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 signed 4-byte sized elements which are the distance
30// from lr to the target label.
31//
32	.p2align 2
33DEFINE_COMPILERRT_PRIVATE_FUNCTION(__switch32)
34	ldr     ip, [lr, #-1]            // get first 32-bit word in table
35	cmp     r0, ip                   // compare with index
36	add     r0, lr, r0, lsl #2       // compute address of element in table
37	add     ip, lr, ip, lsl #2       // compute address of last element in table
38	ite lo
39	ldrlo   r0, [r0, #3]             // load 32-bit element if r0 is in range
40	ldrhs   r0, [ip, #3]             // load 32-bit element if r0 out of range
41	add     ip, lr, r0               // compute label = lr + element
42	bx      ip                       // jump to computed label
43END_COMPILERRT_FUNCTION(__switch32)
44
45