This patch reduces the time taken for clang to compile the generated
disassembler for an out-of-tree target with InsnType bigger than 64 bits
from 4m30s to 48s.
D67686 did a similar thing for CodeEmitterGen.
The idea is to tweak the API of the APInt-like InsnType class so that
we don't need so many temporary InsnTypes. This takes advantage of the
rule stated in D52100 that currently "no string of bits extracted
from the encoding may exceeed 64-bits", so we can use uint64_t for some
temporaries.
D52100 goes on to say that "fields are still permitted to exceed 64-bits
so long as they aren't one contiguous string of bits". This patch breaks
that by always using a "uint64_t tmp" in the generated decodeToMCInst,
but it should be easy to fix in FilterChooser::emitBinaryParser by
choosing to use a different type of tmp based on the known total field
width.
Differential Revision: https://reviews.llvm.org/D98046
Summary:
The problem:
When an operand had bits explicitly set to "1" (as in the InitValue.td test case attached), the decoder was ignoring those bits, and the DecoderMethod was receiving an input where the bits were still zero.
The solution:
We added an "InitValue" variable that stores the initial value of the operand based on what bits were explicitly initialized to 1 in TableGen code. The generated decoder code then uses that initial value to initialize the "tmp" variable, then calls fieldFromInstruction to read the values for the remaining bits that were left unknown in TableGen.
This is mainly useful when there are variations of an instruction that differ based on what bits are set in the operands, since this change makes it possible to access those bits in a DecoderMethod. The DecoderMethod can use those bits to know how to handle the input.
Patch by Nicolas Guillemot
Reviewers: craig.topper, dsanders, fhahn
Reviewed By: dsanders
Subscribers: llvm-commits
Differential Revision: https://reviews.llvm.org/D63741
llvm-svn: 368458
Jay Foad