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Diffstat (limited to 'lib/builtins/arm/switch32.S')
| -rw-r--r-- | lib/builtins/arm/switch32.S | 47 |
1 files changed, 47 insertions, 0 deletions
diff --git a/lib/builtins/arm/switch32.S b/lib/builtins/arm/switch32.S new file mode 100644 index 000000000..64d558eb8 --- /dev/null +++ b/lib/builtins/arm/switch32.S @@ -0,0 +1,47 @@ +//===-- 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 4-byte sized elements which are the distance +// from lr to the target label. +// + .align 2 +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 + add ip, lr, ip, lsl #2 // compute address of last element in table + ite lo + ldrlo r0, [r0, #3] // load 32-bit element if r0 is in range + ldrhs 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 +END_COMPILERRT_FUNCTION(__switch32) + + // tell linker it can break up file at label boundaries + .subsections_via_symbols + |