http://llvm.org/bugs/show_bug.cgi?id=10923
Summary: Optimiser problem: shows up in Python's pow()
Product: clang
Version: trunk
Platform: All
OS/Version: All
Status: NEW
Severity: normal
Priority: P
Component: -New Bugs
AssignedTo: [email protected]
ReportedBy: [email protected]
CC: [email protected]
Created an attachment (id=7262)
--> (http://llvm.org/bugs/attachment.cgi?id=7262)
Test program to demonstrate the problem.
The problem showed up when I compiled Python 2.7.2 with Clang-trunk (dated
September 23, 2011), but exactly the same problem occurs for Clang from Xcode
4.2 beta 7 (tags/Apple/clang-211.9).
Running 'python' compiled with clang-3.0-trunk:
>>> 2**63
-9223372036854775808
>>> 2**64
0
Correct results should be:
>>> 2**63
9223372036854775808L
>>> 2**64
18446744073709551616L
When Python is compiled without optimisations (-O0), the problems does not
occur.
I extracted int_pow() function from Python 2.7.2 source code
(Objects/intobject.c) and made a test program (attached as pow.c).
Compiling and running with and without optimisations gives different results:
% clang -Wall -o pow pow.c ; ./pow
case 2: PyLong_Type.tp_as_number->nb_power
0
% clang -Wall -O1 -o pow pow.c ; ./pow
0
The function works correctly after switching types from "long" to "unsigned
long". I guess some operations are optimised out and the condition leading to
"case 2" never happends.
Please, fix. :)
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