http://llvm.org/bugs/show_bug.cgi?id=21243
Bug ID: 21243
Summary: InstCombiner::commonIDivTransforms: incorrect
transformation
Product: libraries
Version: trunk
Hardware: All
OS: All
Status: NEW
Severity: normal
Priority: P
Component: Scalar Optimizations
Assignee: [email protected]
Reporter: [email protected]
CC: [email protected]
Classification: Unclassified
One transformation done in InstCombiner::commonIDivTransforms()
(InstCombineMulDivRem.cpp) is incorrect:
(X / C1) / C2 -> 0
if C1*C2 overflows
In the following counterexample, we can see that even C1*C2 overflows (it does,
the result would be = 2), the final result may be non-zero.
----------------------------------------
Pre: !WillNotOverflowSignedMul(C1, C2)
%Op0 = sdiv %X, C1
%r = sdiv %Op0, C2
=>
%r = 0
Done: 1
ERROR: Mismatch in values of i2 %r
Example:
%X i2 = 2 (0x2)
C1 i2 = 2 (0x2)
C2 i2 = 3 (0x3)
%Op0 i2 = 1 (0x1)
Source value: 3 (0x3)
Target value: 0 (0x0)
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