Auto merge of #28428 - dotdash:same_adjust, r=nikomatsakis
Currently, we're generating adjustments, for example, to get from &[u8] to &[u8], which is unneeded and kicks us out of trans_into() into trans() which means an additional stack slot and copy in the unoptimized code.
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commit
2be0d0ad92
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@ -110,6 +110,10 @@ impl<'f, 'tcx> Coerce<'f, 'tcx> {
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a,
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b);
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if a == b {
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return Ok(None);
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}
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// Consider coercing the subtype to a DST
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let unsize = self.unpack_actual_value(a, |a| {
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self.coerce_unsized(a, b)
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@ -0,0 +1,28 @@
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// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
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// file at the top-level directory of this distribution and at
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// http://rust-lang.org/COPYRIGHT.
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//
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// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
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// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
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// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
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// option. This file may not be copied, modified, or distributed
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// except according to those terms.
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// compile-flags: -C no-prepopulate-passes
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// Hack to get the correct size for the length part in slices
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// CHECK: @helper([[USIZE:i[0-9]+]])
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#[no_mangle]
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fn helper(_: usize) {
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}
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// CHECK-LABEL: @no_op_slice_adjustment
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#[no_mangle]
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pub fn no_op_slice_adjustment(x: &[u8]) -> &[u8] {
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// We used to generate an extra alloca and memcpy for the block's trailing expression value, so
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// check that we copy directly to the return value slot
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// CHECK: [[SRC:%[0-9]+]] = bitcast { i8*, [[USIZE]] }* %x to
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// CHECK: [[DST:%[0-9]+]] = bitcast { i8*, [[USIZE]] }* %sret_slot to i8*
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// CHECK: call void @llvm.memcpy.{{.*}}(i8* [[DST]], i8* [[SRC]],
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{ x }
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}
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