1156cd587Sjoerg//===-- switch.S - Implement switch* --------------------------------------===// 2156cd587Sjoerg// 3156cd587Sjoerg// The LLVM Compiler Infrastructure 4156cd587Sjoerg// 5156cd587Sjoerg// This file is dual licensed under the MIT and the University of Illinois Open 6156cd587Sjoerg// Source Licenses. See LICENSE.TXT for details. 7156cd587Sjoerg// 8156cd587Sjoerg//===----------------------------------------------------------------------===// 9156cd587Sjoerg 10156cd587Sjoerg#include "../assembly.h" 11156cd587Sjoerg 12156cd587Sjoerg// 13156cd587Sjoerg// When compiling switch statements in thumb mode, the compiler 14156cd587Sjoerg// can use these __switch* helper functions The compiler emits a blx to 15156cd587Sjoerg// the __switch* function followed by a table of displacements for each 16156cd587Sjoerg// case statement. On entry, R0 is the index into the table. The __switch* 17156cd587Sjoerg// function uses the return address in lr to find the start of the table. 18156cd587Sjoerg// The first entry in the table is the count of the entries in the table. 19156cd587Sjoerg// It then uses R0 to index into the table and get the displacement of the 20156cd587Sjoerg// address to jump to. If R0 is greater than the size of the table, it jumps 21156cd587Sjoerg// to the last entry in the table. Each displacement in the table is actually 22156cd587Sjoerg// the distance from lr to the label, thus making the tables PIC. 23156cd587Sjoerg 24156cd587Sjoerg 25156cd587Sjoerg .text 26156cd587Sjoerg .syntax unified 27156cd587Sjoerg 28156cd587Sjoerg// 29156cd587Sjoerg// The table contains signed byte sized elements which are 1/2 the distance 30156cd587Sjoerg// from lr to the target label. 31156cd587Sjoerg// 32*61f2f256Sjoerg .p2align 2 33156cd587SjoergDEFINE_COMPILERRT_PRIVATE_FUNCTION(__switch8) 34156cd587Sjoerg ldrb ip, [lr, #-1] // get first byte in table 35156cd587Sjoerg cmp r0, ip // signed compare with index 36156cd587Sjoerg ite lo 37156cd587Sjoerg ldrsblo r0, [lr, r0] // get indexed byte out of table 38156cd587Sjoerg ldrsbhs r0, [lr, ip] // if out of range, use last entry in table 39156cd587Sjoerg add ip, lr, r0, lsl #1 // compute label = lr + element*2 40156cd587Sjoerg bx ip // jump to computed label 41156cd587SjoergEND_COMPILERRT_FUNCTION(__switch8) 42156cd587Sjoerg 43