1*0a6a1f1dSLionel Sambuc//===-- switch.S - Implement switch* --------------------------------------===// 2*0a6a1f1dSLionel Sambuc// 3*0a6a1f1dSLionel Sambuc// The LLVM Compiler Infrastructure 4*0a6a1f1dSLionel Sambuc// 5*0a6a1f1dSLionel Sambuc// This file is dual licensed under the MIT and the University of Illinois Open 6*0a6a1f1dSLionel Sambuc// Source Licenses. See LICENSE.TXT for details. 7*0a6a1f1dSLionel Sambuc// 8*0a6a1f1dSLionel Sambuc//===----------------------------------------------------------------------===// 9*0a6a1f1dSLionel Sambuc 10*0a6a1f1dSLionel Sambuc#include "../assembly.h" 11*0a6a1f1dSLionel Sambuc 12*0a6a1f1dSLionel Sambuc// 13*0a6a1f1dSLionel Sambuc// When compiling switch statements in thumb mode, the compiler 14*0a6a1f1dSLionel Sambuc// can use these __switch* helper functions The compiler emits a blx to 15*0a6a1f1dSLionel Sambuc// the __switch* function followed by a table of displacements for each 16*0a6a1f1dSLionel Sambuc// case statement. On entry, R0 is the index into the table. The __switch* 17*0a6a1f1dSLionel Sambuc// function uses the return address in lr to find the start of the table. 18*0a6a1f1dSLionel Sambuc// The first entry in the table is the count of the entries in the table. 19*0a6a1f1dSLionel Sambuc// It then uses R0 to index into the table and get the displacement of the 20*0a6a1f1dSLionel Sambuc// address to jump to. If R0 is greater than the size of the table, it jumps 21*0a6a1f1dSLionel Sambuc// to the last entry in the table. Each displacement in the table is actually 22*0a6a1f1dSLionel Sambuc// the distance from lr to the label, thus making the tables PIC. 23*0a6a1f1dSLionel Sambuc 24*0a6a1f1dSLionel Sambuc 25*0a6a1f1dSLionel Sambuc .text 26*0a6a1f1dSLionel Sambuc .syntax unified 27*0a6a1f1dSLionel Sambuc 28*0a6a1f1dSLionel Sambuc// 29*0a6a1f1dSLionel Sambuc// The table contains signed byte sized elements which are 1/2 the distance 30*0a6a1f1dSLionel Sambuc// from lr to the target label. 31*0a6a1f1dSLionel Sambuc// 32*0a6a1f1dSLionel Sambuc .p2align 2 33*0a6a1f1dSLionel SambucDEFINE_COMPILERRT_PRIVATE_FUNCTION(__switch8) 34*0a6a1f1dSLionel Sambuc ldrb ip, [lr, #-1] // get first byte in table 35*0a6a1f1dSLionel Sambuc cmp r0, ip // signed compare with index 36*0a6a1f1dSLionel Sambuc ite lo 37*0a6a1f1dSLionel Sambuc ldrsblo r0, [lr, r0] // get indexed byte out of table 38*0a6a1f1dSLionel Sambuc ldrsbhs r0, [lr, ip] // if out of range, use last entry in table 39*0a6a1f1dSLionel Sambuc add ip, lr, r0, lsl #1 // compute label = lr + element*2 40*0a6a1f1dSLionel Sambuc bx ip // jump to computed label 41*0a6a1f1dSLionel SambucEND_COMPILERRT_FUNCTION(__switch8) 42*0a6a1f1dSLionel Sambuc 43