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      1 //===-- switch.S - Implement switch* --------------------------------------===//
      2 //
      3 //                     The LLVM Compiler Infrastructure
      4 //
      5 // This file is distributed under the University of Illinois Open Source
      6 // License. See LICENSE.TXT for details.
      7 //
      8 //===----------------------------------------------------------------------===//
      9 
     10 #include "../assembly.h"
     11 
     12 //
     13 // When compiling switch statements in thumb mode, the compiler
     14 // can use these __switch* helper functions  The compiler emits a blx to
     15 // the __switch* function followed by a table of displacements for each
     16 // case statement.  On entry, R0 is the index into the table. The __switch*
     17 // function uses the return address in lr to find the start of the table.
     18 // The first entry in the table is the count of the entries in the table.
     19 // It then uses R0 to index into the table and get the displacement of the
     20 // address to jump to.  If R0 is greater than the size of the table, it jumps
     21 // to the last entry in the table. Each displacement in the table is actually
     22 // the distance from lr to the label, thus making the tables PIC.
     23 
     24 
     25 	.text
     26 	.syntax unified
     27 
     28 //
     29 // The table contains signed 4-byte sized elements which are the distance
     30 // from lr to the target label.
     31 //
     32 DEFINE_COMPILERRT_PRIVATE_FUNCTION(__switch32)
     33 	ldr     ip, [lr, #-1]            // get first 32-bit word in table
     34 	cmp     r0, ip                   // compare with index
     35 	add     r0, lr, r0, lsl #2       // compute address of element in table
     36 	ldrcc   r0, [r0, #3]             // load 32-bit element if r0 is in range
     37 	add     ip, lr, ip, lsl #2       // compute address of last element in table
     38 	ldrcs   r0, [ip, #3]             // load 32-bit element if r0 out of range
     39 	add     ip, lr, r0               // compute label = lr + element
     40 	bx      ip                       // jump to computed label
     41 
     42 
     43 	// tell linker it can break up file at label boundaries
     44 	.subsections_via_symbols
     45 
     46