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cranelift: Add a conditional branch instruction with two targets (#5446)

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Add a conditional branch instruction with two targets: brif. This instruction will eventually replace brz and brnz, as it encompasses the behavior of both.

This PR also changes the InstructionData layout for instruction formats that hold BlockCall values, taking the same approach we use for Value arguments. This allows branch_destination to return a slice to the BlockCall values held in the instruction, rather than requiring that we pattern match on InstructionData to fetch the then/else blocks.

Function generation for fuzzing has been updated to generate uses of brif, and I've run the cranelift-fuzzgen target locally for hours without triggering any new failures.
This commit is contained in:
Trevor Elliott
2023-01-24 14:37:16 -08:00
committed by GitHub
parent ec6922ff24
commit b58a197d33
35 changed files with 943 additions and 159 deletions
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25
cranelift/codegen/src/remove_constant_phis.rs
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@@ -4,7 +4,6 @@ use crate::dominator_tree::DominatorTree;
use crate::fx::FxHashMap;
use crate::fx::FxHashSet;
use crate::ir;
use crate::ir::instructions::BranchInfo;
use crate::ir::Function;
use crate::ir::{Block, BlockCall, Inst, Value};
use crate::timing;
@@ -112,6 +111,9 @@ impl AbstractValue {
struct OutEdge<'a> {
/// An instruction that transfers control.
inst: Inst,
/// The index into branch_destinations for this instruction that corresponds
/// to this edge.
branch_index: u32,
/// The block that control is transferred to.
block: Block,
/// The arguments to that block.
@@ -126,7 +128,13 @@ impl<'a> OutEdge<'a> {
/// Returns `None` if this is an edge without any block arguments, which
/// means we can ignore it for this analysis's purposes.
#[inline]
fn new(bump: &'a Bump, dfg: &ir::DataFlowGraph, inst: Inst, block: BlockCall) -> Option<Self> {
fn new(
bump: &'a Bump,
dfg: &ir::DataFlowGraph,
inst: Inst,
branch_index: usize,
block: BlockCall,
) -> Option<Self> {
let inst_var_args = block.args_slice(&dfg.value_lists);
// Skip edges without params.
@@ -136,6 +144,7 @@ impl<'a> OutEdge<'a> {
Some(OutEdge {
inst,
branch_index: branch_index as u32,
block: block.block(&dfg.value_lists),
args: bump.alloc_slice_fill_iter(
inst_var_args
@@ -231,12 +240,8 @@ pub fn do_remove_constant_phis(func: &mut Function, domtree: &mut DominatorTree)
let mut summary = BlockSummary::new(&bump, formals);
for inst in func.layout.block_insts(b) {
let idetails = &func.dfg.insts[inst];
// Note that multi-dest transfers (i.e., branch tables) don't
// carry parameters in our IR, so we only have to care about
// `SingleDest` here.
if let BranchInfo::SingleDest(dest) = idetails.analyze_branch() {
if let Some(edge) = OutEdge::new(&bump, &func.dfg, inst, dest) {
for (ix, dest) in func.dfg.insts[inst].branch_destination().iter().enumerate() {
if let Some(edge) = OutEdge::new(&bump, &func.dfg, inst, ix, *dest) {
summary.dests.push(edge);
}
}
@@ -378,7 +383,9 @@ pub fn do_remove_constant_phis(func: &mut Function, domtree: &mut DominatorTree)
}
let dfg = &mut func.dfg;
let block = dfg.insts[edge.inst].branch_destination_mut().unwrap();
let block =
&mut dfg.insts[edge.inst].branch_destination_mut()[edge.branch_index as usize];
old_actuals.extend(block.args_slice(&dfg.value_lists));
// Check that the numbers of arguments make sense.