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The Quick compiler and verifier sometimes disagree on dalvik
register types (fp/core/ref) for 0/null constants and merged
registers involving 0/null constants. Since the verifier is
more lenient it can mark a register as a reference for GC
where Quick considers it a floating point register or a dead
register (which would have a ref/fp conflict if not dead).
If the compiler used an fp register to hold the zero value,
the core register or stack location used by GC based on the
verifier data can hold an invalid value.
Previously, as a workaround we stored the fp zero value also
in the stack location or core register where GC would look
for it. This wasn't precise and may have missed some cases.
To fix this properly, we now generate GC maps based on the
compiler's notion of references if register promotion is
enabled.
Bug: https://code.google.com/p/android/issues/detail?id=147187
Change-Id: Id3a2f863b16bdb8969df7004c868773084aec421
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The lack of typing for dex byte code instructions causes problems
for the Quick compiler's register allocation scheme. In Quick,
Dalvik virtual registers can have multiple "home locations" depending
on type. Because CONST operators are untyped and their result can
be used in multiple type contexts, the code generator must ensure
that any CONST #0 definitions of potential floating point uses
are also flushed to the associated reference view for the vreg
(if it exists) to support GC. Previously, this issue was believed
to have been fixed by c/255389 (see internal b/7250540).
However, the earlier fix failed to account for const definitions
propogating to other vregs via MOVE. This CL addresses that case by
applying the earlier workaround to MOVE operators.
Note that there are a few other places where we attempt to deal
with this general problem. First, the verifier will disable
compilation for dex code sequences which have type mismatches on non-const
operations. Second, during vreg analysis we detect type mismatches on
Phi insertion, and disable register promotion if there is a mismatch.
b.android.com/147187
Change-Id: I70f27a59e6f84a89777db91ceacaa94a42f5e952
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