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 4-byte sized elements which are 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(__switch32) 34 1.1 joerg ldr ip, [lr, #-1] // get first 32-bit word in table 35 1.1 joerg cmp r0, ip // compare with index 36 1.1 joerg add r0, lr, r0, lsl #2 // compute address of element in table 37 1.1 joerg add ip, lr, ip, lsl #2 // compute address of last element in table 38 1.1 joerg ite lo 39 1.1 joerg ldrlo r0, [r0, #3] // load 32-bit element if r0 is in range 40 1.1 joerg ldrhs r0, [ip, #3] // load 32-bit element if r0 out of range 41 1.1 joerg add ip, lr, r0 // compute label = lr + element 42 1.1 joerg bx ip // jump to computed label 43 1.1 joerg END_COMPILERRT_FUNCTION(__switch32) 44 1.1 joerg 45
Indexes created Tue Sep 23 07:09:52 GMT 2025