[clang][SVE] Don't warn on vector to sizeless builtin implicit conversion

This commit prevents warnings from -Wconversion when a clang vector type
is implicitly converted to a sizeless builtin type -- for example, when
implicitly converting a fixed-predicate to a scalable predicate.

The code below:

     1    #include <arm_sve.h>
     2
     3    #define N __ARM_FEATURE_SVE_BITS
     4    #define FIXED_ATTR __attribute__((arm_sve_vector_bits (N)))
     5    typedef svbool_t fixed_svbool_t FIXED_ATTR;
     6
     7    inline fixed_svbool_t foo(fixed_svbool_t p) {
     8      return svnot_z(svptrue_b64(), p);
     9    }

would previously raise this warning:

    warning: implicit conversion turns vector to scalar: \
    'fixed_svbool_t' (vector of 8 'unsigned char' values) to 'svbool_t' \
    (aka '__SVBool_t') [-Wconversion]

Note that many cases of these implicit conversions were already
permitted because many functions inside arm_sve.h are spawned via
preprocessor macros, and the call to isInSystemMacro would cover us in
this case. This commit fixes the remaining cases.

Differential Revision: https://reviews.llvm.org/D97053

1 files changed, 10 insertions, 1 deletions

diff --git a/clang/lib/Sema/SemaChecking.cpp b/clang/lib/Sema/SemaChecking.cpp
index 2d3d36f..b41d943 100644
--- a/clang/lib/Sema/SemaChecking.cpp
+++ b/clang/lib/Sema/SemaChecking.cpp
@@ -12051,7 +12051,16 @@ static void CheckImplicitConversion(Sema &S, Expr *E, QualType T,
     checkObjCDictionaryLiteral(S, QualType(Target, 0), DictionaryLiteral);
 
   // Strip vector types.
-  if (isa<VectorType>(Source)) {
+  if (const auto *SourceVT = dyn_cast<VectorType>(Source)) {
+    if (Target->isVLSTBuiltinType()) {
+      auto SourceVectorKind = SourceVT->getVectorKind();
+      if (SourceVectorKind == VectorType::SveFixedLengthDataVector ||
+          SourceVectorKind == VectorType::SveFixedLengthPredicateVector ||
+          (SourceVectorKind == VectorType::GenericVector &&
+           S.Context.getTypeSize(Source) == S.getLangOpts().ArmSveVectorBits))
+        return;
+    }
+
     if (!isa<VectorType>(Target)) {
       if (S.SourceMgr.isInSystemMacro(CC))
         return;