Take the following testcase:
typedef unsigned long long uint64_t;
void f(uint64_t *a, uint64_t aa) __attribute__((noinline));
void f(uint64_t *a, uint64_t aa)
{
uint64_t new_value = aa;
uint64_t old_value = *a;
int bit_size = 32;
uint64_t mask = (uint64_t)(unsigned)(-1);
uint64_t tmp = old_value & mask;
new_value &= mask;
/* On overflow we need to add 1 in the upper bits */
if (tmp > new_value)
new_value += 1ull<<bit_size;
/* Add in the upper bits from the old value */
new_value += old_value & ~mask;
*a = new_value;
}
int main(void)
{
uint64_t value, new_value, old_value;
value = 0x100000001;
old_value = value;
new_value = (value+1)&(uint64_t)(unsigned)(-1);
f(&value, new_value);
if (value != old_value+1)
{
__builtin_printf("FAIL.\n");
__builtin_abort ();
}
__builtin_printf("0x%llx\n",value);
}
--- CUT ---
Combine is able combines the following three instruction:
(insn 8 7 9 2 (set (reg/v:DI 194 [ new_value ])
(and:DI (reg/v:DI 5 $5 [ aa ])
(const_int 4294967295 [0xffffffff]))) t.c:10 152 {*anddi3}
(expr_list:REG_DEAD (reg/v:DI 200 [ aa ])
(nil)))
(insn 9 8 10 2 (set (reg:DI 201)
(and:DI (reg/v:DI 195 [ old_value ])
(const_int 4294967295 [0xffffffff]))) t.c:9 152 {*anddi3}
(nil))
(insn 10 9 11 2 (set (reg:DI 202)
(gtu:DI (reg:DI 201)
(reg/v:DI 194 [ new_value ]))) t.c:12 473 {*sgtu_didi}
(expr_list:REG_DEAD (reg:DI 201)
(nil)))
--- CUT ---
Into:
(set (reg:DI 202)
(ltu:DI (reg:SI 5 $5 [ aa+4 ])
(subreg:SI (reg/v:DI 195 [ old_value ]) 4)))
Which is wrong when TRULY_NOOP_TRUNCATION_MODES_P is false which is
what happens on MIPS.
This patches fixes the problem by change the place where the call to
gen_lowpart should have been gen_lowpart_or_truncate in
simplify_comparison.
OK? Bootstrapped and tested on mips64-linux-gnu with no regressions.
Thanks,
Andrew Pinski
ChangeLog:
* combine.c (simplify_comparison): Use gen_lowpart_or_truncate instead
of gen_lowpart when we had a truncating and.
* gcc.c-torture/execute/20110418-1.c: New testcase.
Index: combine.c
===================================================================
--- combine.c (revision 187203)
+++ combine.c (working copy)
@@ -11199,8 +11199,8 @@ simplify_comparison (enum rtx_code code,
tmode != GET_MODE (op0); tmode = GET_MODE_WIDER_MODE (tmode))
if ((unsigned HOST_WIDE_INT) c0 == GET_MODE_MASK (tmode))
{
- op0 = gen_lowpart (tmode, inner_op0);
- op1 = gen_lowpart (tmode, inner_op1);
+ op0 = gen_lowpart_or_truncate (tmode, inner_op0);
+ op1 = gen_lowpart_or_truncate (tmode, inner_op1);
code = unsigned_condition (code);
changed = 1;
break;
Index: testsuite/gcc.c-torture/execute/20110418-1.c
===================================================================
--- testsuite/gcc.c-torture/execute/20110418-1.c (revision 0)
+++ testsuite/gcc.c-torture/execute/20110418-1.c (revision 0)
@@ -0,0 +1,29 @@
+typedef unsigned long long uint64_t;
+void f(uint64_t *a, uint64_t aa) __attribute__((noinline));
+void f(uint64_t *a, uint64_t aa)
+{
+ uint64_t new_value = aa;
+ uint64_t old_value = *a;
+ int bit_size = 32;
+ uint64_t mask = (uint64_t)(unsigned)(-1);
+ uint64_t tmp = old_value & mask;
+ new_value &= mask;
+ /* On overflow we need to add 1 in the upper bits */
+ if (tmp > new_value)
+ new_value += 1ull<<bit_size;
+ /* Add in the upper bits from the old value */
+ new_value += old_value & ~mask;
+ *a = new_value;
+}
+int main(void)
+{
+ uint64_t value, new_value, old_value;
+ value = 0x100000001;
+ old_value = value;
+ new_value = (value+1)&(uint64_t)(unsigned)(-1);
+ f(&value, new_value);
+ if (value != old_value+1)
+ __builtin_abort ();
+ return 0;
+}
+
