http://llvm.org/bugs/show_bug.cgi?id=20832
Bug ID: 20832
Summary: APFloat::fusedMultiplyAdd is broken when addend is 0
Product: libraries
Version: trunk
Hardware: All
OS: All
Status: NEW
Severity: normal
Priority: P
Component: Support Libraries
Assignee: [email protected]
Reporter: [email protected]
CC: [email protected]
Classification: Unclassified
I believe the following testcase demonstrates a bug in
APFloat::fusedMultiplyAdd. I would expect this to produce a result of 56
((7*8)+0) but instead it produces 7. The addend being 0 seems to be the key.
----------------------------------------------------------------------
declare double @llvm.fma.f64(double, double, double) nounwind
define double @_Z4testv() nounwind {
%1 = call double @llvm.fma.f64(double 7.000000e+00, double 8.000000e+00,
double 0.000000e+00)
ret double %1
}
----------------------------------------------------------------------
Using r216885:
llc test.ll -mtriple=x86_64-unknown-unknown -o -
we get the following constant generated:
.quad 4619567317775286272 # double 7
Within the function APFloat::fusedMultiplyAdd it calls multiplySpecials which
returns opOK allowing the call to addOrSubtract to occur, however at no point
is the actual multiplication performed, meaning that we essentially do 7+0,
ignoring the multiplicand entirely.
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