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trans: Optimize initialization using repeat expressions

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This elides initialization for zero-sized arrays:
* for zero-sized elements we previously emitted an empty loop
* for arrays with a length of zero we previously emitted a loop with zero
  iterations

This emits llvm.memset() instead of a loop over each element when:
* all elements are zero integers
* elements are byte sized
This commit is contained in:
Florian Zeitz 2017-07-26 16:27:25 +02:00
parent d721c1f9e3
commit ac43d58d3a
3 changed files with 113 additions and 4 deletions
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74
src/test/codegen/slice-init.rs Normal file
View file

@ -0,0 +1,74 @@
// Copyright 2017 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.
// compile-flags: -C no-prepopulate-passes
#![crate_type = "lib"]
// CHECK-LABEL: @zero_sized_elem
#[no_mangle]
pub fn zero_sized_elem() {
// CHECK-NOT: br label %slice_loop_header{{.*}}
// CHECK-NOT: call void @llvm.memset.p0i8
let x = [(); 4];
drop(&x);
}
// CHECK-LABEL: @zero_len_array
#[no_mangle]
pub fn zero_len_array() {
// CHECK-NOT: br label %slice_loop_header{{.*}}
// CHECK-NOT: call void @llvm.memset.p0i8
let x = [4; 0];
drop(&x);
}
// CHECK-LABEL: @byte_array
#[no_mangle]
pub fn byte_array() {
// CHECK: call void @llvm.memset.p0i8.i{{[0-9]+}}(i8* {{.*}}, i8 7, i64 4
// CHECK-NOT: br label %slice_loop_header{{.*}}
let x = [7u8; 4];
drop(&x);
}
#[allow(dead_code)]
#[derive(Copy, Clone)]
enum Init {
Loop,
Memset,
}
// CHECK-LABEL: @byte_enum_array
#[no_mangle]
pub fn byte_enum_array() {
// CHECK: call void @llvm.memset.p0i8.i{{[0-9]+}}(i8* {{.*}}, i8 {{.*}}, i64 4
// CHECK-NOT: br label %slice_loop_header{{.*}}
let x = [Init::Memset; 4];
drop(&x);
}
// CHECK-LABEL: @zeroed_integer_array
#[no_mangle]
pub fn zeroed_integer_array() {
// CHECK: call void @llvm.memset.p0i8.i{{[0-9]+}}(i8* {{.*}}, i8 0, i64 16
// CHECK-NOT: br label %slice_loop_header{{.*}}
let x = [0u32; 4];
drop(&x);
}
// CHECK-LABEL: @nonzero_integer_array
#[no_mangle]
pub fn nonzero_integer_array() {
// CHECK: br label %slice_loop_header{{.*}}
// CHECK-NOT: call void @llvm.memset.p0i8
let x = [0x1a_2b_3c_4d_u32; 4];
drop(&x);
}