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ARM is the only architecture that has a helper function that returns
an unbiased result. This fix is trivial enough that we can show it
doesn't effect any of the other arches. Can we consider this a
regression fix since it used to work until the helper was added :}
Tested with no regressions on x86_64-pc-linux-gnu and arm-none-eabi.
Cheers,
Carlos.
--
Carlos O'Donell
CodeSourcery
carlos@codesourcery.com
(650) 331-3385 x716
gcc/
2006-01-27 Carlos O'Donell <carlos@codesourcery.com>
* optabs.c (prepare_cmp_insn): If unbaised and unsigned then bias
the comparison routine return.
gcc/testsuite/
2006-01-27 Carlos O'Donell <carlos@codesourcery.com>
* gcc.dg/unsigned-long-compare.c: New test.
Index: gcc/optabs.c
===================================================================
--- 1/gcc/optabs.c (revision 110300)
+++ 2/gcc/optabs.c (working copy)
@@ -3711,18 +3711,24 @@
result = emit_library_call_value (libfunc, NULL_RTX, LCT_CONST_MAKE_BLOCK,
word_mode, 2, x, mode, y, mode);
+ /* There are two kinds of comparison routines. Biased routines
+ return 0/1/2, and unbiased routines return -1/0/1. Other parts
+ of gcc expect that the comparison operation is equivalent
+ to the modified comparison. For signed comparisons compare the
+ result against 1 in the unbiased case, and zero in the biased
+ case. For unsigned comparisons always compare against 1 after
+ biasing the unbased result by adding 1. This gives us a way to
+ represent LTU. */
*px = result;
*pmode = word_mode;
- if (TARGET_LIB_INT_CMP_BIASED)
- /* Integer comparison returns a result that must be compared
- against 1, so that even if we do an unsigned compare
- afterward, there is still a value that can represent the
- result "less than". */
- *py = const1_rtx;
- else
+ *py = const1_rtx;
+
+ if (!TARGET_LIB_INT_CMP_BIASED)
{
- *py = const0_rtx;
- *punsignedp = 1;
+ if (*punsignedp)
+ *px = plus_constant (result, 1);
+ else
+ *py = const0_rtx;
}
return;
}
Index: gcc/testsuite/gcc.dg/unsigned-long-compare.c
===================================================================
--- 1/gcc/testsuite/gcc.dg/unsigned-long-compare.c (revision 0)
+++ 2/gcc/testsuite/gcc.dg/unsigned-long-compare.c (revision 0)
@@ -0,0 +1,24 @@
+/* Copyright (C) 2006 Free Software Foundation, Inc. */
+/* Contributed by Carlos O'Donell on 2006-01-27 */
+
+/* Test a division corner case where the expression simplifies
+ to a comparison, and the optab expansion is wrong. The optab
+ expansion emits a function whose return is unbiased and needs
+ adjustment. */
+/* Origin: Carlos O'Donell <carlos@codesourcery.com> */
+/* { dg-do run { target arm-*-*eabi* } } */
+/* { dg-options "" } */
+#include <stdlib.h>
+
+#define BIG_CONSTANT 0xFFFFFFFF80000000ULL
+
+int main (void)
+{
+ unsigned long long OneULL = 1ULL;
+ unsigned long long result;
+
+ result = OneULL / BIG_CONSTANT;
+ if (result)
+ abort ();
+ exit (0);
+}
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