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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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21
cranelift/codegen/src/legalizer/mod.rs
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@@ -54,27 +54,6 @@ pub fn simple_legalize(func: &mut ir::Function, cfg: &mut ControlFlowGraph, isa:
while let Some(inst) = pos.next_inst() {
match pos.func.dfg[inst] {
// control flow
InstructionData::BranchIcmp {
opcode: ir::Opcode::BrIcmp,
cond,
destination,
ref args,
} => {
let a = args.get(0, &pos.func.dfg.value_lists).unwrap();
let b = args.get(1, &pos.func.dfg.value_lists).unwrap();
let block_args = args.as_slice(&pos.func.dfg.value_lists)[2..].to_vec();
let old_block = pos.func.layout.pp_block(inst);
pos.func.dfg.clear_results(inst);
let icmp_res = pos.func.dfg.replace(inst).icmp(cond, a, b);
let mut pos = FuncCursor::new(pos.func).after_inst(inst);
pos.use_srcloc(inst);
pos.ins().brnz(icmp_res, destination, &block_args);
cfg.recompute_block(pos.func, destination);
cfg.recompute_block(pos.func, old_block);
}
InstructionData::CondTrap {
opcode:
opcode @ (ir::Opcode::Trapnz | ir::Opcode::Trapz | ir::Opcode::ResumableTrapnz),