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x64: handle tests of b1 values correctly (only LSB is defined).

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Previously, `select` and `brz`/`brnz` instructions, when given a `b1`
boolean argument, would test whether that boolean argument was nonzero,
rather than whether its LSB was nonzero. Since our invariant for mapping
CLIF state to machine state is that bits beyond the width of a value are
undefined, the proper lowering is to test only the LSB.

(aarch64 does not have the same issue because its `Extend` pseudoinst
already properly handles masking of b1 values when a zero-extend is
requested, as it is for select/brz/brnz.)

Found by Nathan Ringo on Zulip [1] (thanks!).

[1]
https://bytecodealliance.zulipchat.com/#narrow/stream/217117-cranelift/topic/bnot.20on.20b1s
This commit is contained in:
Chris Fallin
2021-01-04 16:42:24 -08:00
parent 2b325a1878
commit dbd2241b60
7 changed files with 271 additions and 29 deletions
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52
cranelift/codegen/src/isa/x64/inst/mod.rs
View File

@@ -168,9 +168,10 @@ pub enum Inst {
dst: Writable<Reg>,
},
/// Integer comparisons/tests: cmp (b w l q) (reg addr imm) reg.
/// Integer comparisons/tests: cmp or test (b w l q) (reg addr imm) reg.
CmpRmiR {
size: u8, // 1, 2, 4 or 8
opcode: CmpOpcode,
src: RegMemImm,
dst: Reg,
},
@@ -913,8 +914,30 @@ impl Inst {
) -> Inst {
src.assert_regclass_is(RegClass::I64);
debug_assert!(size == 8 || size == 4 || size == 2 || size == 1);
debug_assert!(dst.get_class() == RegClass::I64);
Inst::CmpRmiR { size, src, dst }
debug_assert_eq!(dst.get_class(), RegClass::I64);
Inst::CmpRmiR {
size,
src,
dst,
opcode: CmpOpcode::Cmp,
}
}
/// Does a comparison of dst & src for operands of size `size`.
pub(crate) fn test_rmi_r(
size: u8, // 1, 2, 4 or 8
src: RegMemImm,
dst: Reg,
) -> Inst {
src.assert_regclass_is(RegClass::I64);
debug_assert!(size == 8 || size == 4 || size == 2 || size == 1);
debug_assert_eq!(dst.get_class(), RegClass::I64);
Inst::CmpRmiR {
size,
src,
dst,
opcode: CmpOpcode::Test,
}
}
pub(crate) fn trap(trap_code: TrapCode) -> Inst {
@@ -1597,12 +1620,23 @@ impl PrettyPrint for Inst {
dst.to_reg().show_rru(mb_rru)
),
Inst::CmpRmiR { size, src, dst } => format!(
"{} {}, {}",
ljustify2("cmp".to_string(), suffix_bwlq(*size)),
src.show_rru_sized(mb_rru, *size),
show_ireg_sized(*dst, mb_rru, *size)
),
Inst::CmpRmiR {
size,
src,
dst,
opcode,
} => {
let op = match opcode {
CmpOpcode::Cmp => "cmp",
CmpOpcode::Test => "test",
};
format!(
"{} {}, {}",
ljustify2(op.to_string(), suffix_bwlq(*size)),
src.show_rru_sized(mb_rru, *size),
show_ireg_sized(*dst, mb_rru, *size)
)
}
Inst::Setcc { cc, dst } => format!(
"{} {}",