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Deal properly with undefined bits #1554

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merged 2 commits into from
Jan 20, 2025
Merged

Deal properly with undefined bits #1554

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30a7d45
Test comparisons using `bt`.
ltratt Jan 20, 2025
add873d
`Select` must have an `i1` conditional in LLVM IR.
ltratt Jan 20, 2025
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18 changes: 13 additions & 5 deletions ykrt/src/compile/jitc_yk/codegen/x64/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -2492,8 +2492,16 @@ impl<'a> Assemble<'a> {
RegConstraint::Input(inst.falseval(self.m)),
],
);
dynasm!(self.asm ; cmp Rb(cond_reg.code()), 0);
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I agree that this one is comparing undefined bits too!

dynasm!(self.asm ; cmove Rq(true_reg.code()), Rq(false_reg.code()));
debug_assert_eq!(
self.m
.type_(inst.cond(self.m).tyidx(self.m))
.bit_size()
.unwrap(),
1
);

dynasm!(self.asm ; bt Rq(cond_reg.code()), 0);
dynasm!(self.asm ; cmovnc Rq(true_reg.code()), Rq(false_reg.code()));
}

fn guard_to_deopt(&mut self, inst: &jit_ir::GuardInst) -> DynamicLabel {
Expand Down Expand Up @@ -4422,7 +4430,7 @@ mod tests {
codegen_and_test(
"
entry:
%0: i32 = param 0
%0: i1 = param 0
%1: i32 = %0 ? 1i32 : 2i32
black_box %1
",
Expand All @@ -4431,8 +4439,8 @@ mod tests {
; %1: i32 = %0 ? 1i32 : 2i32
mov r.64.x, 0x01
mov r.64.y, 0x02
cmp r.8.z, 0x00
cmovz r.64.x, r.64.y
bt r.64.z, 0x00
cmovnb r.64.x, r.64.y
...
",
false,
Expand Down
41 changes: 41 additions & 0 deletions ykrt/src/compile/jitc_yk/jit_ir/well_formed.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -154,6 +154,23 @@ impl Module {
);
}
}
Inst::Select(x) => {
let Ty::Integer(bitsize) = self.type_(x.cond(self).tyidx(self)) else {
panic!();
};
if *bitsize != 1 {
panic!(
"Instruction at position {iidx} trying to select on a non-i1\n {}",
self.inst(iidx).display(self, iidx)
);
}
if x.trueval(self).tyidx(self) != x.falseval(self).tyidx(self) {
panic!(
"Instruction at position {iidx} has incompatible true/false types\n {}",
self.inst(iidx).display(self, iidx)
);
}
}
Inst::SExt(x) => {
let Ty::Integer(val_bitsize) = self.type_(x.val(self).tyidx(self)) else {
panic!();
Expand Down Expand Up @@ -395,6 +412,30 @@ mod tests {
);
}

#[test]
#[should_panic(expected = "Instruction at position 1 trying to select on a non-i1")]
fn select_bad_width() {
Module::from_str(
"
entry:
%0: i32 = param 0
%1: i32 = %0 ? 1i32 : 2i32
",
);
}

#[test]
#[should_panic(expected = "Instruction at position 1 has incompatible true/false types")]
fn select_incompatible_types() {
Module::from_str(
"
entry:
%0: i1 = param 0
%1: i32 = %0 ? 1i16 : 2i32
",
);
}

#[test]
#[should_panic(
expected = "Instruction at position 1 trying to sign extend from an equal-or-larger-than integer type"
Expand Down
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