1d057f7d5eec11c118af2a0620cb06495f03ca8b3Daniel Dunbar//===-- switch.S - Implement switch* --------------------------------------===// 2d057f7d5eec11c118af2a0620cb06495f03ca8b3Daniel Dunbar// 3d057f7d5eec11c118af2a0620cb06495f03ca8b3Daniel Dunbar// The LLVM Compiler Infrastructure 4d057f7d5eec11c118af2a0620cb06495f03ca8b3Daniel Dunbar// 59ad441ffec97db647fee3725b3424284fb913e14Howard Hinnant// This file is dual licensed under the MIT and the University of Illinois Open 69ad441ffec97db647fee3725b3424284fb913e14Howard Hinnant// Source Licenses. See LICENSE.TXT for details. 7d057f7d5eec11c118af2a0620cb06495f03ca8b3Daniel Dunbar// 8d057f7d5eec11c118af2a0620cb06495f03ca8b3Daniel Dunbar//===----------------------------------------------------------------------===// 9d057f7d5eec11c118af2a0620cb06495f03ca8b3Daniel Dunbar 10d057f7d5eec11c118af2a0620cb06495f03ca8b3Daniel Dunbar#include "../assembly.h" 11d057f7d5eec11c118af2a0620cb06495f03ca8b3Daniel Dunbar 12d057f7d5eec11c118af2a0620cb06495f03ca8b3Daniel Dunbar// 13d057f7d5eec11c118af2a0620cb06495f03ca8b3Daniel Dunbar// When compiling switch statements in thumb mode, the compiler 14d057f7d5eec11c118af2a0620cb06495f03ca8b3Daniel Dunbar// can use these __switch* helper functions The compiler emits a blx to 15d057f7d5eec11c118af2a0620cb06495f03ca8b3Daniel Dunbar// the __switch* function followed by a table of displacements for each 16d057f7d5eec11c118af2a0620cb06495f03ca8b3Daniel Dunbar// case statement. On entry, R0 is the index into the table. The __switch* 17d057f7d5eec11c118af2a0620cb06495f03ca8b3Daniel Dunbar// function uses the return address in lr to find the start of the table. 18d057f7d5eec11c118af2a0620cb06495f03ca8b3Daniel Dunbar// The first entry in the table is the count of the entries in the table. 19d057f7d5eec11c118af2a0620cb06495f03ca8b3Daniel Dunbar// It then uses R0 to index into the table and get the displacement of the 20d057f7d5eec11c118af2a0620cb06495f03ca8b3Daniel Dunbar// address to jump to. If R0 is greater than the size of the table, it jumps 21d057f7d5eec11c118af2a0620cb06495f03ca8b3Daniel Dunbar// to the last entry in the table. Each displacement in the table is actually 22d057f7d5eec11c118af2a0620cb06495f03ca8b3Daniel Dunbar// the distance from lr to the label, thus making the tables PIC. 23d057f7d5eec11c118af2a0620cb06495f03ca8b3Daniel Dunbar 24d057f7d5eec11c118af2a0620cb06495f03ca8b3Daniel Dunbar 25d057f7d5eec11c118af2a0620cb06495f03ca8b3Daniel Dunbar .text 26d057f7d5eec11c118af2a0620cb06495f03ca8b3Daniel Dunbar .syntax unified 27d057f7d5eec11c118af2a0620cb06495f03ca8b3Daniel Dunbar 28d057f7d5eec11c118af2a0620cb06495f03ca8b3Daniel Dunbar// 29d057f7d5eec11c118af2a0620cb06495f03ca8b3Daniel Dunbar// The table contains signed byte sized elements which are 1/2 the distance 30d057f7d5eec11c118af2a0620cb06495f03ca8b3Daniel Dunbar// from lr to the target label. 31d057f7d5eec11c118af2a0620cb06495f03ca8b3Daniel Dunbar// 32d016b38b065fbe3e22584728c3b8bc55fc8a5f9cNick Kledzik .align 2 33d057f7d5eec11c118af2a0620cb06495f03ca8b3Daniel DunbarDEFINE_COMPILERRT_PRIVATE_FUNCTION(__switch8) 34d057f7d5eec11c118af2a0620cb06495f03ca8b3Daniel Dunbar ldrb ip, [lr, #-1] // get first byte in table 35d057f7d5eec11c118af2a0620cb06495f03ca8b3Daniel Dunbar cmp r0, ip // signed compare with index 36d057f7d5eec11c118af2a0620cb06495f03ca8b3Daniel Dunbar ldrsbcc r0, [lr, r0] // get indexed byte out of table 37d057f7d5eec11c118af2a0620cb06495f03ca8b3Daniel Dunbar ldrsbhs r0, [lr, ip] // if out of range, use last entry in table 38d057f7d5eec11c118af2a0620cb06495f03ca8b3Daniel Dunbar add ip, lr, r0, lsl #1 // compute label = lr + element*2 39d057f7d5eec11c118af2a0620cb06495f03ca8b3Daniel Dunbar bx ip // jump to computed label 40d057f7d5eec11c118af2a0620cb06495f03ca8b3Daniel Dunbar 41d057f7d5eec11c118af2a0620cb06495f03ca8b3Daniel Dunbar // tell linker it can break up file at label boundaries 42d057f7d5eec11c118af2a0620cb06495f03ca8b3Daniel Dunbar .subsections_via_symbols 43d057f7d5eec11c118af2a0620cb06495f03ca8b3Daniel Dunbar 44