[ESIMD] Allow non-const private statics in ESIMD kernels (#4264)

ESIMD already allows using private non-const globals in kernels.
This patch allows using private non-const statics for ESIMD.

This patch allows users to use static keyword to distinguish
global variables accross multiple translation units, e.g.:

// a.cpp
ESIMD_PRIVATE ESIMD_REGISTER(X) simd<T, N> GRF;
// b.cpp
ESIMD_PRIVATE ESIMD_REGISTER(Y) simd<T, N> GRF;

Linker will raise a validation of the ODR rule in this case.
To fix it we can declare those two variables as `static` without
changing their names.

Author: DenisBakhvalov

clang/lib/Sema/SemaExpr.cpp

@@ -225,12 +225,14 @@ bool Sema::DiagnoseUseOfDecl(NamedDecl *D, ArrayRef<SourceLocation> Locs,
           ExprEvalContexts.empty() ||
           (!isUnevaluatedContext() && !isConstantEvaluated());
       bool IsEsimdPrivateGlobal = isSYCLEsimdPrivateGlobal(VD);
-      if (IsRuntimeEvaluated && !IsConst &&
+      // Non-const statics are not allowed in SYCL except for ESIMD or with the
+      // SYCLGlobalVar attribute.
+      if (IsRuntimeEvaluated && !IsEsimdPrivateGlobal && !IsConst &&
           VD->getStorageClass() == SC_Static &&
           !VD->hasAttr<SYCLGlobalVarAttr>())
         SYCLDiagIfDeviceCode(*Locs.begin(), diag::err_sycl_restrict)
             << Sema::KernelNonConstStaticDataVariable;
-      // Non-const globals are allowed for SYCL explicit SIMD or with the
+      // Non-const globals are not allowed in SYCL except for ESIMD or with the
       // SYCLGlobalVar attribute.
       else if (IsRuntimeEvaluated && !IsEsimdPrivateGlobal && !IsConst &&
                VD->hasGlobalStorage() && !VD->hasAttr<SYCLGlobalVarAttr>())

clang/test/SemaSYCL/esimd-private-statics.cpp

@@ -0,0 +1,15 @@
+// RUN: %clang_cc1 -fsycl-is-device -fsyntax-only -verify -pedantic %s
+// expected-no-diagnostics
+
+// This test checks that non-const statics are allowed for ESIMD
+
+static __attribute__((opencl_private)) __attribute__((sycl_explicit_simd)) int esimdPrivStatic;
+
+struct S {
+  static __attribute__((opencl_private)) __attribute__((sycl_explicit_simd)) int esimdPrivStaticMember;
+};
+
+__attribute__((sycl_device)) __attribute__((sycl_explicit_simd)) void usage() {
+  esimdPrivStatic = 42;
+  S::esimdPrivStaticMember = 42;
+}