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Cranelift: Correctly wrap shifts in constant propagation (#5695)

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Fixes #5690
Fixes #5696

Co-authored-by: Jamey Sharp <jsharp@fastly.com>
This commit is contained in:
Nick Fitzgerald
2023-02-02 16:12:57 -08:00
committed by GitHub
parent fd67ccf9cd
commit 72c8513411
10 changed files with 176 additions and 35 deletions
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51
cranelift/codegen/src/isle_prelude.rs
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@@ -81,27 +81,42 @@ macro_rules! isle_common_prelude_methods {
}
#[inline]
fn u64_shl(&mut self, x: u64, y: u64) -> u64 {
x << y
fn imm64_shl(&mut self, ty: Type, x: Imm64, y: Imm64) -> Imm64 {
// Mask off any excess shift bits.
let shift_mask = (ty.bits() - 1) as u64;
let y = (y.bits() as u64) & shift_mask;
// Mask the result to `ty` bits.
let ty_mask = self.ty_mask(ty) as i64;
Imm64::new((x.bits() << y) & ty_mask)
}
#[inline]
fn imm64_ushr(&mut self, ty: Type, x: Imm64, y: Imm64) -> Imm64 {
let shift = u32::checked_sub(64, ty.bits()).unwrap_or(0);
let mask = u64::MAX >> shift;
let x = (x.bits() as u64) & mask;
let y = (y.bits() as u64) & mask;
let ty_mask = self.ty_mask(ty);
let x = (x.bits() as u64) & ty_mask;
// Mask off any excess shift bits.
let shift_mask = (ty.bits() - 1) as u64;
let y = (y.bits() as u64) & shift_mask;
// NB: No need to mask off high bits because they are already zero.
Imm64::new((x >> y) as i64)
}
#[inline]
fn imm64_sshr(&mut self, ty: Type, x: Imm64, y: Imm64) -> Imm64 {
// Sign extend `x` from `ty.bits()`-width to the full 64 bits.
let shift = u32::checked_sub(64, ty.bits()).unwrap_or(0);
let mask = u64::MAX >> shift;
let x = (x.bits() as u64) & mask;
let y = (y.bits() as u64) & mask;
let sext = |v| ((v << shift) as i64) >> shift;
Imm64::new(sext(x) >> sext(y))
let x = (x.bits() << shift) >> shift;
// Mask off any excess shift bits.
let shift_mask = (ty.bits() - 1) as i64;
let y = y.bits() & shift_mask;
// Mask off sign bits that aren't part of `ty`.
let ty_mask = self.ty_mask(ty) as i64;
Imm64::new((x >> y) & ty_mask)
}
#[inline]
@@ -179,14 +194,12 @@ macro_rules! isle_common_prelude_methods {
#[inline]
fn ty_mask(&mut self, ty: Type) -> u64 {
match ty.bits() {
1 => 1,
8 => 0xff,
16 => 0xffff,
32 => 0xffff_ffff,
64 => 0xffff_ffff_ffff_ffff,
_ => unimplemented!(),
}
let ty_bits = ty.bits();
debug_assert_ne!(ty_bits, 0);
let shift = 64_u64
.checked_sub(ty_bits.into())
.expect("unimplemented for > 64 bits");
u64::MAX >> shift
}
fn fits_in_16(&mut self, ty: Type) -> Option<Type> {