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cranelift: Remove redundant branch and select instructions (#5097)

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As discussed in the 2022/10/19 meeting, this PR removes many of the branch and select instructions that used iflags, in favor if using brz/brnz and select in their place. Additionally, it reworks selectif_spectre_guard to take an i8 input instead of an iflags input.

For reference, the removed instructions are: br_icmp, brif, brff, trueif, trueff, and selectif.
This commit is contained in:
Trevor Elliott
2022-10-24 16:14:35 -07:00
committed by GitHub
parent 30589170b4
commit ec12415b1f
40 changed files with 579 additions and 2527 deletions
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35
cranelift/codegen/src/simple_preopt.rs
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@@ -469,7 +469,6 @@ fn do_divrem_transformation(divrem_info: &DivRemByConstInfo, pos: &mut FuncCurso
enum BranchOrderKind {
BrzToBrnz(Value),
BrnzToBrz(Value),
InvertIcmpCond(IntCC, Value, Value),
}
/// Reorder branches to encourage fallthroughs.
@@ -538,27 +537,6 @@ fn branch_order(pos: &mut FuncCursor, cfg: &mut ControlFlowGraph, block: Block,
kind,
)
}
InstructionData::BranchIcmp {
opcode: Opcode::BrIcmp,
cond,
destination: cond_dest,
args: ref prev_args,
} => {
let (x_arg, y_arg) = {
let args = pos.func.dfg.inst_args(prev_inst);
(args[0], args[1])
};
(
inst,
args.clone(),
destination,
prev_inst,
prev_args.clone(),
*cond_dest,
BranchOrderKind::InvertIcmpCond(*cond, x_arg, y_arg),
)
}
_ => return,
}
}
@@ -590,19 +568,6 @@ fn branch_order(pos: &mut FuncCursor, cfg: &mut ControlFlowGraph, block: Block,
.replace(cond_inst)
.brnz(cond_arg, term_dest, &term_args);
}
BranchOrderKind::InvertIcmpCond(cond, x_arg, y_arg) => {
pos.func
.dfg
.replace(term_inst)
.jump(cond_dest, &cond_args[2..]);
pos.func.dfg.replace(cond_inst).br_icmp(
cond.inverse(),
x_arg,
y_arg,
term_dest,
&term_args,
);
}
}
cfg.recompute_block(pos.func, block);