diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index ce98eb4f594..d0176663e3c 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,10 @@
+2010-03-19  Michael Matz  <matz@suse.de>
+
+	PR target/43305
+	* builtins.c (expand_builtin_interclass_mathfn,
+	expand_builtin_signbit): Use maybe_emit_unop_insn, emit libcalls
+	if that fails.
+
 2010-03-19  Richard Guenther  <rguenther@suse.de>
 
 	PR tree-optimization/43415
diff --git a/gcc/builtins.c b/gcc/builtins.c
index 705a25598b0..a68e743b616 100644
--- a/gcc/builtins.c
+++ b/gcc/builtins.c
@@ -2312,6 +2312,8 @@ expand_builtin_interclass_mathfn (tree exp, rtx target, rtx subtarget)
 
   if (icode != CODE_FOR_nothing)
     {
+      rtx last = get_last_insn ();
+      tree orig_arg = arg;
       /* Make a suitable register to place result in.  */
       if (!target
 	  || GET_MODE (target) != TYPE_MODE (TREE_TYPE (exp)))
@@ -2332,8 +2334,10 @@ expand_builtin_interclass_mathfn (tree exp, rtx target, rtx subtarget)
 
       /* Compute into TARGET.
 	 Set TARGET to wherever the result comes back.  */
-      emit_unop_insn (icode, target, op0, UNKNOWN);
-      return target;
+      if (maybe_emit_unop_insn (icode, target, op0, UNKNOWN))
+	return target;
+      delete_insns_since (last);
+      CALL_EXPR_ARG (exp, 0) = orig_arg;
     }
 
   return NULL_RTX;
@@ -5197,9 +5201,11 @@ expand_builtin_signbit (tree exp, rtx target)
   icode = signbit_optab->handlers [(int) fmode].insn_code;
   if (icode != CODE_FOR_nothing)
     {
+      rtx last = get_last_insn ();
       target = gen_reg_rtx (TYPE_MODE (TREE_TYPE (exp)));
-      emit_unop_insn (icode, target, temp, UNKNOWN);
-      return target;
+      if (maybe_emit_unop_insn (icode, target, temp, UNKNOWN))
+	return target;
+      delete_insns_since (last);
     }
 
   /* For floating point formats without a sign bit, implement signbit
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index 09f644d2e7f..39705477a34 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,8 @@
+2010-03-19  Michael Matz  <matz@suse.de>
+
+	PR target/43305
+	* gcc.dg/pr43305.c: New testcase.
+
 2010-03-19  Richard Guenther  <rguenther@suse.de>
 
 	PR tree-optimization/43415
diff --git a/gcc/testsuite/gcc.dg/pr43305.c b/gcc/testsuite/gcc.dg/pr43305.c
new file mode 100644
index 00000000000..c8aeaf23ccc
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr43305.c
@@ -0,0 +1,16 @@
+/* { dg-do compile } */
+/* { dg-options "-Os -ffast-math" } */
+extern int ilogbl(long double);
+extern int printf(const char *format, ...);
+
+__attribute__((noinline, noclone))
+int foo(long double x)
+{
+  return ilogbl(x);
+}
+
+int main()
+{
+  printf("%d\n", foo(100));
+  return 0;
+}