For multiply->add, loose underflow status, overflow when acc is

to-the-max, product can overflow result.

sim/testsuite/mips64r5900-elf/f-adda.s

@@ -0,0 +1,40 @@
+.include "t-macros.i"
+
+	start
+
+test_adda1:	
+	clearfcsr
+	loadfp $f1 4.0
+	loadfp $f2 0.1
+	adda.s $f1, $f2
+	checkacc 0 4.1
+
+test_add2:
+	clearfcsr
+	loadfp $f1 , -4.0
+	loadfp $f2 8.0
+	adda.s $f2, $f1
+	checkacc 0 4.0
+
+test_add3:
+	clearfcsr
+	loadfpmax $f1
+	loadfpmax $f2
+	adda.s $f2, $f1
+	checkaccmax FCSR_O
+
+test_add4:
+	clearfcsr
+	loadfpmax $f1
+	neg.s $f1, $f1
+	loadfpmax $f2
+	neg.s $f2, $f2
+	adda.s $f1, $f2
+	checkfcsr FCSR_O
+	clearfcsr
+	msub.s $f3, $f0, $f0
+	neg.s $f3, $f3
+	clearfcsr
+	checkfpmax 0 $f3
+
+	exit0