Add __builtin_set_flt_rounds

This builtin will be converted to llvm.set.rounding intrinsic in IR level and should be work with "#pragma STDC FENV_ACCESS ON" since it changes default FP environment. Users can change rounding mode via this builtin without introducing libc dependency. Reviewed by: andrew.w.kaylor, rjmccall, sepavloff, aaron.ballman Differential Revision: https://reviews.llvm.org/D145765 Signed-off-by: jinge90 <ge.jin@intel.com>
llvm · Mar 15, 2023 · b38aa29 · b38aa29
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diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
@@ -304,6 +304,7 @@ Floating Point Support in Clang
 - Add ``__builtin_elementwise_log2`` builtin for floating point types only.
 - Add ``__builtin_elementwise_exp`` builtin for floating point types only.
 - Add ``__builtin_elementwise_exp2`` builtin for floating point types only.
+- Add ``__builtin_set_flt_rounds`` builtin for X86, x86_64, Arm and AArch64 only.
 
 AST Matchers
 ------------

diff --git a/clang/include/clang/Basic/Builtins.def b/clang/include/clang/Basic/Builtins.def
@@ -397,6 +397,7 @@ BUILTIN(__builtin_truncf16, "hh", "Fnc")
 
 // Access to floating point environment
 BUILTIN(__builtin_flt_rounds, "i", "n")
+BUILTIN(__builtin_set_flt_rounds, "vi", "n")
 
 // C99 complex builtins
 BUILTIN(__builtin_cabs, "dXd", "Fne")

diff --git a/clang/lib/CodeGen/CGBuiltin.cpp b/clang/lib/CodeGen/CGBuiltin.cpp
@@ -3381,6 +3381,14 @@ RValue CodeGenFunction::EmitBuiltinExpr(const GlobalDecl GD, unsigned BuiltinID,
     return RValue::get(Result);
   }
 
+  case Builtin::BI__builtin_set_flt_rounds: {
+    Function *F = CGM.getIntrinsic(Intrinsic::set_rounding);
+
+    Value *V = EmitScalarExpr(E->getArg(0));
+    Builder.CreateCall(F, V);
+    return RValue::get(nullptr);
+  }
+
   case Builtin::BI__builtin_fpclassify: {
     CodeGenFunction::CGFPOptionsRAII FPOptsRAII(*this, E);
     // FIXME: for strictfp/IEEE-754 we need to not trap on SNaN here.

diff --git a/clang/lib/Sema/SemaChecking.cpp b/clang/lib/Sema/SemaChecking.cpp
@@ -2146,6 +2146,14 @@ Sema::CheckBuiltinFunctionCall(FunctionDecl *FDecl, unsigned BuiltinID,
       return ExprError();
     break;
 
+  case Builtin::BI__builtin_set_flt_rounds:
+    if (CheckBuiltinTargetInSupported(*this, BuiltinID, TheCall,
+                                      {llvm::Triple::x86, llvm::Triple::x86_64,
+                                       llvm::Triple::arm, llvm::Triple::thumb,
+                                       llvm::Triple::aarch64}))
+      return ExprError();
+    break;
+
   case Builtin::BI__builtin_isgreater:
   case Builtin::BI__builtin_isgreaterequal:
   case Builtin::BI__builtin_isless:

diff --git a/clang/test/CodeGen/builtin_set_flt_rounds.c b/clang/test/CodeGen/builtin_set_flt_rounds.c
@@ -0,0 +1,8 @@
+// RUN: %clang_cc1 -triple x86_64-gnu-linux %s -emit-llvm -o - | FileCheck %s
+// RUN: %clang_cc1 -triple x86_64-windows-msvc %s -emit-llvm -o - | FileCheck %s
+// RUN: %clang_cc1 -triple aarch64-gnu-linux %s -emit-llvm -o - | FileCheck %s
+// RUN: %clang_cc1 -triple aarch64-windows-msvc %s -emit-llvm -o - | FileCheck %s
+void test_builtin_set_flt_rounds() {
+  __builtin_set_flt_rounds(1);
+  // CHECK: call void @llvm.set.rounding(i32 1)
+}
diff --git a/clang/test/Sema/builtin_set_flt_rounds.c b/clang/test/Sema/builtin_set_flt_rounds.c
@@ -0,0 +1,8 @@
+// RUN: %clang_cc1 -triple mipsel-unknown-linux -fsyntax-only %s -verify=expected,unsupported
+// RUN: %clang_cc1 -triple x86_64-gnu-linux -fsyntax-only %s -verify
+struct S {int a;};
+void test_builtin_set_flt_rounds() {
+  __builtin_set_flt_rounds(1); // unsupported-error {{builtin is not supported on this target}}
+  struct S s;
+  __builtin_set_flt_rounds(s); // expected-error {{passing 'struct S' to parameter of incompatible type}}
+}