forked from OSchip/llvm-project
88 lines
3.7 KiB
ArmAsm
88 lines
3.7 KiB
ArmAsm
//===-- switch.S - Implement switch* --------------------------------------===//
|
|
//
|
|
// The LLVM Compiler Infrastructure
|
|
//
|
|
// This file is distributed under the University of Illinois Open Source
|
|
// License. See LICENSE.TXT for details.
|
|
//
|
|
//===----------------------------------------------------------------------===//
|
|
|
|
#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.
|
|
|
|
|
|
.text
|
|
.syntax unified
|
|
|
|
//
|
|
// The table contains unsigned byte sized elements which are 1/2 the distance
|
|
// from lr to the target label.
|
|
//
|
|
DEFINE_COMPILERRT_PRIVATE_FUNCTION(__switchu8)
|
|
ldrb ip, [lr, #-1] // get first byte in table
|
|
cmp r0, ip // compare with index
|
|
ldrbcc 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
|
|
|
|
|
|
|
|
//
|
|
// The table contains signed byte sized elements which are 1/2 the distance
|
|
// from lr to the target label.
|
|
//
|
|
DEFINE_COMPILERRT_PRIVATE_FUNCTION(__switch8)
|
|
ldrb ip, [lr, #-1] // get first byte in table
|
|
cmp r0, ip // signed compare with index
|
|
ldrsbcc r0, [lr, r0] // get indexed byte out of table
|
|
ldrsbhs 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
|
|
|
|
|
|
//
|
|
// The table contains signed 2-byte sized elements which are 1/2 the distance
|
|
// from lr to the target label.
|
|
//
|
|
DEFINE_COMPILERRT_PRIVATE_FUNCTION(__switch16)
|
|
ldrh ip, [lr, #-1] // get first 16-bit word in table
|
|
cmp r0, ip // compare with index
|
|
add r0, lr, r0, lsl #1 // compute address of element in table
|
|
ldrshcc r0, [r0, #1] // load 16-bit element if r0 is in range
|
|
add ip, lr, ip, lsl #1 // compute address of last element in table
|
|
ldrshhs r0, [ip, #1] // load 16-bit element if r0 out of range
|
|
add ip, lr, r0, lsl #1 // compute label = lr + element*2
|
|
bx ip // jump to computed label
|
|
|
|
|
|
//
|
|
// The table contains signed 4-byte sized elements which are the distance
|
|
// from lr to the target label.
|
|
//
|
|
DEFINE_COMPILERRT_PRIVATE_FUNCTION(__switch32)
|
|
ldr ip, [lr, #-1] // get first 32-bit word in table
|
|
cmp r0, ip // compare with index
|
|
add r0, lr, r0, lsl #2 // compute address of element in table
|
|
ldrcc r0, [r0, #3] // load 32-bit element if r0 is in range
|
|
add ip, lr, ip, lsl #2 // compute address of last element in table
|
|
ldrcs r0, [ip, #3] // load 32-bit element if r0 out of range
|
|
add ip, lr, r0 // compute label = lr + element
|
|
bx ip // jump to computed label
|
|
|
|
|
|
// tell linker it can break up file at label boundaries
|
|
.subsections_via_symbols
|
|
|