[FPEnv] Small fixes to implementation of flt.rounds

This change makes minor correction to the implementation of intrinsic
`llvm.flt.rounds`:
- Added documentation entry in LangRef,
- Attributes of the intrinsic changed to be in line with other functions
  dependent of floating-point environment.

Differential Revision: https://reviews.llvm.org/D79322

clang/include/clang/Basic/Builtins.def

@@ -323,6 +323,9 @@ BUILTIN(__builtin_truncf, "ff", "Fnc")
 BUILTIN(__builtin_truncl, "LdLd", "Fnc")
 BUILTIN(__builtin_truncf16, "hh", "Fnc")
 
+// Access to floating point environment
+BUILTIN(__builtin_flt_rounds, "i", "n")
+
 // C99 complex builtins
 BUILTIN(__builtin_cabs, "dXd", "Fne")
 BUILTIN(__builtin_cabsf, "fXf", "Fne")
@@ -517,7 +520,6 @@ BUILTIN(__builtin_return_address, "v*IUi", "n")
 BUILTIN(__builtin_extract_return_addr, "v*v*", "n")
 BUILTIN(__builtin_frame_address, "v*IUi", "n")
 BUILTIN(__builtin___clear_cache, "vc*c*", "n")
-BUILTIN(__builtin_flt_rounds, "i", "nc")
 BUILTIN(__builtin_setjmp, "iv**", "j")
 BUILTIN(__builtin_longjmp, "vv**i", "r")
 BUILTIN(__builtin_unwind_init, "v", "")

llvm/docs/LangRef.rst

@@ -18284,6 +18284,46 @@ This function returns the same values as the libm ``trunc`` functions
 would and handles error conditions in the same way.
 
 
+Floating Point Environment Manipulation intrinsics
+--------------------------------------------------
+
+These functions read or write floating point environment, such as rounding
+mode or state of floating point exceptions. Altering the floating point
+environment requires special care. See :ref:`Floating Point Environment <floatenv>`.
+
+'``llvm.flt.rounds``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+::
+
+      declare i32 @llvm.flt.rounds()
+
+Overview:
+"""""""""
+
+The '``llvm.flt.rounds``' intrinsic reads the current rounding mode.
+
+Semantics:
+""""""""""
+
+The '``llvm.flt.rounds``' intrinsic returns the current rounding mode.
+Encoding of the returned values is same as the result of ``FLT_ROUNDS``,
+specified by C standard:
+
+::
+
+    0  - toward zero
+    1  - to nearest, ties to even
+    2  - toward positive infinity
+    3  - toward negative infinity
+    4  - to nearest, ties away from zero
+
+Other values may be used to represent additional rounding modes, supported by a
+target. These values are target-specific.
+
 General Intrinsics
 ------------------
 

llvm/include/llvm/IR/Intrinsics.td

@@ -612,6 +612,13 @@ def int_objectsize : Intrinsic<[llvm_anyint_ty],
                                [IntrNoMem, IntrSpeculatable, IntrWillReturn, ImmArg<1>, ImmArg<2>, ImmArg<3>]>,
                                GCCBuiltin<"__builtin_object_size">;
 
+//===--------------- Access to Floating Point Environment -----------------===//
+//
+
+let IntrProperties = [IntrInaccessibleMemOnly, IntrWillReturn] in {
+  def int_flt_rounds    : Intrinsic<[llvm_i32_ty], []>;
+}
+
 //===--------------- Constrained Floating Point Intrinsics ----------------===//
 //
 
@@ -1115,8 +1122,6 @@ def int_coro_subfn_addr : Intrinsic<[llvm_ptr_ty], [llvm_ptr_ty, llvm_i8_ty],
 
 ///===-------------------------- Other Intrinsics --------------------------===//
 //
-def int_flt_rounds : Intrinsic<[llvm_i32_ty]>,
-                     GCCBuiltin<"__builtin_flt_rounds">;
 def int_trap : Intrinsic<[], [], [IntrNoReturn, IntrCold]>,
                GCCBuiltin<"__builtin_trap">;
 def int_debugtrap : Intrinsic<[]>,