[clang] Report Diagnostic when builtin vector has negative size #166055

AmrDeveloper · 2025-11-02T11:28:49Z

Report a diagnostic in case vector_size or ext_vector_type attributes are used with a negative size. The same evaluation result can be used for other checks, for example, the too big a size.

Issue #165463

llvmbot · 2025-11-02T11:29:21Z

@llvm/pr-subscribers-clang

Author: Amr Hesham (AmrDeveloper)

Changes

Report a diagnostic in case vector_size or ext_vector_type attributes are used with a negative size. The same evaluation result can be used for other checks, for example, the too big a size.

Issue #165463

Full diff: https://github.com/llvm/llvm-project/pull/166055.diff

4 Files Affected:

(modified) clang/docs/ReleaseNotes.rst (+3)
(modified) clang/include/clang/Basic/DiagnosticSemaKinds.td (+2)
(modified) clang/lib/Sema/SemaType.cpp (+21-3)
(modified) clang/test/SemaCXX/vector.cpp (+5)

diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 92fc9381a5868..f3a8367ad16e5 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -390,6 +390,9 @@ Improvements to Clang's diagnostics
   that were previously incorrectly accepted in case of other irrelevant
   conditions are now consistently diagnosed, identical to C++ mode.
 
+- Clang now emits a diagnostic in case `vector_size` or `ext_vector_type`
+  attributes are used with a negative size (#GH165463).
+
 Improvements to Clang's time-trace
 ----------------------------------
 
diff --git a/clang/include/clang/Basic/DiagnosticSemaKinds.td b/clang/include/clang/Basic/DiagnosticSemaKinds.td
index 4e369be0bbb92..fa509536bf021 100644
--- a/clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -3510,6 +3510,8 @@ def err_init_method_bad_return_type : Error<
   "init methods must return an object pointer type, not %0">;
 def err_attribute_invalid_size : Error<
   "vector size not an integral multiple of component size">;
+def err_attribute_vec_negative_size
+    : Error<"vector must have non-negative size">;
 def err_attribute_zero_size : Error<"zero %0 size">;
 def err_attribute_size_too_large : Error<"%0 size too large">;
 def err_typecheck_sve_rvv_ambiguous : Error<
diff --git a/clang/lib/Sema/SemaType.cpp b/clang/lib/Sema/SemaType.cpp
index 280b3c92cce14..3345ed0dbbc0f 100644
--- a/clang/lib/Sema/SemaType.cpp
+++ b/clang/lib/Sema/SemaType.cpp
@@ -8285,10 +8285,20 @@ static void HandleVectorSizeAttr(QualType &CurType, const ParsedAttr &Attr,
 
   Expr *SizeExpr = Attr.getArgAsExpr(0);
   QualType T = S.BuildVectorType(CurType, SizeExpr, Attr.getLoc());
-  if (!T.isNull())
-    CurType = T;
-  else
+  if (T.isNull()) {
+    Attr.setInvalid();
+    return;
+  }
+
+  std::optional<llvm::APSInt> VecSize =
+      SizeExpr->getIntegerConstantExpr(S.Context);
+  if (VecSize && VecSize->isNegative()) {
+    S.Diag(SizeExpr->getExprLoc(), diag::err_attribute_vec_negative_size);
     Attr.setInvalid();
+    return;
+  }
+
+  CurType = T;
 }
 
 /// Process the OpenCL-like ext_vector_type attribute when it occurs on
@@ -8306,6 +8316,14 @@ static void HandleExtVectorTypeAttr(QualType &CurType, const ParsedAttr &Attr,
   QualType T = S.BuildExtVectorType(CurType, SizeExpr, Attr.getLoc());
   if (!T.isNull())
     CurType = T;
+
+  std::optional<llvm::APSInt> VecSize =
+      SizeExpr->getIntegerConstantExpr(S.Context);
+  if (VecSize && VecSize->isNegative()) {
+    S.Diag(SizeExpr->getExprLoc(), diag::err_attribute_vec_negative_size);
+    Attr.setInvalid();
+    return;
+  }
 }
 
 static bool isPermittedNeonBaseType(QualType &Ty, VectorKind VecKind, Sema &S) {
diff --git a/clang/test/SemaCXX/vector.cpp b/clang/test/SemaCXX/vector.cpp
index 808bdb679b09c..eea0b4756fae3 100644
--- a/clang/test/SemaCXX/vector.cpp
+++ b/clang/test/SemaCXX/vector.cpp
@@ -786,3 +786,8 @@ const long long e = *0; // expected-error {{indirection requires pointer operand
 double f = a - e;       // expected-error {{cannot initialize a variable of type 'double' with an rvalue of type '__attribute__((__vector_size__(1 * sizeof(double)))) double' (vector of 1 'double' value)}}
 int h = c - e;          // expected-error {{cannot initialize a variable of type 'int' with an rvalue of type '__attribute__((__vector_size__(1 * sizeof(long)))) long' (vector of 1 'long' value)}}
 }
+
+typedef int v_neg_size __attribute__((vector_size(-8))); // expected-error{{vector must have non-negative size}}
+typedef int v_neg_size_2 __attribute__((vector_size(-1 * 8))); // expected-error{{vector must have non-negative size}}
+typedef int v_ext_neg_size __attribute__((ext_vector_type(-8))); // expected-error{{vector must have non-negative size}}
+typedef int v_ext_neg_size2 __attribute__((ext_vector_type(-1 * 8))); // expected-error{{vector must have non-negative size}}

AaronBallman

Thank you for working on this!

AaronBallman · 2025-11-03T16:45:57Z

clang/lib/Sema/SemaType.cpp

+    return;
+  }
+
+  std::optional<llvm::APSInt> VecSize =


I think this logic should live in BuildVectorType() instead, near where we emit err_attribute_invalid_size.

AaronBallman · 2025-11-03T16:46:08Z

clang/lib/Sema/SemaType.cpp

+
+  std::optional<llvm::APSInt> VecSize =
+      SizeExpr->getIntegerConstantExpr(S.Context);
+  if (VecSize && VecSize->isNegative()) {


Similar, I think this should live in BuildExtVectorType().

AaronBallman · 2025-11-03T16:47:38Z

clang/test/SemaCXX/vector.cpp

+typedef int v_neg_size __attribute__((vector_size(-8))); // expected-error{{vector must have non-negative size}}
+typedef int v_neg_size_2 __attribute__((vector_size(-1 * 8))); // expected-error{{vector must have non-negative size}}
+typedef int v_ext_neg_size __attribute__((ext_vector_type(-8))); // expected-error{{vector must have non-negative size}}
+typedef int v_ext_neg_size2 __attribute__((ext_vector_type(-1 * 8))); // expected-error{{vector must have non-negative size}}


Another test case to add which I think won't be handled currently but will after moving into the Build functions is: https://godbolt.org/z/avobhW3Yx

Yes, it works. I just need to write this test in another file that allows C++11 extension to be able to use using

I forgot i can use ifdef to make it for specific version :D

I am not sure why the parameter name is ArraySize, not VectorSize or Size 🤔 ?

QualType Sema::BuildExtVectorType(QualType T, Expr *ArraySize, <---- SourceLocation AttrLoc)

I think that's just a think-o through refactoring, probably. Would be fine to rename in an NFC commit, IMO.

Thanks, I will create NFC for that soon @AaronBallman

Done #166208

AaronBallman

LGTM, thank you!

AaronBallman · 2025-11-03T18:17:07Z

clang/test/SemaCXX/vector.cpp

+typedef int v_neg_size __attribute__((vector_size(-8))); // expected-error{{vector must have non-negative size}}
+typedef int v_neg_size_2 __attribute__((vector_size(-1 * 8))); // expected-error{{vector must have non-negative size}}
+typedef int v_ext_neg_size __attribute__((ext_vector_type(-8))); // expected-error{{vector must have non-negative size}}
+typedef int v_ext_neg_size2 __attribute__((ext_vector_type(-1 * 8))); // expected-error{{vector must have non-negative size}}


I think that's just a think-o through refactoring, probably. Would be fine to rename in an NFC commit, IMO.

Fix the parameter name in the BuildExtVectorType function, also updating the code style to be consistent with BuildVectorType Discovered in #166055

[clang] Report Diagnostic when builtin vector has negative size

8173191

AmrDeveloper requested review from AaronBallman and shafik November 2, 2025 11:28

llvmbot added clang Clang issues not falling into any other category clang:frontend Language frontend issues, e.g. anything involving "Sema" labels Nov 2, 2025

AaronBallman reviewed Nov 3, 2025

View reviewed changes

Address code review comments

98f4923

AaronBallman approved these changes Nov 3, 2025

View reviewed changes

AmrDeveloper merged commit ecdd660 into llvm:main Nov 3, 2025
11 checks passed

This was referenced Nov 3, 2025

Clang Crash: Assertion Value > 0 failed in llvm::Align::Align due to negative vector_size attribute #165463

Closed

[clang][NFC] Fix BuildExtVectorType parameter name #166208

Merged

AmrDeveloper added a commit that referenced this pull request Nov 3, 2025

[clang][NFC] Fix BuildExtVectorType parameter name (#166208)

dd45c06

Fix the parameter name in the BuildExtVectorType function, also updating the code style to be consistent with BuildVectorType Discovered in #166055

[clang] Report Diagnostic when builtin vector has negative size #166055

[clang] Report Diagnostic when builtin vector has negative size #166055

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AmrDeveloper commented Nov 2, 2025

Uh oh!

llvmbot commented Nov 2, 2025

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AmrDeveloper Nov 3, 2025 •

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