3 * File name: ir/opt/opt_osr.h
4 * Purpose: Operator Strength Reduction,
5 * Keith D. Cooper, L. Taylor Simpson, Christopher A. Vick
10 * Copyright: (c) 2006 Universität Karlsruhe
11 * Licence: This file protected by GPL - GNU GENERAL PUBLIC LICENSE.
16 #include "firm_types.h"
18 /** Possible flags for the Operator Scalar Replacement. */
19 typedef enum osr_flags {
20 osr_flag_none = 0, /**< no additional flags */
21 osr_flag_lftr_with_ov_check = 1, /**< do linear function test replacement
22 only if no overflow can occur. */
25 /* FirmJNI cannot handle identical enum values... */
27 /** default setting */
28 #define osr_flag_default osr_flag_lftr_with_ov_check
31 * Do the Operator Scalar Replacement optimization and linear
32 * function test replacement for loop control.
34 * @param irg the graph which should be optimized
35 * @param flags one of osr_flags
37 * The linear function replacement test is controlled by the flags.
38 * If the osr_flag_lftr_with_ov_check is set, the replacement is only
39 * done if do overflow can occur.
40 * Otherwise it is ALWAYS done which might be insecure.
44 * for (i = 0; i < 100; ++i)
46 * might be replaced by
48 * for (i = 0; i < 400; i += 4)
52 * for (i = 0; i < 0x7FFFFFFF; ++i)
54 * will not be replaced by
56 * for (i = 0; i < 0xFFFFFFFC; i += 4)
58 * because of overflow.
62 * for (i = 0; i <= 0xF; ++i)
64 * will NOT be transformed into
66 * for (i = 0xFFFFFFF0; i <= 0xFFFFFFFF; ++i)
68 * although here is no direct overflow. The OV occurs when the ++i
69 * is executed (and would created an endless loop here!).
71 * For the same reason, a loop
73 * for (i = 0; i <= 9; i += x)
75 * will NOT be transformed because we cannot estimate whether an overflow
76 * might happen adding x.
78 * Note that i < a + 400 is also not possible with the current implementation
79 * although this might be allowed by other compilers...
81 * Note further that tests for equality can be handled some simplier (but are not
84 * This algorithm destoyes the link field of nodes.
86 void opt_osr(ir_graph *irg, unsigned flags);
88 #endif /* _OPT_OSR_H_ */