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Remove fallthrough instruction

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This commit is contained in:
bjorn3
2021-10-12 14:22:07 +02:00
parent 5b24e117ee
commit 1fd491dadd
9 changed files with 30 additions and 86 deletions
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20
cranelift/codegen/meta/src/shared/instructions.rs
View File

@@ -38,26 +38,6 @@ fn define_control_flow(
.is_branch(true),
);
ig.push(
Inst::new(
"fallthrough",
r#"
Fall through to the next block.
This is the same as `jump`, except the destination block must be
the next one in the layout.
Jumps are turned into fall-through instructions by the branch
relaxation pass. There is no reason to use this instruction outside
that pass.
"#,
&formats.jump,
)
.operands_in(vec![block, args])
.is_terminator(true)
.is_branch(true),
);
let Testable = &TypeVar::new(
"Testable",
"A scalar boolean or integer type",

6
cranelift/codegen/src/ir/function.rs
View File

@@ -274,12 +274,12 @@ impl Function {
let mut inst_iter = inst_iter.skip_while(|&inst| !dfg[inst].opcode().is_branch());
// A conditional branch is permitted in a basic block only when followed
// by a terminal jump or fallthrough instruction.
// by a terminal jump instruction.
if let Some(_branch) = inst_iter.next() {
if let Some(next) = inst_iter.next() {
match dfg[next].opcode() {
Opcode::Fallthrough | Opcode::Jump => (),
_ => return Err((next, "post-branch instruction not fallthrough or jump")),
Opcode::Jump => (),
_ => return Err((next, "post-branch instruction not jump")),
}
}
}

19
cranelift/codegen/src/isa/aarch64/lower_inst.rs
View File

@@ -2158,19 +2158,7 @@ pub(crate) fn lower_insn_to_regs<C: LowerCtx<I = Inst>>(
ctx.emit(Inst::gen_move(writable_xreg(PINNED_REG), rm, I64));
}
Opcode::Spill
| Opcode::Fill
| Opcode::FillNop
| Opcode::CopyNop
| Opcode::AdjustSpDown
| Opcode::AdjustSpUpImm
| Opcode::AdjustSpDownImm
| Opcode::IfcmpSp => {
panic!("Unused opcode should not be encountered.");
}
Opcode::Jump
| Opcode::Fallthrough
| Opcode::Brz
| Opcode::Brnz
| Opcode::BrIcmp
@@ -3789,7 +3777,7 @@ pub(crate) fn lower_branch<C: LowerCtx<I = Inst>>(
let op0 = ctx.data(branches[0]).opcode();
let op1 = ctx.data(branches[1]).opcode();
assert!(op1 == Opcode::Jump || op1 == Opcode::Fallthrough);
assert!(op1 == Opcode::Jump);
let taken = BranchTarget::Label(targets[0]);
// not_taken target is the target of the second branch, even if it is a Fallthrough
// instruction: because we reorder blocks while we lower, the fallthrough in the new
@@ -3932,11 +3920,8 @@ pub(crate) fn lower_branch<C: LowerCtx<I = Inst>>(
// Must be an unconditional branch or an indirect branch.
let op = ctx.data(branches[0]).opcode();
match op {
Opcode::Jump | Opcode::Fallthrough => {
Opcode::Jump => {
assert!(branches.len() == 1);
// In the Fallthrough case, the machine-independent driver
// fills in `targets[0]` with our fallthrough block, so this
// is valid for both Jump and Fallthrough.
ctx.emit(Inst::Jump {
dest: BranchTarget::Label(targets[0]),
});

14
cranelift/codegen/src/isa/arm32/lower_inst.rs
View File

@@ -542,10 +542,9 @@ pub(crate) fn lower_branch<C: LowerCtx<I = Inst>>(
) -> CodegenResult<()> {
// A block should end with at most two branches. The first may be a
// conditional branch; a conditional branch can be followed only by an
// unconditional branch or fallthrough. Otherwise, if only one branch,
// it may be an unconditional branch, a fallthrough, a return, or a
// trap. These conditions are verified by `is_ebb_basic()` during the
// verifier pass.
// unconditional branch. Otherwise, if only one branch, it may be an
// unconditional branch, a return, or a trap. These conditions are verified
// by `is_ebb_basic()` during the verifier pass.
assert!(branches.len() <= 2);
if branches.len() == 2 {
@@ -553,7 +552,7 @@ pub(crate) fn lower_branch<C: LowerCtx<I = Inst>>(
let op0 = ctx.data(branches[0]).opcode();
let op1 = ctx.data(branches[1]).opcode();
assert!(op1 == Opcode::Jump || op1 == Opcode::Fallthrough);
assert!(op1 == Opcode::Jump);
let taken = BranchTarget::Label(targets[0]);
let not_taken = BranchTarget::Label(targets[1]);
@@ -586,11 +585,8 @@ pub(crate) fn lower_branch<C: LowerCtx<I = Inst>>(
// Must be an unconditional branch or an indirect branch.
let op = ctx.data(branches[0]).opcode();
match op {
Opcode::Jump | Opcode::Fallthrough => {
Opcode::Jump => {
assert_eq!(branches.len(), 1);
// In the Fallthrough case, the machine-independent driver
// fills in `targets[0]` with our fallthrough block, so this
// is valid for both Jump and Fallthrough.
ctx.emit(Inst::Jump {
dest: BranchTarget::Label(targets[0]),
});

8
cranelift/codegen/src/isa/s390x/lower.rs
View File

@@ -2909,7 +2909,6 @@ fn lower_insn_to_regs<C: LowerCtx<I = Inst>>(
}
Opcode::Jump
| Opcode::Fallthrough
| Opcode::Brz
| Opcode::Brnz
| Opcode::BrIcmp
@@ -2980,7 +2979,7 @@ fn lower_branch<C: LowerCtx<I = Inst>>(
let op0 = ctx.data(branches[0]).opcode();
let op1 = ctx.data(branches[1]).opcode();
assert!(op1 == Opcode::Jump || op1 == Opcode::Fallthrough);
assert!(op1 == Opcode::Jump);
let taken = BranchTarget::Label(targets[0]);
let not_taken = BranchTarget::Label(targets[1]);
@@ -3029,11 +3028,8 @@ fn lower_branch<C: LowerCtx<I = Inst>>(
// Must be an unconditional branch or an indirect branch.
let op = ctx.data(branches[0]).opcode();
match op {
Opcode::Jump | Opcode::Fallthrough => {
Opcode::Jump => {
assert!(branches.len() == 1);
// In the Fallthrough case, the machine-independent driver
// fills in `targets[0]` with our fallthrough block, so this
// is valid for both Jump and Fallthrough.
ctx.emit(Inst::Jump {
dest: BranchTarget::Label(targets[0]),
});

10
cranelift/codegen/src/isa/x64/lower.rs
View File

@@ -6879,7 +6879,6 @@ fn lower_insn_to_regs<C: LowerCtx<I = Inst>>(
}
Opcode::Jump
| Opcode::Fallthrough
| Opcode::Brz
| Opcode::Brnz
| Opcode::BrIcmp
@@ -6931,13 +6930,10 @@ impl LowerBackend for X64Backend {
op0,
op1
);
assert!(op1 == Opcode::Jump || op1 == Opcode::Fallthrough);
assert!(op1 == Opcode::Jump);
let taken = targets[0];
// not_taken target is the target of the second branch, even if it is a Fallthrough
// instruction: because we reorder blocks while we lower, the fallthrough in the new
// order is not (necessarily) the same as the fallthrough in CLIF. So we use the
// explicitly-provided target.
// not_taken target is the target of the second branch.
let not_taken = targets[1];
match op0 {
@@ -7147,7 +7143,7 @@ impl LowerBackend for X64Backend {
// Must be an unconditional branch or trap.
let op = ctx.data(branches[0]).opcode();
match op {
Opcode::Jump | Opcode::Fallthrough => {
Opcode::Jump => {
ctx.emit(Inst::jmp_known(targets[0]));
}

13
cranelift/codegen/src/machinst/lower.rs
View File

@@ -1295,20 +1295,12 @@ impl<'func, I: VCodeInst> LowerCtx for Lower<'func, I> {
pub(crate) fn visit_block_succs<F: FnMut(Inst, Block)>(f: &Function, block: Block, mut visit: F) {
for inst in f.layout.block_likely_branches(block) {
if f.dfg[inst].opcode().is_branch() {
visit_branch_targets(f, block, inst, &mut visit);
visit_branch_targets(f, inst, &mut visit);
}
}
}
fn visit_branch_targets<F: FnMut(Inst, Block)>(
f: &Function,
block: Block,
inst: Inst,
visit: &mut F,
) {
if f.dfg[inst].opcode() == Opcode::Fallthrough {
visit(inst, f.layout.next_block(block).unwrap());
} else {
fn visit_branch_targets<F: FnMut(Inst, Block)>(f: &Function, inst: Inst, visit: &mut F) {
match f.dfg[inst].analyze_branch(&f.dfg.value_lists) {
BranchInfo::NotABranch => {}
BranchInfo::SingleDest(dest, _) => {
@@ -1324,4 +1316,3 @@ fn visit_branch_targets<F: FnMut(Inst, Block)>(
}
}
}
}

6
cranelift/filetests/filetests/runtests/fibonacci.clif
View File

@@ -6,12 +6,12 @@ block0(v0: i32):
v1 = icmp_imm ule v0, 2
v2 = iconst.i32 1
brnz v1, block3(v2) ; handle base case, n <= 2
fallthrough block1(v0, v2)
jump block1(v0, v2)
block1(v4: i32, v5:i32):
v6 = iconst.i32 1
v7 = iadd_imm v4, -2
fallthrough block2(v7, v5, v6)
jump block2(v7, v5, v6)
block2(v10: i32, v11: i32, v12: i32): ; params: n, fib(n-1), fib(n-2)
v13 = iadd v11, v12
@@ -40,7 +40,7 @@ function %fibonacci_recursive(i32) -> i32 {
block0(v0: i32):
v1 = icmp_imm ule v0, 2
brnz v1, block2
fallthrough block1(v0)
jump block1(v0)
block1(v10: i32):
v11 = iadd_imm v10, -1

2
cranelift/interpreter/src/step.rs
View File

@@ -221,7 +221,7 @@ where
// Interpret a Cranelift instruction.
Ok(match inst.opcode() {
Opcode::Jump | Opcode::Fallthrough => ControlFlow::ContinueAt(branch(), args()?),
Opcode::Jump => ControlFlow::ContinueAt(branch(), args()?),
Opcode::Brz => branch_when(
!arg(0)?
.convert(ValueConversionKind::ToBoolean)?