[clang] [Clang][Sema] Report diagnostic for invalid mask in shufflevector (PR #221558)

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<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang

Author: Amr Hesham (AmrDeveloper)

<details>
<summary>Changes</summary>

Clang used to accept a vector with an integer representation as a valid mask; otherwise, it reported a type mismatch. This led to accepting a vector of booleans as a valid mask and reporting that types are not equal if both arguments are equal but not vectors of integers.

Currently, it checks for the mask type and reports a clear error message if the mask is a vector of bool or not a vector of integers

Fixes: #<!-- -->218132

---
Full diff: https://github.com/llvm/llvm-project/pull/221558.diff


4 Files Affected:

- (modified) clang/docs/ReleaseNotes.md (+2) 
- (modified) clang/include/clang/Basic/DiagnosticSemaKinds.td (+2) 
- (modified) clang/lib/Sema/SemaChecking.cpp (+11-2) 
- (added) clang/test/SemaCXX/vector-shuffle.cpp (+16) 


``````````diff
diff --git a/clang/docs/ReleaseNotes.md b/clang/docs/ReleaseNotes.md
index a43ed2b924622..0c4756572f52c 100644
--- a/clang/docs/ReleaseNotes.md
+++ b/clang/docs/ReleaseNotes.md
@@ -482,6 +482,8 @@ features cannot lower the translation-unit ABI level;
   dimension that is a zero integer constant, as in `struct Empty vla[n]` or
   `int vla[n][0]`. (#GH28328)
 
+- Clang now diagnoses passing wrong vector type as a mask to `__builtin_shufflevector`. (#GH218132)
+
 ### Improvements to Clang's time-trace
 
 ### Improvements to Coverage Mapping
diff --git a/clang/include/clang/Basic/DiagnosticSemaKinds.td b/clang/include/clang/Basic/DiagnosticSemaKinds.td
index 9bd0a526654c7..b118c9d0f3fbe 100644
--- a/clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -11446,6 +11446,8 @@ def err_shufflevector_argument_too_large : Error<
   "of vector elements">;
 def err_shufflevector_minus_one_is_undefined_behavior_constexpr : Error<
   "index for __builtin_shufflevector not within the bounds of the input vectors; index of -1 found at position %0 is not permitted in a constexpr context">;
+def err_shufflevector_incompatible_mask : Error<
+  "second argument to __builtin_shufflevector must be a vector of any integer type other than boolean (was %0)">;
 
 def err_convertvector_non_vector : Error<
   "first argument to __builtin_convertvector must be a vector">;
diff --git a/clang/lib/Sema/SemaChecking.cpp b/clang/lib/Sema/SemaChecking.cpp
index f0a1a529841b2..a670c8a19b1a5 100644
--- a/clang/lib/Sema/SemaChecking.cpp
+++ b/clang/lib/Sema/SemaChecking.cpp
@@ -6588,8 +6588,17 @@ ExprResult Sema::BuiltinShuffleVector(CallExpr *TheCall) {
     // with mask.  If so, verify that RHS is an integer vector type with the
     // same number of elts as lhs.
     if (NumArgs == 2) {
-      if (!RHSType->hasIntegerRepresentation() ||
-          RHSType->castAs<VectorType>()->getNumElements() != NumElements)
+      auto *RHSVecType = RHSType->castAs<VectorType>();
+      if (RHSVecType->getElementType()->isBooleanType() ||
+          !RHSVecType->getElementType()->isIntegerType()) {
+        return ExprError(Diag(TheCall->getBeginLoc(),
+                              diag::err_shufflevector_incompatible_mask)
+                         << RHSType
+                         << SourceRange(TheCall->getArg(0)->getBeginLoc(),
+                                        TheCall->getArg(1)->getEndLoc()));
+      }
+
+      if (RHSVecType->getNumElements() != NumElements)
         return ExprError(Diag(TheCall->getBeginLoc(),
                               diag::err_vec_builtin_incompatible_vector)
                          << TheCall->getDirectCallee()
diff --git a/clang/test/SemaCXX/vector-shuffle.cpp b/clang/test/SemaCXX/vector-shuffle.cpp
new file mode 100644
index 0000000000000..c204db2d02a39
--- /dev/null
+++ b/clang/test/SemaCXX/vector-shuffle.cpp
@@ -0,0 +1,16 @@
+// RUN: %clang_cc1 -triple x86_64-unknown-unknown %s -Wno-null-conversion -fsyntax-only -verify
+
+typedef bool v8b __attribute__((ext_vector_type(8)));
+typedef float v8f __attribute__((ext_vector_type(8)));
+
+void vector_of_bool_mask() {
+  v8b a;
+  v8b b;
+  auto r = __builtin_shufflevector(a, b); // expected-error {{second argument to __builtin_shufflevector must be a vector of any integer type other than boolean (was 'v8b' (vector of 8 'bool' values))}}
+}
+
+void vector_of_float_mask() {
+  v8f a;
+  v8f b;
+  auto r = __builtin_shufflevector(a, b); // expected-error {{second argument to __builtin_shufflevector must be a vector of any integer type other than boolean (was 'v8f' (vector of 8 'float' values))}}
+}

``````````

</details>


https://github.com/llvm/llvm-project/pull/221558