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. */
23 osr_flag_ignore_x86_shift = 2 /**< ignore Multiplications by 2, 4, 8 */
26 /* FirmJNI cannot handle identical enum values... */
28 /** default setting */
29 #define osr_flag_default osr_flag_lftr_with_ov_check
32 * Do the Operator Scalar Replacement optimization and linear
33 * function test replacement for loop control.
35 * @param irg the graph which should be optimized
36 * @param flags one of osr_flags
38 * The linear function replacement test is controlled by the flags.
39 * If the osr_flag_lftr_with_ov_check is set, the replacement is only
40 * done if do overflow can occur.
41 * Otherwise it is ALWAYS done which might be insecure.
45 * for (i = 0; i < 100; ++i)
47 * might be replaced by
49 * for (i = 0; i < 400; i += 4)
53 * for (i = 0; i < 0x7FFFFFFF; ++i)
55 * will not be replaced by
57 * for (i = 0; i < 0xFFFFFFFC; i += 4)
59 * because of overflow.
63 * for (i = 0; i <= 0xF; ++i)
65 * will NOT be transformed into
67 * for (i = 0xFFFFFFF0; i <= 0xFFFFFFFF; ++i)
69 * although here is no direct overflow. The OV occurs when the ++i
70 * is executed (and would created an endless loop here!).
72 * For the same reason, a loop
74 * for (i = 0; i <= 9; i += x)
76 * will NOT be transformed because we cannot estimate whether an overflow
77 * might happen adding x.
79 * Note that i < a + 400 is also not possible with the current implementation
80 * although this might be allowed by other compilers...
82 * Note further that tests for equality can be handled some simplier (but are not
85 * This algorithm destoyes the link field of nodes.
87 void opt_osr(ir_graph *irg, unsigned flags);
89 #endif /* _OPT_OSR_H_ */