Merge pull request #243 from kito-cheng/struct-pass-in-reg-rule

Clarify how struct pass in register

Author: kito-cheng

riscv-cc.adoc

@@ -109,8 +109,8 @@ Aggregates whose total size is no more than XLEN bits are passed in
 a register, with the fields laid out as though they were passed in memory. If
 no register is available, the aggregate is passed on the stack.
 Aggregates whose total size is no more than 2×XLEN bits are passed in a pair
-of registers; if only one register is available, the first half is passed in
-a register and the second half is passed on the stack. If no registers are
+of registers; if only one register is available, the first XLEN bits are passed
+in a register and the remaining bits are passed on the stack. If no registers are
 available, the aggregate is passed on the stack. Bits unused due to
 padding, and bits past the end of an aggregate whose size in bits is not
 divisible by XLEN, are undefined.