On Wed, Apr 20, 2016 at 9:55 AM, Richard Biener
<richard.guent...@gmail.com> wrote:
> On Tue, Apr 19, 2016 at 7:00 PM, Bin Cheng <bin.ch...@arm.com> wrote:
>> Hi,
>> Type conversion from integer to smaller unsigned type could be transformed
>> into BIT_AND_EXPR in compilation. For example,
>> int i;
>> for (i = 0; i < n; i++)
>> {
>> unsigned char uc = (unsigned char) i; // transformed into X = i &&
>> 255, in which both X and i are of int type.
>> b[uc] = 0;
>> }
>> X here could a valid SCEV if we can prove that loop doesn't iterate more
>> than 255 times. In other words, if 'i' is SCEV and its value is in the
>> range of representable set of type "unsigned char". This information could
>> be available with -faggressive-loop-optimizations.
>> This patch adds support for BIT_AND_EXPR in scalar evolution to handle such
>> cases, as well as two new tests.
>>
>> Bootstrap and test on x86_64 & AArch64. Is it OK?
>
> Don't use cst_and_fits_in_hwi/int_cst_value - those are odd beasts.
> Use tree_fits_uhwi_p / tree_to_uhwi.
> Or just use wi::popcount and verify it against wi::clz.
Thanks for reviewing, here is the updated patch. Regtest ongoing,
shouldn't be any surprise though. Is it OK?
Thanks,
bin
>
> Richard.
>
>> Thanks,
>> bin
>>
>> 2016-03-24 Bin Cheng <bin.ch...@arm.com>
>>
>> * tree-scalar-evolution.c (interpret_rhs_expr): Handle BIT_AND_EXPR.
>>
>> gcc/testsuite/ChangeLog
>> 2016-03-24 Bin Cheng <bin.ch...@arm.com>
>>
>> * gcc.dg/tree-ssa/scev-11.c: New test.
>> * gcc.dg/tree-ssa/scev-12.c: New test.
>>
diff --git a/gcc/tree-scalar-evolution.c b/gcc/tree-scalar-evolution.c
index 88a0eaa..d6f2a2f 100644
--- a/gcc/tree-scalar-evolution.c
+++ b/gcc/tree-scalar-evolution.c
@@ -1937,6 +1937,36 @@ interpret_rhs_expr (struct loop *loop, gimple *at_stmt,
res = chrec_convert (type, chrec1, at_stmt);
break;
+ case BIT_AND_EXPR:
+ /* Given int variable A, handle A&0xffff as (int)(unsigned short)A.
+ If A is SCEV and its value is in the range of representable set
+ of type unsigned short, the result expression is a (no-overflow)
+ SCEV. */
+ res = chrec_dont_know;
+ if (tree_fits_uhwi_p (rhs2))
+ {
+ int precision;
+ unsigned HOST_WIDE_INT val = tree_to_uhwi (rhs2);
+
+ val ++;
+ /* Skip if value of rhs2 wraps in unsigned HOST_WIDE_INT or
+ it's not the maximum value of a smaller type than rhs1. */
+ if (val != 0
+ && (precision = exact_log2 (val)) > 0
+ && (unsigned) precision < TYPE_PRECISION (TREE_TYPE (rhs1)))
+ {
+ tree utype = build_nonstandard_integer_type (precision, 1);
+
+ if (TYPE_PRECISION (utype) < TYPE_PRECISION (TREE_TYPE (rhs1)))
+ {
+ chrec1 = analyze_scalar_evolution (loop, rhs1);
+ chrec1 = chrec_convert (utype, chrec1, at_stmt);
+ res = chrec_convert (TREE_TYPE (rhs1), chrec1, at_stmt);
+ }
+ }
+ }
+ break;
+
default:
res = chrec_dont_know;
break;
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/scev-11.c
b/gcc/testsuite/gcc.dg/tree-ssa/scev-11.c
new file mode 100644
index 0000000..a7181b2
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/scev-11.c
@@ -0,0 +1,28 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-ivopts-details" } */
+
+int a[128];
+extern int b[];
+
+int bar (int *);
+
+int
+foo (int n)
+{
+ int i;
+
+ for (i = 0; i < n; i++)
+ {
+ unsigned char uc = (unsigned char)i;
+ a[i] = i;
+ b[uc] = 0;
+ }
+
+ bar (a);
+ return 0;
+}
+
+/* Address of array reference to b is scev. */
+/* { dg-final { scan-tree-dump-times "use \[0-9\]\n address" 2 "ivopts" } } */
+
+
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/scev-12.c
b/gcc/testsuite/gcc.dg/tree-ssa/scev-12.c
new file mode 100644
index 0000000..6915ba8
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/scev-12.c
@@ -0,0 +1,30 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-ivopts-details" } */
+
+int a[128];
+extern int b[];
+
+int bar (int *);
+
+int
+foo (int x, int n)
+{
+ int i;
+
+ for (i = 0; i < n; i++)
+ {
+ unsigned char uc = (unsigned char)i;
+ if (x)
+ a[i] = i;
+ b[uc] = 0;
+ }
+
+ bar (a);
+ return 0;
+}
+
+/* Address of array reference to b is not scev. */
+/* { dg-final { scan-tree-dump-times "use \[0-9\]\n address" 1 "ivopts" } } */
+
+
+
