[Bug tree-optimization/106884] New: ifcombine may move shift so it shifts more than bitwidth
kristerw at gcc dot gnu.org
gcc-bugzilla@gcc.gnu.org
Thu Sep 8 00:20:48 GMT 2022
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106884
Bug ID: 106884
Summary: ifcombine may move shift so it shifts more than
bitwidth
Product: gcc
Version: 13.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: kristerw at gcc dot gnu.org
Target Milestone: ---
The function foo from gcc.dg/tree-ssa/ssa-ifcombine-1.c can be called
as foo(1, 1, 33) without invoking undefined behavior
int foo (int x, int a, int b)
{
int c = 1 << a;
if (x & c)
if (x & (1 << b))
return 2;
return 0;
}
But ifcombine transforms this to
int foo (int x, int a, int b)
{
int c;
int _4;
int _10;
int _11;
int _12;
int _13;
<bb 2>:
_10 = 1 << b_8(D);
_11 = 1 << a_5(D);
_12 = _10 | _11;
_13 = x_7(D) & _12;
if (_12 == _13)
goto <bb 3>;
else
goto <bb 4>;
<bb 3>:
<bb 4>:
# _4 = PHI <2(3), 0(2)>
return _4;
}
and this will now calculate 1 << 33 unconditionally for _10.
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