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backport: re PR tree-optimization/56051 (Wrong expression evaluation) 

Backported from mainline
	2013-01-21  Jakub Jelinek  <jakub@redhat.com>

	PR tree-optimization/56051
	* fold-const.c (fold_binary_loc): Don't fold
	X < (cast) (1 << Y) into (X >> Y) != 0 if cast is either
	a narrowing conversion, or widening conversion from signed
	to unsigned.

	* gcc.c-torture/execute/pr56051.c: New test.

From-SVN: r195658
This commit is contained in:
Jakub Jelinek 2013-02-01 15:11:46 +01:00 committed by Jakub Jelinek
parent 920debdb12
commit daded9451f
4 changed files with 57 additions and 0 deletions
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8
gcc/ChangeLog
View File

@ -1,6 +1,14 @@
2013-02-01 Jakub Jelinek <jakub@redhat.com>
Backported from mainline
2013-01-21 Jakub Jelinek <jakub@redhat.com>
PR tree-optimization/56051
* fold-const.c (fold_binary_loc): Don't fold
X < (cast) (1 << Y) into (X >> Y) != 0 if cast is either
a narrowing conversion, or widening conversion from signed
to unsigned.
2013-01-18 Jakub Jelinek <jakub@redhat.com>
PR middle-end/56015

12
gcc/fold-const.c
View File

@ -13453,10 +13453,22 @@ fold_binary_loc (location_t loc,
TREE_OPERAND (arg1, 1)),
build_int_cst (TREE_TYPE (arg0), 0));
/* Similarly for X < (cast) (1 << Y). But cast can't be narrowing,
otherwise Y might be >= # of bits in X's type and thus e.g.
(unsigned char) (1 << Y) for Y 15 might be 0.
If the cast is widening, then 1 << Y should have unsigned type,
otherwise if Y is number of bits in the signed shift type minus 1,
we can't optimize this. E.g. (unsigned long long) (1 << Y) for Y
31 might be 0xffffffff80000000. */
if ((code == LT_EXPR || code == GE_EXPR)
&& TYPE_UNSIGNED (TREE_TYPE (arg0))
&& CONVERT_EXPR_P (arg1)
&& TREE_CODE (TREE_OPERAND (arg1, 0)) == LSHIFT_EXPR
&& (TYPE_PRECISION (TREE_TYPE (arg1))
>= TYPE_PRECISION (TREE_TYPE (TREE_OPERAND (arg1, 0))))
&& (TYPE_UNSIGNED (TREE_TYPE (TREE_OPERAND (arg1, 0)))
|| (TYPE_PRECISION (TREE_TYPE (arg1))
== TYPE_PRECISION (TREE_TYPE (TREE_OPERAND (arg1, 0)))))
&& integer_onep (TREE_OPERAND (TREE_OPERAND (arg1, 0), 0)))
{
tem = build2 (RSHIFT_EXPR, TREE_TYPE (arg0), arg0,

5
gcc/testsuite/ChangeLog
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@ -1,6 +1,11 @@
2013-02-01 Jakub Jelinek <jakub@redhat.com>
Backported from mainline
2013-01-21 Jakub Jelinek <jakub@redhat.com>
PR tree-optimization/56051
* gcc.c-torture/execute/pr56051.c: New test.
2013-01-18 Jakub Jelinek <jakub@redhat.com>
PR middle-end/56015

32
gcc/testsuite/gcc.c-torture/execute/pr56051.c Normal file
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@ -0,0 +1,32 @@
/* PR tree-optimization/56051 */
extern void abort (void);
int
main ()
{
unsigned char x1[1] = { 0 };
unsigned int s1 = __CHAR_BIT__;
int a1 = x1[0] < (unsigned char) (1 << s1);
unsigned char y1 = (unsigned char) (1 << s1);
int b1 = x1[0] < y1;
if (a1 != b1)
abort ();
#if __SIZEOF_LONG_LONG__ > __SIZEOF_INT__
unsigned long long x2[1] = { 2ULL << (sizeof (int) * __CHAR_BIT__) };
unsigned int s2 = sizeof (int) * __CHAR_BIT__ - 1;
int a2 = x2[0] >= (unsigned long long) (1 << s2);
unsigned long long y2 = 1 << s2;
int b2 = x2[0] >= y2;
if (a2 != b2)
abort ();
unsigned long long x3[1] = { 2ULL << (sizeof (int) * __CHAR_BIT__) };
unsigned int s3 = sizeof (int) * __CHAR_BIT__ - 1;
int a3 = x3[0] >= (unsigned long long) (1U << s3);
unsigned long long y3 = 1U << s3;
int b3 = x3[0] >= y3;
if (a3 != b3)
abort ();
#endif
return 0;
}