38a0cb5201
ARM's UAL syntax allows the same assembly file to be compiled in both ARM and Thumb mode. Conditional execution is handled by requiring the Thumb IT blocks, but essentially ignoring them when compiling for ARM. llvm-svn: 194429
45 lines
1.8 KiB
ArmAsm
45 lines
1.8 KiB
ArmAsm
//===-- switch.S - Implement switch* --------------------------------------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is dual licensed under the MIT and the University of Illinois Open
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// Source Licenses. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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#include "../assembly.h"
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//
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// When compiling switch statements in thumb mode, the compiler
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// can use these __switch* helper functions The compiler emits a blx to
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// the __switch* function followed by a table of displacements for each
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// case statement. On entry, R0 is the index into the table. The __switch*
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// function uses the return address in lr to find the start of the table.
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// The first entry in the table is the count of the entries in the table.
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// It then uses R0 to index into the table and get the displacement of the
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// address to jump to. If R0 is greater than the size of the table, it jumps
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// to the last entry in the table. Each displacement in the table is actually
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// the distance from lr to the label, thus making the tables PIC.
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.text
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.syntax unified
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//
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// The table contains signed byte sized elements which are 1/2 the distance
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// from lr to the target label.
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//
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.align 2
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DEFINE_COMPILERRT_PRIVATE_FUNCTION(__switch8)
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ldrb ip, [lr, #-1] // get first byte in table
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cmp r0, ip // signed compare with index
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ite lo
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ldrsblo r0, [lr, r0] // get indexed byte out of table
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ldrsbhs r0, [lr, ip] // if out of range, use last entry in table
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add ip, lr, r0, lsl #1 // compute label = lr + element*2
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bx ip // jump to computed label
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// tell linker it can break up file at label boundaries
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.subsections_via_symbols
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