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//===-- switch.S - Implement switch* --------------------------------------===//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
#include "../assembly.h"
// When compiling switch statements in thumb mode, the compiler
// can use these __switch* helper functions The compiler emits a blx to
// the __switch* function followed by a table of displacements for each
// case statement. On entry, R0 is the index into the table. The __switch*
// function uses the return address in lr to find the start of the table.
// The first entry in the table is the count of the entries in the table.
// It then uses R0 to index into the table and get the displacement of the
// address to jump to. If R0 is greater than the size of the table, it jumps
// to the last entry in the table. Each displacement in the table is actually
// the distance from lr to the label, thus making the tables PIC.
.syntax unified
// The table contains unsigned byte sized elements which are 1/2 the distance
// from lr to the target label.
.p2align 2
ldrb ip, [lr, #-1] // get first byte in table
cmp r0, ip // compare with index
ite lo
ldrblo r0, [lr, r0] // get indexed byte out of table
ldrbhs r0, [lr, ip] // if out of range, use last entry in table
add ip, lr, r0, lsl #1 // compute label = lr + element*2
bx ip // jump to computed label