[PATCH] CodeGen: Emit sqrt intrinsic from __builtin_sqrt

[Tom Stellard]

Hi doug.gregor, hfinkel,

We need to add a check for x < -0.0 before the intrinsic, because it has undefined behavior in this case.

REPOSITORY
  rL LLVM

http://reviews.llvm.org/D8468

Files:
  lib/CodeGen/CGBuiltin.cpp
  test/CodeGen/builtins.c

Index: lib/CodeGen/CGBuiltin.cpp
===================================================================
--- lib/CodeGen/CGBuiltin.cpp
+++ lib/CodeGen/CGBuiltin.cpp
@@ -1364,6 +1364,22 @@
     return RValue::get(Builder.CreateCall(F, Arg0));
   }
 
+  case Builtin::BI__builtin_sqrt:
+  case Builtin::BI__builtin_sqrtf:
+  case Builtin::BI__builtin_sqrtl: {
+    // Lib functions with the __builtin prefix don't set errno, so we can safely
+    // use the intrinsic here.  We just need to add a check for x < -0.0
+    Value *Arg0 = EmitScalarExpr(E->getArg(0));
+    llvm::Type *ArgType = Arg0->getType();
+    Value *F = CGM.getIntrinsic(Intrinsic::sqrt, ArgType);
+    Value *Sqrt = Builder.CreateCall(F, Arg0);
+    Value *Cmp = Builder.CreateFCmpOLT(Arg0,
+                                       ConstantFP::getNegativeZero(ArgType));
+    return RValue::get(Builder.CreateSelect(Cmp, ConstantFP::getNaN(ArgType),
+                                                 Sqrt));
+
+  }
+
   case Builtin::BI__builtin_pow:
   case Builtin::BI__builtin_powf:
   case Builtin::BI__builtin_powl:
Index: test/CodeGen/builtins.c
===================================================================
--- test/CodeGen/builtins.c
+++ test/CodeGen/builtins.c
@@ -236,3 +236,25 @@
   // CHECK: call i64 @llvm.readcyclecounter()
   return __builtin_readcyclecounter();
 }
+
+// CHECK-LABEL: define void @test_float_builtin_libcalls
+void test_float_builtin_libcalls(float F, double D, long double LD) {
+  volatile float resf;
+  volatile double resd;
+  volatile long double resld;
+
+  resf = __builtin_sqrtf(F);
+  // CHECK-DAG: [[SQRTF:%.*]] = call float @llvm.sqrt.f32(float
+  // CHECK-DAG: [[FCMPF:%.*]] = fcmp olt float {{.*}}, -0.000000e+00
+  // CHECK: select i1 [[FCMPF]], float 0x7FF8000000000000, float [[SQRTF]]
+
+  resd = __builtin_sqrt(D);
+  // CHECK-DAG: [[SQRTD:%.*]] = call double @llvm.sqrt.f64(double
+  // CHECK-DAG: [[FCMPD:%.*]] = fcmp olt double {{.*}}, -0.000000e+00
+  // CHECK: select i1 [[FCMPD]], double 0x7FF8000000000000, double [[SQRTD]]
+
+  resld = __builtin_sqrtl(LD);
+  // CHECK-DAG: [[SQRTL:%.*]] = call x86_fp80 @llvm.sqrt.f80(x86_fp80
+  // CHECK-DAG: [[FCMPL:%.*]] = fcmp olt x86_fp80 {{.*}}, 0xK80000000000000000000
+  // CHECK: select i1 [[FCMPL]], x86_fp80 0xK7FFFC000000000000000, x86_fp80 [[SQRTL]]
+}

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