projects / rustc.git / blame
| Commit | Line | Data |
|---|---|---|
| 1a4d82fc JJ |
1 | //===-- switch.S - Implement switch* --------------------------------------===// |
| 2 | // | |
| 3 | // The LLVM Compiler Infrastructure | |
| 4 | // | |
| 5 | // This file is dual licensed under the MIT and the University of Illinois Open | |
| 6 | // Source Licenses. See LICENSE.TXT for details. | |
| 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 unsigned byte sized elements which are 1/2 the distance | |
| 30 | // from lr to the target label. | |
| 31 | // | |
| 92a42be0 | 32 | .p2align 2 |
| 1a4d82fc JJ |
33 | DEFINE_COMPILERRT_PRIVATE_FUNCTION(__switchu8) |
| 34 | ldrb ip, [lr, #-1] // get first byte in table | |
| 35 | cmp r0, ip // compare with index | |
| 36 | ite lo | |
| 37 | ldrblo r0, [lr, r0] // get indexed byte out of table | |
| 38 | ldrbhs r0, [lr, ip] // if out of range, use last entry in table | |
| 39 | add ip, lr, r0, lsl #1 // compute label = lr + element*2 | |
| 40 | bx ip // jump to computed label | |
| 41 | END_COMPILERRT_FUNCTION(__switchu8) | |
| 42 |