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 2-byte sized elements which are 1/2 the distance 30d057f7d5eec11c118af2a0620cb06495f03ca8b3Daniel Dunbar// from lr to the target label. 31d057f7d5eec11c118af2a0620cb06495f03ca8b3Daniel Dunbar// 322d1fdb26e458c4ddc04155c1d421bced3ba90cd0Stephen Hines .p2align 2 33d057f7d5eec11c118af2a0620cb06495f03ca8b3Daniel DunbarDEFINE_COMPILERRT_PRIVATE_FUNCTION(__switch16) 34d057f7d5eec11c118af2a0620cb06495f03ca8b3Daniel Dunbar ldrh ip, [lr, #-1] // get first 16-bit word in table 35d057f7d5eec11c118af2a0620cb06495f03ca8b3Daniel Dunbar cmp r0, ip // compare with index 36d057f7d5eec11c118af2a0620cb06495f03ca8b3Daniel Dunbar add r0, lr, r0, lsl #1 // compute address of element in table 37d057f7d5eec11c118af2a0620cb06495f03ca8b3Daniel Dunbar add ip, lr, ip, lsl #1 // compute address of last element in table 38abd768d337ffc997392323a70c8c53e459173d9bTim Northover ite lo 39abd768d337ffc997392323a70c8c53e459173d9bTim Northover ldrshlo r0, [r0, #1] // load 16-bit element if r0 is in range 40d057f7d5eec11c118af2a0620cb06495f03ca8b3Daniel Dunbar ldrshhs r0, [ip, #1] // load 16-bit element if r0 out of range 41d057f7d5eec11c118af2a0620cb06495f03ca8b3Daniel Dunbar add ip, lr, r0, lsl #1 // compute label = lr + element*2 42d057f7d5eec11c118af2a0620cb06495f03ca8b3Daniel Dunbar bx ip // jump to computed label 432d1fdb26e458c4ddc04155c1d421bced3ba90cd0Stephen HinesEND_COMPILERRT_FUNCTION(__switch16) 44d057f7d5eec11c118af2a0620cb06495f03ca8b3Daniel Dunbar 45c58a43648cd6121c51a2e795a28e2ef90d7813e6Pirama Arumuga NainarNO_EXEC_STACK_DIRECTIVE 46c58a43648cd6121c51a2e795a28e2ef90d7813e6Pirama Arumuga Nainar 47