1 1.1 joerg //===-- switch.S - Implement switch* --------------------------------------===// 2 1.1 joerg // 3 1.1 joerg // The LLVM Compiler Infrastructure 4 1.1 joerg // 5 1.1 joerg // This file is dual licensed under the MIT and the University of Illinois Open 6 1.1 joerg // Source Licenses. See LICENSE.TXT for details. 7 1.1 joerg // 8 1.1 joerg //===----------------------------------------------------------------------===// 9 1.1 joerg 10 1.1 joerg #include "../assembly.h" 11 1.1 joerg 12 1.1 joerg // 13 1.1 joerg // When compiling switch statements in thumb mode, the compiler 14 1.1 joerg // can use these __switch* helper functions The compiler emits a blx to 15 1.1 joerg // the __switch* function followed by a table of displacements for each 16 1.1 joerg // case statement. On entry, R0 is the index into the table. The __switch* 17 1.1 joerg // function uses the return address in lr to find the start of the table. 18 1.1 joerg // The first entry in the table is the count of the entries in the table. 19 1.1 joerg // It then uses R0 to index into the table and get the displacement of the 20 1.1 joerg // address to jump to. If R0 is greater than the size of the table, it jumps 21 1.1 joerg // to the last entry in the table. Each displacement in the table is actually 22 1.1 joerg // the distance from lr to the label, thus making the tables PIC. 23 1.1 joerg 24 1.1 joerg 25 1.1 joerg .text 26 1.1 joerg .syntax unified 27 1.1 joerg 28 1.1 joerg // 29 1.1 joerg // The table contains signed byte sized elements which are 1/2 the distance 30 1.1 joerg // from lr to the target label. 31 1.1 joerg // 32 1.1.1.2 joerg .p2align 2 33 1.1 joerg DEFINE_COMPILERRT_PRIVATE_FUNCTION(__switch8) 34 1.1 joerg ldrb ip, [lr, #-1] // get first byte in table 35 1.1 joerg cmp r0, ip // signed compare with index 36 1.1 joerg ite lo 37 1.1 joerg ldrsblo r0, [lr, r0] // get indexed byte out of table 38 1.1 joerg ldrsbhs r0, [lr, ip] // if out of range, use last entry in table 39 1.1 joerg add ip, lr, r0, lsl #1 // compute label = lr + element*2 40 1.1 joerg bx ip // jump to computed label 41 1.1 joerg END_COMPILERRT_FUNCTION(__switch8) 42 1.1 joerg 43
Indexes created Wed Sep 24 05:09:52 GMT 2025