Daniel Dunbar | d057f7d | 2010-01-19 00:01:10 +0000 | [diff] [blame] | 1 | //===-- switch.S - Implement switch* --------------------------------------===// |
| 2 | // |
| 3 | // The LLVM Compiler Infrastructure |
| 4 | // |
Howard Hinnant | 9ad441f | 2010-11-16 22:13:33 +0000 | [diff] [blame] | 5 | // This file is dual licensed under the MIT and the University of Illinois Open |
| 6 | // Source Licenses. See LICENSE.TXT for details. |
Daniel Dunbar | d057f7d | 2010-01-19 00:01:10 +0000 | [diff] [blame] | 7 | // |
| 8 | //===----------------------------------------------------------------------===// |
| 9 | |
| 10 | #include "../assembly.h" |
| 11 | |
| 12 | // |
| 13 | // When compiling switch statements in thumb mode, the compiler |
| 14 | // can use these __switch* helper functions The compiler emits a blx to |
| 15 | // the __switch* function followed by a table of displacements for each |
| 16 | // case statement. On entry, R0 is the index into the table. The __switch* |
| 17 | // function uses the return address in lr to find the start of the table. |
| 18 | // The first entry in the table is the count of the entries in the table. |
| 19 | // It then uses R0 to index into the table and get the displacement of the |
| 20 | // address to jump to. If R0 is greater than the size of the table, it jumps |
| 21 | // to the last entry in the table. Each displacement in the table is actually |
| 22 | // the distance from lr to the label, thus making the tables PIC. |
| 23 | |
| 24 | |
| 25 | .text |
| 26 | .syntax unified |
| 27 | |
| 28 | // |
| 29 | // The table contains signed byte sized elements which are 1/2 the distance |
| 30 | // from lr to the target label. |
| 31 | // |
Nick Kledzik | d016b38 | 2010-04-21 22:36:23 +0000 | [diff] [blame] | 32 | .align 2 |
Daniel Dunbar | d057f7d | 2010-01-19 00:01:10 +0000 | [diff] [blame] | 33 | DEFINE_COMPILERRT_PRIVATE_FUNCTION(__switch8) |
| 34 | ldrb ip, [lr, #-1] // get first byte in table |
| 35 | cmp r0, ip // signed compare with index |
| 36 | ldrsbcc r0, [lr, r0] // get indexed byte out of table |
| 37 | ldrsbhs r0, [lr, ip] // if out of range, use last entry in table |
| 38 | add ip, lr, r0, lsl #1 // compute label = lr + element*2 |
| 39 | bx ip // jump to computed label |
| 40 | |
| 41 | // tell linker it can break up file at label boundaries |
| 42 | .subsections_via_symbols |
| 43 | |