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machinst x64: fix checked div sequence

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- it should mark as clobbering (def) rdx, not modifying it
- the signed-div check requires a temporary to compare against int64_min
This commit is contained in:
Benjamin Bouvier
2020-07-06 18:45:07 +02:00
parent f932bccaf8
commit d9310e8d90
4 changed files with 38 additions and 7 deletions
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21
cranelift/codegen/src/isa/x64/inst/mod.rs
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@@ -69,16 +69,20 @@ pub enum Inst {
MulHi { size: u8, signed: bool, rhs: RegMem },
/// A synthetic sequence to implement the right inline checks for remainder and division,
/// assuming the dividend is in $rax.
/// Puts the result back into $rax if is_div, $rdx if !is_div, to mimic what the div
/// assuming the dividend is in %rax.
/// Puts the result back into %rax if is_div, %rdx if !is_div, to mimic what the div
/// instruction does.
/// The generated code sequence is described in the emit's function match arm for this
/// instruction.
///
/// Note: %rdx is marked as modified by this instruction, to avoid an early clobber problem
/// with the temporary and divisor. Make sure to zero %rdx right before this instruction!
CheckedDivOrRemSeq {
is_div: bool,
is_signed: bool,
size: u8,
divisor: Reg,
tmp: Option<Writable<Reg>>,
loc: SourceLoc,
},
@@ -846,10 +850,16 @@ fn x64_get_regs(inst: &Inst, collector: &mut RegUsageCollector) {
collector.add_def(Writable::from_reg(regs::rdx()));
rhs.get_regs_as_uses(collector);
}
Inst::CheckedDivOrRemSeq { divisor, .. } => {
Inst::CheckedDivOrRemSeq { divisor, tmp, .. } => {
// Mark both fixed registers as mods, to avoid an early clobber problem in codegen
// (i.e. the temporary is allocated one of the fixed registers). This requires writing
// the rdx register *before* the instruction, which is not too bad.
collector.add_mod(Writable::from_reg(regs::rax()));
collector.add_mod(Writable::from_reg(regs::rdx()));
collector.add_use(*divisor);
if let Some(tmp) = tmp {
collector.add_def(*tmp);
}
}
Inst::SignExtendRaxRdx { .. } => {
collector.add_use(regs::rax());
@@ -1038,8 +1048,11 @@ fn x64_map_regs<RUM: RegUsageMapper>(inst: &mut Inst, mapper: &RUM) {
}
Inst::Div { divisor, .. } => divisor.map_uses(mapper),
Inst::MulHi { rhs, .. } => rhs.map_uses(mapper),
Inst::CheckedDivOrRemSeq { divisor, .. } => {
Inst::CheckedDivOrRemSeq { divisor, tmp, .. } => {
map_use(mapper, divisor);
if let Some(tmp) = tmp {
map_def(mapper, tmp)
}
}
Inst::SignExtendRaxRdx { .. } => {}
Inst::XMM_Mov_RM_R {