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re PR rtl-optimization/3508 (builtin memcmp() could be optimised)

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* builtins.c (expand_builtin_memcmp): Optimize memcmp built-in
        when all arguments are known constant.  Fixes PR opt/3508.

        * gcc.c-torture/execute/string-opt-16.c: New testcase.

From-SVN: r48335
This commit is contained in:
Roger Sayle 2001-12-27 23:34:31 +00:00 committed by Richard Henderson
parent 30d7b5f413
commit fe85f179e8
4 changed files with 68 additions and 0 deletions
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5
gcc/ChangeLog
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@ -1,3 +1,8 @@
2001-12-27 Roger Sayle <roger@eyesopen.com>
* builtins.c (expand_builtin_memcmp): Optimize memcmp built-in
when all arguments are known constant. Fixes PR opt/3508.
2001-12-27 Kazu Hirata <kazu@hxi.com>
* config/h8300/h8300.md (two anonymous patterns): Remove.

14
gcc/builtins.c
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@ -2252,6 +2252,7 @@ expand_builtin_memcmp (exp, arglist, target, mode)
enum machine_mode mode;
{
tree arg1, arg2, len;
const char *p1, *p2;
if (!validate_arglist (arglist,
POINTER_TYPE, POINTER_TYPE, INTEGER_TYPE, VOID_TYPE))
@ -2271,6 +2272,19 @@ expand_builtin_memcmp (exp, arglist, target, mode)
return const0_rtx;
}
p1 = c_getstr (arg1);
p2 = c_getstr (arg2);
/* If all arguments are constant, and the value of len is not greater
than the lengths of arg1 and arg2, evaluate at compile-time. */
if (host_integerp (len, 1) && p1 && p2
&& compare_tree_int (len, strlen (p1)+1) <= 0
&& compare_tree_int (len, strlen (p2)+1) <= 0)
{
const int r = memcmp (p1, p2, tree_low_cst (len, 1));
return (r < 0 ? constm1_rtx : (r > 0 ? const1_rtx : const0_rtx));
}
/* If len parameter is one, return an expression corresponding to
(*(const unsigned char*)arg1 - (const unsigned char*)arg2). */
if (host_integerp (len, 1) && tree_low_cst (len, 1) == 1)

4
gcc/testsuite/ChangeLog
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@ -1,3 +1,7 @@
2001-12-27 Roger Sayle <roger@eyesopen.com>
* gcc.c-torture/execute/string-opt-16.c: New testcase.
2001-12-27 Richard Henderson <rth@redhat.com>
* gcc.dg/debug-1.c, gcc.dg/debug-2.c: New.

45
gcc/testsuite/gcc.c-torture/execute/string-opt-16.c Normal file
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@ -0,0 +1,45 @@
/* Copyright (C) 2001 Free Software Foundation.
Ensure that builtin memcmp operations when all three arguments
are constant is optimized and performs correctly. Taken from
PR optimize/3508.
Written by Roger Sayle, 12/26/2001. */
extern void abort (void);
extern void link_error (void);
typedef __SIZE_TYPE__ size_t;
extern int memcmp (const void *, const void *, size_t);
int
main (int argc)
{
if (memcmp ("abcd", "efgh", 4) >= 0)
link_error ();
if (memcmp ("abcd", "abcd", 4) != 0)
link_error ();
if (memcmp ("efgh", "abcd", 4) <= 0)
link_error ();
return 0;
}
#ifdef __OPTIMIZE__
/* When optimizing, all the above cases should be transformed into
something else. So any remaining calls to the original function
should abort. */
static int
memcmp (const void *s1, const void *s2, size_t len)
{
abort ();
}
#else
/* When not optimizing, the above tests may generate references to
the function link_error, but should never actually call it. */
static void
link_error ()
{
abort ();
}
#endif