libclc: remove __attribute__((assume)) for clspv targets

Instead add a proper attribute in clang, and add convert it to
function metadata to keep the information in the IR.
The goal is to remove the dependency on __attribute__((assume)) that
should have not be there in the first place.

Ref llvm#84934

Author: rjodinchr

clang/docs/ReleaseNotes.rst

@@ -393,6 +393,10 @@ Attribute Changes in Clang
 - Clang now warns that the ``exclude_from_explicit_instantiation`` attribute
   is ignored when applied to a local class or a member thereof.
 
+- The ``clspv_libclc_builtin`` attribute has been added to allow clspv
+  (`OpenCL-C to Vulkan SPIR-V compiler <https://github.com/google/clspv>`_) to identify functions coming from libclc
+  (`OpenCL-C builtin library <https://libclc.llvm.org>`_).
+
 Improvements to Clang's diagnostics
 -----------------------------------
 - Clang now applies syntax highlighting to the code snippets it

clang/include/clang/Basic/Attr.td

@@ -4561,3 +4561,10 @@ def CodeAlign: StmtAttr {
     static constexpr int MaximumAlignment = 4096;
   }];
 }
+
+def ClspvLibclcBuiltin: InheritableAttr {
+  let Spellings = [Clang<"clspv_libclc_builtin">];
+  let Subjects = SubjectList<[Function]>;
+  let Documentation = [ClspvLibclcBuiltinDoc];
+  let SimpleHandler = 1;
+}

clang/include/clang/Basic/AttrDocs.td

@@ -8087,3 +8087,17 @@ requirement:
   }
   }];
 }
+
+def ClspvLibclcBuiltinDoc : Documentation {
+  let Category = DocCatFunction;
+  let Content = [{
+Attribute used by `clspv`_ (OpenCL-C to Vulkan SPIR-V compiler) to identify functions coming from `libclc`_ (OpenCL-C builtin library).
+
+.. code-block:: c
+
+  void __attribute__((clspv_libclc_builtin)) libclc_builtin() {}
+
+.. _`clspv`: https://github.com/google/clspv
+.. _`libclc`: https://libclc.llvm.org
+}];
+}

clang/lib/CodeGen/CodeGenFunction.cpp

@@ -979,6 +979,11 @@ void CodeGenFunction::StartFunction(GlobalDecl GD, QualType RetTy,
     EmitKernelMetadata(FD, Fn);
   }
 
+  if (FD && FD->hasAttr<ClspvLibclcBuiltinAttr>()) {
+    Fn->setMetadata("clspv_libclc_builtin",
+                    llvm::MDNode::get(getLLVMContext(), {}));
+  }
+
   // If we are checking function types, emit a function type signature as
   // prologue data.
   if (FD && SanOpts.has(SanitizerKind::Function)) {

clang/test/CodeGen/clspv_libclc_builtin.c

@@ -0,0 +1,6 @@
+// RUN: %clang_cc1 -triple spir -emit-llvm %s -o - | FileCheck %s
+
+// CHECK: @foo()
+// CHECK-SAME: !clspv_libclc_builtin
+
+void __attribute__((clspv_libclc_builtin)) foo() {}

libclc/generic/include/clc/clcfunc.h

@@ -7,8 +7,7 @@
 #if defined(CLC_SPIRV) || defined(CLC_SPIRV64)
 #define _CLC_DEF
 #elif defined(CLC_CLSPV) || defined(CLC_CLSPV64)
-#define _CLC_DEF                                                               \
-  __attribute__((noinline)) __attribute__((assume("clspv_libclc_builtin")))
+#define _CLC_DEF __attribute__((noinline)) __attribute__((clspv_libclc_builtin))
 #else
 #define _CLC_DEF __attribute__((always_inline))
 #endif