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Simple preopt: fold instructions using simple algebraic identities;

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This commit is contained in:
Benjamin Bouvier
2019-07-10 19:50:41 +02:00
parent 2fef2eef67
commit 23ac723d4c
2 changed files with 89 additions and 46 deletions
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51
cranelift/codegen/src/simple_preopt.rs
View File

@@ -577,13 +577,17 @@ fn simplify(pos: &mut FuncCursor, inst: Inst) {
_ => {}
},
InstructionData::BinaryImm { opcode, arg, imm } => match opcode {
InstructionData::BinaryImm { opcode, arg, imm } => {
let ty = pos.func.dfg.ctrl_typevar(inst);
let mut imm = imm;
match opcode {
Opcode::IaddImm
| Opcode::ImulImm
| Opcode::BorImm
| Opcode::BandImm
| Opcode::BxorImm => {
// Fold binary_op(C2, binary_op(C1, x)) into binary_op(binary_op(C1 | C2), x)
// Fold binary_op(C2, binary_op(C1, x)) into binary_op(binary_op(C1, C2), x)
if let ValueDef::Result(arg_inst, _) = pos.func.dfg.value_def(arg) {
if let InstructionData::BinaryImm {
opcode: prev_opcode,
@@ -592,7 +596,6 @@ fn simplify(pos: &mut FuncCursor, inst: Inst) {
} = &pos.func.dfg[arg_inst]
{
if opcode == *prev_opcode {
let ty = pos.func.dfg.ctrl_typevar(inst);
if ty == pos.func.dfg.ctrl_typevar(arg_inst) {
let lhs: i64 = imm.into();
let rhs: i64 = (*prev_imm).into();
@@ -610,6 +613,7 @@ fn simplify(pos: &mut FuncCursor, inst: Inst) {
.dfg
.replace(inst)
.BinaryImm(opcode, ty, new_imm, arg);
imm = new_imm;
}
}
}
@@ -621,8 +625,47 @@ fn simplify(pos: &mut FuncCursor, inst: Inst) {
return;
}
}
_ => {}
},
};
// Replace operations that are no-ops.
match (opcode, imm.into()) {
(Opcode::IaddImm, 0)
| (Opcode::ImulImm, 1)
| (Opcode::SdivImm, 1)
| (Opcode::UdivImm, 1)
| (Opcode::BorImm, 0)
| (Opcode::BandImm, -1)
| (Opcode::BxorImm, 0)
| (Opcode::RotlImm, 0)
| (Opcode::RotrImm, 0)
| (Opcode::IshlImm, 0)
| (Opcode::UshrImm, 0)
| (Opcode::SshrImm, 0) => {
// Alias the result value with the original argument.
let results = pos.func.dfg.detach_results(inst);
debug_assert!(results.len(&pos.func.dfg.value_lists) == 1);
let first_result = results.get(0, &pos.func.dfg.value_lists).unwrap();
pos.func.dfg.change_to_alias(first_result, arg);
// Replace instruction by a nop.
pos.func.dfg.replace(inst).nop();
return;
}
(Opcode::ImulImm, 0) | (Opcode::BandImm, 0) => {
// Replace by zero.
pos.func.dfg.replace(inst).iconst(ty, 0);
return;
}
(Opcode::BorImm, -1) => {
// Replace by minus one.
pos.func.dfg.replace(inst).iconst(ty, -1);
return;
}
_ => {}
}
}
InstructionData::IntCompare { opcode, cond, args } => {
debug_assert_eq!(opcode, Opcode::Icmp);

16
cranelift/filetests/filetests/simple_preopt/div_by_const_power_of_2.clif
View File

@@ -11,11 +11,11 @@ ebb0(v0: i32):
return v1
}
; converted to a copy
; converted to a nop
function %t_udiv32_p1(i32) -> i32 {
ebb0(v0: i32):
v1 = udiv_imm v0, 1
; check: copy v0
; check: nop
return v1
}
@@ -46,11 +46,11 @@ ebb0(v0: i64):
return v1
}
; converted to a copy
; converted to a nop
function %t_udiv64_p1(i64) -> i64 {
ebb0(v0: i64):
v1 = udiv_imm v0, 1
; check: copy v0
; check: nop
return v1
}
@@ -81,11 +81,11 @@ ebb0(v0: i32):
return v1
}
; converted to a copy
; converted to a nop
function %t_sdiv32_p1(i32) -> i32 {
ebb0(v0: i32):
v1 = sdiv_imm v0, 1
; check: copy v0
; check: nop
return v1
}
@@ -192,11 +192,11 @@ ebb0(v0: i64):
return v1
}
; converted to a copy
; converted to a nop
function %t_sdiv64_p1(i64) -> i64 {
ebb0(v0: i64):
v1 = sdiv_imm v0, 1
; check: copy v0
; check: nop
return v1
}