The node was introduced in 59c39dc1 and was intended to allow writing patterns like this: `[(set AL, (mul AL, GR8:$src1)), (implicit EFLAGS)]` However, it does not introduce new functionality because the same pattern can be equivalently expressed as: `[(set AL, EFLAGS, (mul AL, GR8:$src1))]` The latter form is also more flexible as it allows reordering output operands. In most places uses of `implicit` were redundant -- removing them didn't change anything in the generated DAG tables. The only three cases where it did have effect are in X86InstrArithmetic.td and X86InstrSystem.td -- those were rewritten to use `set` node. Removing `implicit` from some patterns made them importable by GISel, hence the change in a test.
Ref.: https://cdrdv2.intel.com/v1/dl/getContent/671368
Spec reference: https://cdrdv2.intel.com/v1/dl/getContent/678938
Extended VMX instructions and 8 bit apx extended instructions don't need W bit, they are marked as W ignored in spec. RFC: https://discourse.llvm.org/t/rfc-design-for-apx-feature-egpr-and-ndd-support/73031/4
VERR/VERW instructions will define ZF flag.
[@xia0ji233](https://github.com/xia0ji233) and I found that X86::LAR and
X86::lSR implicit use eflags register. However, it was not been defined
in LLVM, which means we will get wrong alive-result if we use these two
instructions.
R16-R31 was added into GPRs in https://github.com/llvm/llvm-project/pull/70958, This patch supports the promoted ENQCMD, KEYLOCKER and USER-MSR instructions in EVEX space. RFC: https://discourse.llvm.org/t/rfc-design-for-apx-feature-egpr-and-ndd-support/73031/4
R16-R31 was added into GPRs in https://github.com/llvm/llvm-project/pull/70958, This patch supports the lowering for promoted SHA/MOVDIR/CRC32/INVPCID/CET. RFC: https://discourse.llvm.org/t/rfc-design-for-apx-feature-egpr-and-ndd-support/73031/4
It helps simplify the class definitions. Now, the only explicit usage of PS is to check prefix 0x66/0xf2/0xf3 can not be used a prefix, e.g. wbinvd. See 82974e0114f02ffc07557e217d87f8dc4e100a26 for more details.