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Diffstat (limited to 'compiler-rt/lib/builtins/arm/switch16.S')
| -rw-r--r-- | compiler-rt/lib/builtins/arm/switch16.S | 46 |
1 files changed, 46 insertions, 0 deletions
diff --git a/compiler-rt/lib/builtins/arm/switch16.S b/compiler-rt/lib/builtins/arm/switch16.S new file mode 100644 index 00000000000..0dedc598a13 --- /dev/null +++ b/compiler-rt/lib/builtins/arm/switch16.S @@ -0,0 +1,46 @@ +//===-- switch.S - Implement switch* --------------------------------------===// +// +// The LLVM Compiler Infrastructure +// +// This file is dual licensed under the MIT and the University of Illinois Open +// Source Licenses. 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 signed 2-byte sized elements which are 1/2 the distance +// from lr to the target label. +// + .align 2 +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 + add ip, lr, ip, lsl #1 // compute address of last element in table + ite lo + ldrshlo r0, [r0, #1] // load 16-bit element if r0 is in range + 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 +END_COMPILERRT_FUNCTION(__switch16) + + // tell linker it can break up file at label boundaries + .subsections_via_symbols |
