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Deal properly with undefined bits #1554

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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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79 changes: 38 additions & 41 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 @@ -1803,7 +1803,7 @@ impl<'a> Assemble<'a> {
match bit_size {
0 => unreachable!(),
32 => dynasm!(self.asm; cmp Rd(lhs_reg.code()), rhs),
1..=64 => {
8 | 16 | 64 => {
if pred.signed() {
self.sign_extend_to_reg64(lhs_reg, u8::try_from(bit_size).unwrap());
} else {
Expand All @@ -1819,7 +1819,7 @@ impl<'a> Assemble<'a> {
match bit_size {
0 => unreachable!(),
32 => dynasm!(self.asm; cmp Rd(lhs_reg.code()), Rd(rhs_reg.code())),
1..=64 => {
8 | 16 | 64 => {
if pred.signed() {
self.sign_extend_to_reg64(lhs_reg, u8::try_from(bit_size).unwrap());
self.sign_extend_to_reg64(rhs_reg, u8::try_from(bit_size).unwrap());
Expand All @@ -1829,7 +1829,7 @@ impl<'a> Assemble<'a> {
}
dynasm!(self.asm; cmp Rq(lhs_reg.code()), Rq(rhs_reg.code()));
}
_ => todo!(),
_ => todo!("{bit_size}"),
}
}

Expand Down 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 @@ -2580,15 +2588,15 @@ impl<'a> Assemble<'a> {
fn cg_guard(&mut self, iidx: jit_ir::InstIdx, inst: &jit_ir::GuardInst) {
let fail_label = self.guard_to_deopt(inst);
let cond = inst.cond(self.m);
// ICmp instructions evaluate to a one-byte zero/one value.
debug_assert_eq!(cond.byte_size(self.m), 1);
let [reg] = self
.ra
.assign_gp_regs(&mut self.asm, iidx, [RegConstraint::Input(cond)]);
dynasm!(self.asm
; cmp Rb(reg.code()), inst.expect() as i8 // `as` intentional.
; jne =>fail_label
);
dynasm!(self.asm ; bt Rq(reg.code()), 0);
if inst.expect() {
dynasm!(self.asm ; jnb =>fail_label);
} else {
dynasm!(self.asm ; jb =>fail_label);
}
}
}

Expand Down Expand Up @@ -4000,40 +4008,29 @@ mod tests {
entry:
%0: i16 = param 0
%1: i32 = param 1
%2: i63 = param 2
header_start [%0, %1, %2]
%4: i1 = eq %0, %0
%5: i1 = eq %1, %1
%6: i1 = eq %2, %2
header_start [%0, %1]
%3: i1 = eq %0, %0
%4: i1 = eq %1, %1
black_box %3
black_box %4
black_box %5
black_box %6
header_end [%0, %1, %2]
header_end [%0, %1]
",
"
...
; %4: i1 = eq %0, %0
; %3: i1 = eq %0, %0
......
......
movzx r.64.a, r.16.a
movzx r.64.b, r.16.b
cmp r.64.a, r.64.b
setz r.8._
...
; %5: i1 = eq %1, %1
; %4: i1 = eq %1, %1
......
......
cmp r.32.c, r.32.d
setz r.8._
; %6: i1 = eq %2, %2
......
......
shl r.64.e, 0x01
shr r.64.e, 0x01
shl r.64.f, 0x01
shr r.64.f, 0x01
cmp r.64.e, r.64.f
setz r.8._
; black_box %3
...
",
false,
Expand Down Expand Up @@ -4136,8 +4133,8 @@ mod tests {
...
; guard true, %0, [] ; ...
movzx r.64._, byte ptr ...
cmp r.8.b, 0x01
jnz 0x...
bt r.64._, 0x00
jnb 0x...
...
; deopt id for guard 0
push rsi
Expand Down Expand Up @@ -4166,8 +4163,8 @@ mod tests {
...
; guard false, %0, [] ; ...
movzx r.64._, byte ptr ...
cmp r.8.b, 0x00
jnz 0x...
bt r.64._, 0x00
jb 0x...
...
; deopt id for guard 0
push rsi
Expand Down Expand Up @@ -4199,8 +4196,8 @@ mod tests {
...
; guard false, %0, [0:%0_0: %0, 0:%0_1: 10i8, 0:%0_2: 32i8, 0:%0_3: 42i8] ; trace_gidx 0 safepoint_id 0
movzx r.64._, byte ptr ...
cmp r.8.b, 0x00
jnz 0x...
bt r.64._, 0x00
jb 0x...
...
; deopt id for guard 0
push rsi
Expand Down Expand Up @@ -4280,8 +4277,8 @@ mod tests {
cmp r.64.x, 0x03
setz bl
; guard true, %1, [] ; ...
cmp bl, 0x01
jnz 0x...
bt r.64._, 0x00
jnb 0x...
; %3: i8 = sext %1
shl rbx, 0x3f
sar rbx, 0x3f
Expand Down Expand Up @@ -4433,7 +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 @@ -4442,8 +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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