

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See llvm/llvm-project#93206.

alyssais added a commit to tobim/nixpkgs that referenced this pull request Jul 5, 2024

clang_18: Upstream patch to fix an ICE

78c015e

See llvm/llvm-project#93206. Co-authored-by: Alyssa Ross <[email protected]>

alyssais added a commit to NixOS/nixpkgs that referenced this pull request Jul 5, 2024

clang_18: Upstream patch to fix an ICE

da06c32

See llvm/llvm-project#93206. Co-authored-by: Alyssa Ross <[email protected]>

FireBurn mentioned this pull request Aug 5, 2024

Error when building Linux with latest LLVM (and CLang) #72026

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MitalAshok mentioned this pull request Sep 8, 2024

clang++: error: clang frontend command failed with exit code 139 #107719

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[Clang][Sema] Tweak tryCaptureVariable for unevaluated lambdas #93206

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[Clang][Sema] Tweak tryCaptureVariable for unevaluated lambdas #93206

[Clang][Sema] Tweak tryCaptureVariable for unevaluated lambdas #93206

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