Restrict this transformation to equality conditions.
This transformation is not correct for not-equal conditions:
(trunc x) != C1 & (and x, CA) != C2 -> (and x, CA|CMAX) != C1|C2
Let
C1 == 0
C2 == 0
CA == 0xFF0000
CMAX == 0xFF
and truncating to i8.
The original truth table:
x | A: trunc x != 0 | B: x & 0xFF0000 != 0 | A & B != 0
--------------------------------------------------------------
0x00000 | 0 | 0 | 0
0x00001 | 1 | 0 | 0
0x10000 | 0 | 1 | 0
0x10001 | 1 | 1 | 1
The truth table of the replacement:
x | x & 0xFF00FF != 0
----------------------------
0x00000 | 0
0x00001 | 1
0x10000 | 1
0x10001 | 1
So they are different.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@151691 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed