https://github.com/AaronBallman created
https://github.com/llvm/llvm-project/pull/141747
The assumption attribute is exposed with a Clang spelling, which means we
support __attribute__((assume)) as well as [[clang::assume]] as spellings for
the attribute.
In C++, the [[clang::assume]] spelling worked as expected. In C, that spelling
would emit an "unknown attribute ignored" diagnostic. This was happening
because we were failing to pass in the scope name and source location when
creating the attribute. In C++, this worked by chance because [[assume]] is a
known attribute in C++. But in C, where there is thankfully no [[assume]]
standard attribute, the lack of a scope meant we would set the attribute kind
to "unknown".
>From 83104f072456c346ecf9463e78804b19deaa64dd Mon Sep 17 00:00:00 2001
From: Aaron Ballman <aa...@aaronballman.com>
Date: Wed, 28 May 2025 07:55:20 -0400
Subject: [PATCH] [C] Fix parsing of [[clang::assume]]
The assumption attribute is exposed with a Clang spelling, which means
we support __attribute__((assume)) as well as [[clang::assume]] as
spellings for the attribute.
In C++, the [[clang::assume]] spelling worked as expected. In C, that
spelling would emit an "unknown attribute ignored" diagnostic. This was
happening because we were failing to pass in the scope name and source
location when creating the attribute. In C++, this worked by chance
because [[assume]] is a known attribute in C++. But in C, where there
is thankfully no [[assume]] standard attribute, the lack of a scope
meant we would set the attribute kind to "unknown".
---
clang/docs/ReleaseNotes.rst | 3 +++
clang/include/clang/Parse/Parser.h | 10 +++++-----
clang/lib/Parse/ParseDecl.cpp | 6 ++++--
clang/lib/Parse/ParseDeclCXX.cpp | 16 ++++++++--------
clang/test/Sema/assume.c | 25 +++++++++++++++++++++++++
5 files changed, 45 insertions(+), 15 deletions(-)
create mode 100644 clang/test/Sema/assume.c
diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 35ab1461e7b89..59086bd68d9b9 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -226,6 +226,9 @@ C Language Changes
- Added the existing ``-Wduplicate-decl-specifier`` diagnostic, which is on by
default, to ``-Wc++-compat`` because duplicated declaration specifiers are
not valid in C++.
+- The ``[[clang::assume()]]`` attribute is now correctly recognized in C. The
+ ``__attribute__((assume()))`` form has always been supported, so the fix is
+ specific to the attribute syntax used.
C2y Feature Support
^^^^^^^^^^^^^^^^^^^
diff --git a/clang/include/clang/Parse/Parser.h
b/clang/include/clang/Parse/Parser.h
index e6492b81dfff8..c4bef4729fd36 100644
--- a/clang/include/clang/Parse/Parser.h
+++ b/clang/include/clang/Parse/Parser.h
@@ -3037,11 +3037,11 @@ class Parser : public CodeCompletionHandler {
/// Parse the argument to C++23's [[assume()]] attribute. Returns true on
/// error.
- bool ParseCXXAssumeAttributeArg(ParsedAttributes &Attrs,
- IdentifierInfo *AttrName,
- SourceLocation AttrNameLoc,
- SourceLocation *EndLoc,
- ParsedAttr::Form Form);
+ bool
+ ParseCXXAssumeAttributeArg(ParsedAttributes &Attrs, IdentifierInfo *AttrName,
+ SourceLocation AttrNameLoc,
+ IdentifierInfo *ScopeName, SourceLocation
ScopeLoc,
+ SourceLocation *EndLoc, ParsedAttr::Form Form);
/// Try to parse an 'identifier' which appears within an attribute-token.
///
diff --git a/clang/lib/Parse/ParseDecl.cpp b/clang/lib/Parse/ParseDecl.cpp
index f7eb56426f6de..d6c36616bab47 100644
--- a/clang/lib/Parse/ParseDecl.cpp
+++ b/clang/lib/Parse/ParseDecl.cpp
@@ -676,7 +676,8 @@ void Parser::ParseGNUAttributeArgs(
Form);
return;
} else if (AttrKind == ParsedAttr::AT_CXXAssume) {
- ParseCXXAssumeAttributeArg(Attrs, AttrName, AttrNameLoc, EndLoc, Form);
+ ParseCXXAssumeAttributeArg(Attrs, AttrName, AttrNameLoc, ScopeName,
+ ScopeLoc, EndLoc, Form);
return;
}
@@ -734,7 +735,8 @@ unsigned Parser::ParseClangAttributeArgs(
break;
case ParsedAttr::AT_CXXAssume:
- ParseCXXAssumeAttributeArg(Attrs, AttrName, AttrNameLoc, EndLoc, Form);
+ ParseCXXAssumeAttributeArg(Attrs, AttrName, AttrNameLoc, ScopeName,
+ ScopeLoc, EndLoc, Form);
break;
}
return !Attrs.empty() ? Attrs.begin()->getNumArgs() : 0;
diff --git a/clang/lib/Parse/ParseDeclCXX.cpp b/clang/lib/Parse/ParseDeclCXX.cpp
index a665487a2f87d..2cf33a856c4f4 100644
--- a/clang/lib/Parse/ParseDeclCXX.cpp
+++ b/clang/lib/Parse/ParseDeclCXX.cpp
@@ -4452,11 +4452,10 @@ static bool
IsBuiltInOrStandardCXX11Attribute(IdentifierInfo *AttrName,
}
}
-bool Parser::ParseCXXAssumeAttributeArg(ParsedAttributes &Attrs,
- IdentifierInfo *AttrName,
- SourceLocation AttrNameLoc,
- SourceLocation *EndLoc,
- ParsedAttr::Form Form) {
+bool Parser::ParseCXXAssumeAttributeArg(
+ ParsedAttributes &Attrs, IdentifierInfo *AttrName,
+ SourceLocation AttrNameLoc, IdentifierInfo *ScopeName,
+ SourceLocation ScopeLoc, SourceLocation *EndLoc, ParsedAttr::Form Form) {
assert(Tok.is(tok::l_paren) && "Not a C++11 attribute argument list");
BalancedDelimiterTracker T(*this, tok::l_paren);
T.consumeOpen();
@@ -4498,8 +4497,8 @@ bool Parser::ParseCXXAssumeAttributeArg(ParsedAttributes
&Attrs,
ArgsUnion Assumption = Res.get();
auto RParen = Tok.getLocation();
T.consumeClose();
- Attrs.addNew(AttrName, SourceRange(AttrNameLoc, RParen), nullptr,
- SourceLocation(), &Assumption, 1, Form);
+ Attrs.addNew(AttrName, SourceRange(AttrNameLoc, RParen), ScopeName, ScopeLoc,
+ &Assumption, 1, Form);
if (EndLoc)
*EndLoc = RParen;
@@ -4565,7 +4564,8 @@ bool Parser::ParseCXX11AttributeArgs(
ScopeName, ScopeLoc, Form);
// So does C++23's assume() attribute.
else if (!ScopeName && AttrName->isStr("assume")) {
- if (ParseCXXAssumeAttributeArg(Attrs, AttrName, AttrNameLoc, EndLoc, Form))
+ if (ParseCXXAssumeAttributeArg(Attrs, AttrName, AttrNameLoc, nullptr,
+ SourceLocation{}, EndLoc, Form))
return true;
NumArgs = 1;
} else
diff --git a/clang/test/Sema/assume.c b/clang/test/Sema/assume.c
new file mode 100644
index 0000000000000..07a5490addfaf
--- /dev/null
+++ b/clang/test/Sema/assume.c
@@ -0,0 +1,25 @@
+// RUN: %clang_cc1 -std=c23 %s -verify
+
+// Validate that the attribute works in C.
+static_assert(!__has_c_attribute(assume));
+static_assert(__has_c_attribute(clang::assume));
+static_assert(__has_attribute(assume));
+
+void test(int n) {
+ // Smoke test.
+ __attribute__((assume(true)));
+ [[clang::assume(true)]];
+
+ // Test diagnostics
+ __attribute__((assume)); // expected-error {{'assume' attribute takes one
argument}}
+ __attribute__((assume())); // expected-error {{expected expression}}
+ [[clang::assume]]; // expected-error {{'assume' attribute takes one
argument}}
+ [[clang::assume()]]; // expected-error {{expected expression}}
+
+ __attribute__((assume(n++))); // expected-warning {{assumption is ignored
because it contains (potential) side-effects}}
+ [[clang::assume(n++)]]; // expected-warning {{assumption is ignored
because it contains (potential) side-effects}}
+
+ [[clang::assume(true)]] int x; // expected-error {{'assume' attribute
cannot be applied to a declaration}}
+ __attribute__((assume(true))) int y; // expected-error {{'assume' attribute
cannot be applied to a declaration}}
+}
+
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