This patch adds support to the instruction-referencing LiveDebugValues
implementation for emitting entry values. The instruction referencing
implementations tracking by value rather than location means that we can
get around two of the issues with VarLocs. DBG_VALUE instructions that
re-assign the same value to a variable are no longer a problem, because we
can "see through" to the value being assigned. We also don't need to do
anything special during the dataflow stages: the "variable value problem"
doesn't need to know whether a value is available most of the time, and the
times it deoes need to know are always when entry values need to be
terminated.
The patch modifies the "TransferTracker" class, adding methods to identify
when a variable ias an entry value candidate, and when a machine value is
an entry value. recoverAsEntryValue tests these two things and emits an
entry-value expression if they're true. It's used when we clobber or
otherwise lose a value and can't find a replacement location for the value
it contained.
Differential Revision: https://reviews.llvm.org/D88406
Debug entry values functionality provides debug information about
call sites and function parameters values at the call entry spot.
Condition for generating this type of information is
compiling with -g option and optimization level higher
than zero(-O0).
In ISEL phase, while lowering call instructions, collect info
about registers that forward arguments into following
function frame. We store such info into MachineFunction of
the caller function. This is used very late, when dumping DWARF
info about call site parameters.
The call site info is visible at MIR level, as callSites attribute
of MachineFunction. Also, when using unmodified parameter value
inside callee it could be described as DW_OP_entry_value expression.
To deal with callSites attribute, we should pass
-emit-call-site-info option to llc.
This patch enables functionality in clang frontend and adds
call site info generation support for MIPS targets
(mips, mipsel, mips64, mips64el).
Patch by Nikola Tesic
Differential Revision: https://reviews.llvm.org/D78105
Jeremy Morse