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Lower to a memset(undef) when Rvalue::Repeat repeats uninit

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This commit is contained in:
Ben Kimock 2025-03-17 21:29:07 -04:00
parent 43a2e9d2c7
commit 8e7d8ddffe
3 changed files with 66 additions and 4 deletions
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21
compiler/rustc_codegen_ssa/src/mir/rvalue.rs
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@ -86,13 +86,30 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
}
mir::Rvalue::Repeat(ref elem, count) => {
let cg_elem = self.codegen_operand(bx, elem);
// Do not generate the loop for zero-sized elements or empty arrays.
if dest.layout.is_zst() {
return;
}
// When the element is a const with all bytes uninit, emit a single memset that
// writes undef to the entire destination.
if let mir::Operand::Constant(const_op) = elem {
let val = self.eval_mir_constant(const_op);
if val.all_bytes_uninit(self.cx.tcx()) {
let size = bx.const_usize(dest.layout.size.bytes());
bx.memset(
dest.val.llval,
bx.const_undef(bx.type_i8()),
size,
dest.val.align,
MemFlags::empty(),
);
return;
}
}
let cg_elem = self.codegen_operand(bx, elem);
let try_init_all_same = |bx: &mut Bx, v| {
let start = dest.val.llval;
let size = bx.const_usize(dest.layout.size.bytes());