[all-commits] [llvm/llvm-project] 8c1e52: [AArch64] Adding "armv8.8-a" BC instruction.
Simon Tatham via All-commits
all-commits at lists.llvm.org
Mon Jan 3 04:34:41 PST 2022
Author: Simon Tatham <simon.tatham at arm.com>
Date: 2022-01-03 (Mon, 03 Jan 2022)
[AArch64] Adding "armv8.8-a" BC instruction.
This instruction is described in the Arm A64 Instruction Set
Architecture documentation available here:
FEAT_HBC "Hinted Conditional Branches" is listed in the 2021 A-Profile Architecture Extensions:
'BC.cc', where 'cc' is any ordinary condition code, is an instruction
that looks exactly like B.cc (the normal conditional branch), except
that bit 4 of the encoding is 1 rather than 0, which hints something
to the branch predictor (specifically, that this branch is expected to
be highly consistent, even though _which way_ it will consistently go
is not known at compile time).
This commit introduces a special subtarget feature for HBC, which is a
dependency of the top-level 8.8-A feature, and uses that to enable the
new BC instruction.
Differential Revision: https://reviews.llvm.org/D116156
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