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Migrate cranelift-wasm to brif (#5638)

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Incrementally working towards removing brz and brnz completely.
This commit is contained in:
Trevor Elliott
2023-01-27 10:34:41 -08:00
committed by GitHub
parent 915801551b
commit 058d93bc64
3 changed files with 76 additions and 42 deletions
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14
cranelift/frontend/src/frontend.rs
View File

@@ -680,14 +680,14 @@ impl<'a> FunctionBuilder<'a> {
///
/// **Note:** You are responsible for maintaining the coherence with the arguments of
/// other jump instructions.
pub fn change_jump_destination(&mut self, inst: Inst, new_dest: Block) {
pub fn change_jump_destination(&mut self, inst: Inst, old_block: Block, new_block: Block) {
let dfg = &mut self.func.dfg;
for old_dest in dfg.insts[inst].branch_destination_mut() {
self.func_ctx
.ssa
.remove_block_predecessor(old_dest.block(&dfg.value_lists), inst);
old_dest.set_block(new_dest, &mut dfg.value_lists);
self.func_ctx.ssa.declare_block_predecessor(new_dest, inst);
for block in dfg.insts[inst].branch_destination_mut() {
if block.block(&dfg.value_lists) == old_block {
self.func_ctx.ssa.remove_block_predecessor(old_block, inst);
block.set_block(new_block, &mut dfg.value_lists);
self.func_ctx.ssa.declare_block_predecessor(new_block, inst);
}
}
}

96
cranelift/wasm/src/code_translator.rs
View File

@@ -292,6 +292,7 @@ pub fn translate_operator<FE: FuncEnvironment + ?Sized>(
Operator::If { blockty } => {
let val = state.pop1();
let next_block = builder.create_block();
let (params, results) = blocktype_params_results(validator, *blockty)?;
let (destination, else_data) = if params.clone().eq(results.clone()) {
// It is possible there is no `else` block, so we will only
@@ -301,21 +302,38 @@ pub fn translate_operator<FE: FuncEnvironment + ?Sized>(
// up discovering an `else`, then we will allocate a block for it
// and go back and patch the jump.
let destination = block_with_params(builder, results.clone(), environ)?;
let branch_inst =
canonicalise_then_brz(builder, val, destination, state.peekn(params.len()));
(destination, ElseData::NoElse { branch_inst })
let branch_inst = canonicalise_brif(
builder,
val,
next_block,
&[],
destination,
state.peekn(params.len()),
);
(
destination,
ElseData::NoElse {
branch_inst,
placeholder: destination,
},
)
} else {
// The `if` type signature is not valid without an `else` block,
// so we eagerly allocate the `else` block here.
let destination = block_with_params(builder, results.clone(), environ)?;
let else_block = block_with_params(builder, params.clone(), environ)?;
canonicalise_then_brz(builder, val, else_block, state.peekn(params.len()));
canonicalise_brif(
builder,
val,
next_block,
&[],
else_block,
state.peekn(params.len()),
);
builder.seal_block(else_block);
(destination, ElseData::WithElse { else_block })
};
let next_block = builder.create_block();
canonicalise_then_jump(builder, next_block, &[]);
builder.seal_block(next_block); // Only predecessor is the current block.
builder.switch_to_block(next_block);
@@ -357,7 +375,10 @@ pub fn translate_operator<FE: FuncEnvironment + ?Sized>(
// Ensure we have a block for the `else` block (it may have
// already been pre-allocated, see `ElseData` for details).
let else_block = match *else_data {
ElseData::NoElse { branch_inst } => {
ElseData::NoElse {
branch_inst,
placeholder,
} => {
let (params, _results) =
blocktype_params_results(validator, blocktype)?;
debug_assert_eq!(params.len(), num_return_values);
@@ -370,7 +391,11 @@ pub fn translate_operator<FE: FuncEnvironment + ?Sized>(
);
state.popn(params.len());
builder.change_jump_destination(branch_inst, else_block);
builder.change_jump_destination(
branch_inst,
placeholder,
else_block,
);
builder.seal_block(else_block);
else_block
}
@@ -2171,6 +2196,7 @@ fn translate_unreachable_operator<FE: FuncEnvironment + ?Sized>(
ir::Block::reserved_value(),
ElseData::NoElse {
branch_inst: ir::Inst::reserved_value(),
placeholder: ir::Block::reserved_value(),
},
0,
0,
@@ -2198,7 +2224,10 @@ fn translate_unreachable_operator<FE: FuncEnvironment + ?Sized>(
state.reachable = true;
let else_block = match *else_data {
ElseData::NoElse { branch_inst } => {
ElseData::NoElse {
branch_inst,
placeholder,
} => {
let (params, _results) =
blocktype_params_results(validator, blocktype)?;
let else_block = block_with_params(builder, params, environ)?;
@@ -2206,7 +2235,11 @@ fn translate_unreachable_operator<FE: FuncEnvironment + ?Sized>(
frame.truncate_value_stack_to_else_params(&mut state.stack);
// We change the target of the branch instruction.
builder.change_jump_destination(branch_inst, else_block);
builder.change_jump_destination(
branch_inst,
placeholder,
else_block,
);
builder.seal_block(else_block);
else_block
}
@@ -2816,10 +2849,9 @@ fn translate_br_if(
) {
let val = state.pop1();
let (br_destination, inputs) = translate_br_if_args(relative_depth, state);
canonicalise_then_brnz(builder, val, br_destination, inputs);
let next_block = builder.create_block();
canonicalise_then_jump(builder, next_block, &[]);
canonicalise_brif(builder, val, br_destination, inputs, next_block, &[]);
builder.seal_block(next_block); // The only predecessor is the current block.
builder.switch_to_block(next_block);
}
@@ -3120,28 +3152,28 @@ fn canonicalise_then_jump(
builder.ins().jump(destination, canonicalised)
}
/// The same but for a `brz` instruction.
fn canonicalise_then_brz(
/// The same but for a `brif` instruction.
fn canonicalise_brif(
builder: &mut FunctionBuilder,
cond: ir::Value,
destination: ir::Block,
params: &[Value],
block_then: ir::Block,
params_then: &[ir::Value],
block_else: ir::Block,
params_else: &[ir::Value],
) -> ir::Inst {
let mut tmp_canonicalised = SmallVec::<[ir::Value; 16]>::new();
let canonicalised = canonicalise_v128_values(&mut tmp_canonicalised, builder, params);
builder.ins().brz(cond, destination, canonicalised)
}
/// The same but for a `brnz` instruction.
fn canonicalise_then_brnz(
builder: &mut FunctionBuilder,
cond: ir::Value,
destination: ir::Block,
params: &[Value],
) -> ir::Inst {
let mut tmp_canonicalised = SmallVec::<[ir::Value; 16]>::new();
let canonicalised = canonicalise_v128_values(&mut tmp_canonicalised, builder, params);
builder.ins().brnz(cond, destination, canonicalised)
let mut tmp_canonicalised_then = SmallVec::<[ir::Value; 16]>::new();
let canonicalised_then =
canonicalise_v128_values(&mut tmp_canonicalised_then, builder, params_then);
let mut tmp_canonicalised_else = SmallVec::<[ir::Value; 16]>::new();
let canonicalised_else =
canonicalise_v128_values(&mut tmp_canonicalised_else, builder, params_else);
builder.ins().brif(
cond,
block_then,
canonicalised_then,
block_else,
canonicalised_else,
)
}
/// A helper for popping and bitcasting a single value; since SIMD values can lose their type by

8
cranelift/wasm/src/state.rs
View File

@@ -22,6 +22,9 @@ pub enum ElseData {
/// instruction that needs to be fixed up to point to the new `else`
/// block rather than the destination block after the `if...end`.
branch_inst: Inst,
/// The placeholder block we're replacing.
placeholder: Block,
},
/// We have already allocated an `else` block.
@@ -43,9 +46,8 @@ pub enum ElseData {
/// - `num_return_values`: number of values returned by the control block;
/// - `original_stack_size`: size of the value stack at the beginning of the control block.
///
/// Moreover, the `if` frame has the `branch_inst` field that points to the `brz` instruction
/// separating the `true` and `false` branch. The `loop` frame has a `header` field that references
/// the `Block` that contains the beginning of the body of the loop.
/// The `loop` frame has a `header` field that references the `Block` that contains the beginning
/// of the body of the loop.
#[derive(Debug)]
pub enum ControlStackFrame {
If {