https://bugs.llvm.org/show_bug.cgi?id=39861
Bug ID: 39861
Summary: Incorrect fold of 'x & (-1 >> y) s>= x'
Product: libraries
Version: trunk
Hardware: All
OS: All
Status: NEW
Keywords: miscompilation
Severity: normal
Priority: P
Component: Scalar Optimizations
Assignee: [email protected]
Reporter: [email protected]
CC: [email protected], [email protected],
[email protected], [email protected]
This is a bug in
test/Transforms/InstCombine/canonicalize-constant-low-bit-mask-and-icmp-sge-to-icmp-sle.ll
Output of Alive2:
declare i1 @pv(i8 %x, i8 %y) {
%tmp0 = lshr i8 255, %y
%tmp1 = and i8 %tmp0, %x
%ret = icmp sge i8 %tmp1, %x
ret i1 %ret
}
=>
declare i1 @pv(i8 %x, i8 %y) {
%tmp0 = lshr i8 255, %y
%1 = icmp sge i8 %tmp0, %x
ret i1 %1
}
Transformation doesn't verify!
ERROR: Value mismatch
Example:
i8 %x = 0x7e (126)
i8 %y = 0x0 (0)
Source:
i8 %tmp0 = 0xff (255, -1)
i8 %tmp1 = 0x7e (126)
i1 %ret = 0x1 (1, -1)
Target:
i8 %tmp0 = 0xff (255, -1)
i1 %1 = 0x0 (0)
Source value: 0x1 (1, -1)
Target value: 0x0 (0)
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