RISC-V: Mark fsX as call clobbered when soft-float.

	2018-01-17  Andrew Waterman  <andrew@sifive.com>
	gcc/
	* config/riscv/riscv.c (riscv_conditional_register_usage): If
	UNITS_PER_FP_ARG is 0, set call_used_regs to 1 for all FP regs.

From-SVN: r256811

gcc/ChangeLog

+2018-01-17  Andrew Waterman  <andrew@sifive.com>
+
+	* config/riscv/riscv.c (riscv_conditional_register_usage): If
+	UNITS_PER_FP_ARG is 0, set call_used_regs to 1 for all FP regs.
+
 2018-01-17  David Malcolm  <dmalcolm@redhat.com>
 
 	PR lto/83121

gcc/config/riscv/riscv.c

@@ -4123,6 +4123,13 @@ riscv_conditional_register_usage (void)
       for (int regno = FP_REG_FIRST; regno <= FP_REG_LAST; regno++)
 	fixed_regs[regno] = call_used_regs[regno] = 1;
     }
+
+  /* In the soft-float ABI, there are no callee-saved FP registers.  */
+  if (UNITS_PER_FP_ARG == 0)
+    {
+      for (int regno = FP_REG_FIRST; regno <= FP_REG_LAST; regno++)
+	call_used_regs[regno] = 1;
+    }
 }
 
 /* Return a register priority for hard reg REGNO.  */