2b75ff192d
This reverts commit cf002847a464c004a57ca4777251b1aafc33d958 i.e.,
relands ba603b5e4d44f1a25207a2a00196471d2ba93424. It was reverted
because it was subtly wrong: multiplying an uninitialized zero should
not result in an initialized zero.
This reland fixes the issue by using instrumentation analogous to
visitAnd (bitwise AND of an initialized zero and an uninitialized value
results in an initialized value). Additionally, this reland expands a
test case; fixes the commit message; and optimizes the change to avoid
the need for horizontalReduce.
The current instrumentation has false positives: it does not take into
account that multiplying an initialized zero value with an uninitialized
value results in an initialized zero value This change fixes the issue
during the multiplication step. The horizontal add step is modeled using
bitwise OR.
Future work can apply this improved handler to the AVX512 equivalent
intrinsics (x86_avx512_pmaddw_d_512, x86_avx512_pmaddubs_w_512.) and AVX
VNNI intrinsics.
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