[PATCH] D59403: [PowerPC] Add the support for __builtin_setrnd() in clang

[Zhang Kang via Phabricator via llvm-commits]

ZhangKang created this revision.
ZhangKang added reviewers: nemanjai, jsji, echristo, steven.zhang, hfinkel, hiraditya.

PowerPC64/PowerPC64le supports the builtin function __builtin_setrnd to set the floating point rounding mode. This function will use the least significant two bits of integer argument to set the floating point rounding mode.

double __builtin_setrnd(int mode);

The effective values for mode are:

  0 - round to nearest
  1 - round to zero
  2 - round to +infinity
  3 - round to -infinity

Note that the mode argument will modulo 4, so if the int argument is greater than 3, it will only use the least significant two bits of the mode. Namely, __builtin_setrnd(102)) is equal to __builtin_setrnd(2).


https://reviews.llvm.org/D59403

Files:
  clang/docs/LanguageExtensions.rst
  clang/include/clang/Basic/BuiltinsPPC.def
  clang/test/CodeGen/builtins-ppc.c


Index: clang/test/CodeGen/builtins-ppc.c
===================================================================
--- clang/test/CodeGen/builtins-ppc.c
+++ clang/test/CodeGen/builtins-ppc.c
@@ -14,3 +14,16 @@
   return __builtin_ppc_get_timebase();
 }
 
+void test_builtin_ppc_setrnd() {
+  volatile double res;
+  volatile int x = 100;
+  
+  // CHECK: call double @llvm.ppc.setrnd(i32 2)
+  res = __builtin_setrnd(2);
+
+  // CHECK: call double @llvm.ppc.setrnd(i32 100)
+  res = __builtin_setrnd(100);
+
+  // CHECK: call double @llvm.ppc.setrnd(i32 %2)
+  res = __builtin_setrnd(x);
+}
Index: clang/include/clang/Basic/BuiltinsPPC.def
===================================================================
--- clang/include/clang/Basic/BuiltinsPPC.def
+++ clang/include/clang/Basic/BuiltinsPPC.def
@@ -475,6 +475,9 @@
 BUILTIN(__builtin_unpack_vector_int128, "ULLiV1LLLii", "")
 BUILTIN(__builtin_pack_vector_int128, "V1LLLiULLiULLi", "")
 
+// Set the floating point rounding mode
+BUILTIN(__builtin_setrnd, "di", "")
+
 // FIXME: Obviously incomplete.
 
 #undef BUILTIN
Index: clang/docs/LanguageExtensions.rst
===================================================================
--- clang/docs/LanguageExtensions.rst
+++ clang/docs/LanguageExtensions.rst
@@ -2376,6 +2376,30 @@
           movl    %gs:(%eax), %eax
           ret
 
+PowerPC Language Extensions
+------------------------------
+
+Set the Floating Point Rounding Mode
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+PowerPC64/PowerPC64le supports the builtin function ``__builtin_setrnd`` to set
+the floating point rounding mode. This function will use the least significant
+two bits of integer argument to set the floating point rounding mode.
+
+.. code-block:: c++
+
+  double __builtin_setrnd(int mode);
+
+The effective values for mode are:
+
+    - 0 - round to nearest
+    - 1 - round to zero
+    - 2 - round to +infinity
+    - 3 - round to -infinity
+
+Note that the mode argument will modulo 4, so if the int argument is greater 
+than 3, it will only use the least significant two bits of the mode. 
+Namely, ``__builtin_setrnd(102))`` is equal to ``__builtin_setrnd(2)``.
+
 Extensions for Static Analysis
 ==============================
 


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