http://llvm.org/bugs/show_bug.cgi?id=13991
Bug #: 13991
Summary: llvm.smul.with.overflow overflow detection fails for
63 bit integer width
Product: libraries
Version: 3.1
Platform: PC
OS/Version: MacOS X
Status: NEW
Severity: normal
Priority: P
Component: Common Code Generator Code
AssignedTo: [email protected]
ReportedBy: [email protected]
CC: [email protected]
Classification: Unclassified
According to the documentation at
http://llvm.org/docs/LangRef.html#int_smul_overflow smul.with.overflow should
work for any integer bit width, but for a width of 63 bits there are some cases
where the overflow detection fails.
The following LLVM IR returns 0 instead of 1 in the overflow detection. If I
instead change it to multiplying 2 and 4611686018427387903 it does signal the
overflow in the overflow bit.
declare {i63, i1} @llvm.smul.with.overflow.i63(i63 %a, i63 %b)
define i1 @main() nounwind {
entry:
%res = call {i63, i1} @llvm.smul.with.overflow.i63( i63 4, i63
4611686018427387903 )
%sum = extractvalue {i63, i1} %res, 0
%overflow = extractvalue {i63, i1} %res, 1
ret i1 %overflow
}
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