make __builtin_isfinite more efficient (PR27145)

isinf (is infinite) and isfinite should be implemented with the same function
except we change the comparison operator.

See PR27145 for more details:
https://llvm.org/bugs/show_bug.cgi?id=27145

Ref: forked off of the discussion in D18513.

Differential Revision: http://reviews.llvm.org/D18648

llvm-svn: 265675

clang/lib/CodeGen/CGBuiltin.cpp

@@ -786,13 +786,19 @@ RValue CodeGenFunction::EmitBuiltinExpr(const FunctionDecl *FD,
     return RValue::get(Builder.CreateZExt(V, ConvertType(E->getType())));
   }
 
-  case Builtin::BI__builtin_isinf: {
-    // isinf(x) --> fabs(x) == infinity
+  case Builtin::BI__builtin_isinf:
+  case Builtin::BI__builtin_isfinite: {
+    // isinf(x)    --> fabs(x) == infinity
+    // isfinite(x) --> fabs(x) != infinity
+    // x != NaN via the ordered compare in either case.
     Value *V = EmitScalarExpr(E->getArg(0));
-    V = EmitFAbs(*this, V);
-
-    V = Builder.CreateFCmpOEQ(V, ConstantFP::getInfinity(V->getType()),"isinf");
-    return RValue::get(Builder.CreateZExt(V, ConvertType(E->getType())));
+    Value *Fabs = EmitFAbs(*this, V);
+    Constant *Infinity = ConstantFP::getInfinity(V->getType());
+    CmpInst::Predicate Pred = (BuiltinID == Builtin::BI__builtin_isinf)
+                                  ? CmpInst::FCMP_OEQ
+                                  : CmpInst::FCMP_ONE;
+    Value *FCmp = Builder.CreateFCmp(Pred, Fabs, Infinity, "cmpinf");
+    return RValue::get(Builder.CreateZExt(FCmp, ConvertType(E->getType())));
   }
 
   case Builtin::BI__builtin_isinf_sign: {
@@ -830,19 +836,6 @@ RValue CodeGenFunction::EmitBuiltinExpr(const FunctionDecl *FD,
     return RValue::get(Builder.CreateZExt(V, ConvertType(E->getType())));
   }
 
-  case Builtin::BI__builtin_isfinite: {
-    // isfinite(x) --> x == x && fabs(x) != infinity;
-    Value *V = EmitScalarExpr(E->getArg(0));
-    Value *Eq = Builder.CreateFCmpOEQ(V, V, "iseq");
-
-    Value *Abs = EmitFAbs(*this, V);
-    Value *IsNotInf =
-      Builder.CreateFCmpUNE(Abs, ConstantFP::getInfinity(V->getType()),"isinf");
-
-    V = Builder.CreateAnd(Eq, IsNotInf, "and");
-    return RValue::get(Builder.CreateZExt(V, ConvertType(E->getType())));
-  }
-
   case Builtin::BI__builtin_fpclassify: {
     Value *V = EmitScalarExpr(E->getArg(5));
     llvm::Type *Ty = ConvertType(E->getArg(5)->getType());

clang/test/CodeGen/builtins.c

@@ -217,10 +217,8 @@ void test_float_builtins(float F, double D, long double LD) {
   // CHECK:  select i1 %[[ISINF]], i32 %[[SIGN]], i32 0
 
   res = __builtin_isfinite(F);
-  // CHECK: fcmp oeq float 
   // CHECK: call float @llvm.fabs.f32(float
-  // CHECK: fcmp une float {{.*}}, 0x7FF0000000000000
-  // CHECK: and i1 
+  // CHECK: fcmp one float {{.*}}, 0x7FF0000000000000
 
   res = __builtin_isnormal(F);
   // CHECK: fcmp oeq float