[SveEmitter] Add builtins for svreinterpret

The reinterpret builtins are generated separately because they
need the cross product of all types, 121 functions in total,
which is inconvenient to specify in the arm_sve.td file.

Reviewers: SjoerdMeijer, efriedma, ctetreau, rengolin

Reviewed By: efriedma

Tags: #clang

Differential Revision: https://reviews.llvm.org/D78756

clang/lib/CodeGen/CGBuiltin.cpp

@@ -7917,6 +7917,19 @@ Value *CodeGenFunction::EmitAArch64SVEBuiltinExpr(unsigned BuiltinID,
   getContext().GetBuiltinType(BuiltinID, Error, &ICEArguments);
   assert(Error == ASTContext::GE_None && "Should not codegen an error");
 
+  llvm::Type *Ty = ConvertType(E->getType());
+  if (BuiltinID >= SVE::BI__builtin_sve_reinterpret_s8_s8 &&
+      BuiltinID <= SVE::BI__builtin_sve_reinterpret_f64_f64) {
+    Value *Val = EmitScalarExpr(E->getArg(0));
+    // FIXME: For big endian this needs an additional REV, or needs a separate
+    // intrinsic that is code-generated as a no-op, because the LLVM bitcast
+    // instruction is defined as 'bitwise' equivalent from memory point of
+    // view (when storing/reloading), whereas the svreinterpret builtin
+    // implements bitwise equivalent cast from register point of view.
+    // LLVM CodeGen for a bitcast must add an explicit REV for big-endian.
+    return Builder.CreateBitCast(Val, Ty);
+  }
+
   llvm::SmallVector<Value *, 4> Ops;
   for (unsigned i = 0, e = E->getNumArgs(); i != e; i++) {
     if ((ICEArguments & (1 << i)) == 0)
@@ -7939,7 +7952,6 @@ Value *CodeGenFunction::EmitAArch64SVEBuiltinExpr(unsigned BuiltinID,
   auto *Builtin = findARMVectorIntrinsicInMap(AArch64SVEIntrinsicMap, BuiltinID,
                                               AArch64SVEIntrinsicsProvenSorted);
   SVETypeFlags TypeFlags(Builtin->TypeModifier);
-  llvm::Type *Ty = ConvertType(E->getType());
   if (TypeFlags.isLoad())
     return EmitSVEMaskedLoad(E, Ty, Ops, Builtin->LLVMIntrinsic,
                              TypeFlags.isZExtReturn());