44 lines
1.7 KiB
ArmAsm
44 lines
1.7 KiB
ArmAsm
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//===-- 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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ldrsbcc 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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