16059Samurai//===-- switch.S - Implement switch* --------------------------------------===// 26059Samurai// 36059Samurai// The LLVM Compiler Infrastructure 46059Samurai// 56059Samurai// This file is dual licensed under the MIT and the University of Illinois Open 66059Samurai// Source Licenses. See LICENSE.TXT for details. 76059Samurai// 86059Samurai//===----------------------------------------------------------------------===// 96059Samurai 106059Samurai#include "../assembly.h" 116059Samurai 126059Samurai// 136059Samurai// When compiling switch statements in thumb mode, the compiler 146059Samurai// can use these __switch* helper functions The compiler emits a blx to 156059Samurai// the __switch* function followed by a table of displacements for each 166059Samurai// case statement. On entry, R0 is the index into the table. The __switch* 176059Samurai// function uses the return address in lr to find the start of the table. 186059Samurai// The first entry in the table is the count of the entries in the table. 198857Srgrimes// It then uses R0 to index into the table and get the displacement of the 2010858Samurai// address to jump to. If R0 is greater than the size of the table, it jumps 218857Srgrimes// to the last entry in the table. Each displacement in the table is actually 226059Samurai// the distance from lr to the label, thus making the tables PIC. 236059Samurai 246059Samurai 256059Samurai .text 266059Samurai .syntax unified 276059Samurai 286059Samurai// 296059Samurai// The table contains unsigned byte sized elements which are 1/2 the distance 306059Samurai// from lr to the target label. 316059Samurai// 326059Samurai .align 2 336059SamuraiDEFINE_COMPILERRT_PRIVATE_FUNCTION(__switchu8) 346059Samurai ldrb ip, [lr, #-1] // get first byte in table 356059Samurai cmp r0, ip // compare with index 366059Samurai ldrbcc r0, [lr, r0] // get indexed byte out of table 376735Samurai ldrbhs r0, [lr, ip] // if out of range, use last entry in table 386059Samurai add ip, lr, r0, lsl #1 // compute label = lr + element*2 396059Samurai bx ip // jump to computed label 406059Samurai 416059Samurai // tell linker it can break up file at label boundaries 426059Samurai .subsections_via_symbols 436059Samurai 446059Samurai