[Bug tree-optimization/47061] VRP doesn't propagate through x<<=1, but it does for x*=2

[zsojka at seznam dot cz]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47061

--- Comment #1 from Zdenek Sojka <zsojka at seznam dot cz> 2010-12-24 15:54:35 
UTC ---
Created attachment 22851
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=22851
another testcase

This testcase seems to be optimised at the RTL level.

$ gcc pr47061-2.c -S -O3 -fdump-tree-vrp

.vrp1/2 dumps show:
...
c_1(D): VARYING
D.2684_2: [-128, 127]
i_3: VARYING
D.2685_4: [0, 1]
...
<bb 2>:
  D.2684_2 = (int) c_1(D);
  i_3 = D.2684_2 << 1;
  D.2685_4 = i_3 > 1000;
  return D.2685_4;
...

So the value is known before the shift as well. For the right shift, the
function is optimised correctly.