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Switch ifcmp+brif folding to be icmp+brz folding, which is what frontends actually produce.

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This commit is contained in:
Tyler McMullen
2019-01-02 20:01:52 -08:00
committed by Benjamin Bouvier
parent 67cc5aafec
commit 571b87414f
2 changed files with 56 additions and 20 deletions
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25
cranelift/codegen/src/simple_preopt.rs
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@@ -556,9 +556,8 @@ enum BranchOptKind {
fn branch_opt(pos: &mut FuncCursor, inst: Inst) {
let info = match pos.func.dfg[inst] {
InstructionData::BranchInt {
opcode: Opcode::Brif,
cond: br_cond,
InstructionData::Branch {
opcode,
destination,
ref args,
} => {
@@ -566,6 +565,7 @@ fn branch_opt(pos: &mut FuncCursor, inst: Inst) {
let args = pos.func.dfg.inst_args(inst);
args[0]
};
let iconst_inst =
if let ValueDef::Result(iconst_inst, _) = pos.func.dfg.value_def(first_arg) {
iconst_inst
@@ -573,10 +573,11 @@ fn branch_opt(pos: &mut FuncCursor, inst: Inst) {
return;
};
if let InstructionData::BinaryImm {
opcode: Opcode::IfcmpImm,
imm: cmp_imm,
if let InstructionData::IntCompareImm {
opcode: Opcode::IcmpImm,
arg: cmp_arg,
cond: cmp_cond,
imm: cmp_imm,
} = pos.func.dfg[iconst_inst]
{
let cmp_imm: i64 = cmp_imm.into();
@@ -584,9 +585,17 @@ fn branch_opt(pos: &mut FuncCursor, inst: Inst) {
return;
}
let kind = match br_cond {
IntCC::NotEqual => BranchOptKind::NotEqualZero,
// icmp_imm returns non-zero when the comparison is true. So, if
// we're branching on zero, we need to invert the condition.
let cond = match opcode {
Opcode::Brz => cmp_cond.inverse(),
Opcode::Brnz => cmp_cond,
_ => return,
};
let kind = match cond {
IntCC::Equal => BranchOptKind::EqualZero,
IntCC::NotEqual => BranchOptKind::NotEqualZero,
_ => return,
};