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Use llvm.memset.p0i8.* to initialize all same-bytes arrays

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This commit is contained in:
Oli Scherer 2025-01-08 16:29:32 +00:00
parent 65ea9f3eb4
commit 65b01cb182
2 changed files with 12 additions and 10 deletions
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10
compiler/rustc_codegen_ssa/src/mir/rvalue.rs
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@ -97,12 +97,16 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
let start = dest.val.llval; let start = dest.val.llval;
let size = bx.const_usize(dest.layout.size.bytes()); let size = bx.const_usize(dest.layout.size.bytes());
// Use llvm.memset.p0i8.* to initialize all zero arrays // Use llvm.memset.p0i8.* to initialize all same byte arrays
if bx.cx().const_to_opt_u128(v, false) == Some(0) { if let Some(int) = bx.cx().const_to_opt_u128(v, false) {
let fill = bx.cx().const_u8(0); let bytes = &int.to_le_bytes()[..cg_elem.layout.size.bytes_usize()];
let first = bytes[0];
if bytes[1..].iter().all(|&b| b == first) {
let fill = bx.cx().const_u8(first);
bx.memset(start, fill, size, dest.val.align, MemFlags::empty()); bx.memset(start, fill, size, dest.val.align, MemFlags::empty());
return true; return true;
} }
}
// Use llvm.memset.p0i8.* to initialize byte arrays // Use llvm.memset.p0i8.* to initialize byte arrays
let v = bx.from_immediate(v); let v = bx.from_immediate(v);

8
tests/codegen/slice-init.rs
View file

@ -65,16 +65,14 @@ pub fn nonzero_integer_array() {
const N: usize = 100; const N: usize = 100;
// FIXME: The two bytes of the u16 are the same, so we should
// just use memset, too.
// CHECK-LABEL: @u16_init_one_bytes // CHECK-LABEL: @u16_init_one_bytes
#[no_mangle] #[no_mangle]
pub fn u16_init_one_bytes() -> [u16; N] { pub fn u16_init_one_bytes() -> [u16; N] {
// CHECK-NOT: select // CHECK-NOT: select
// CHECK: br // CHECK-NOT: br
// CHECK-NOT: switch // CHECK-NOT: switch
// CHECK: icmp // CHECK-NOT: icmp
// CHECK-NOT: call void @llvm.memset.p0 // CHECK: call void @llvm.memset.p0
[const { u16::from_be_bytes([1, 1]) }; N] [const { u16::from_be_bytes([1, 1]) }; N]
} }