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https://github.com/rust-lang/rust
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4c002fce9d
This replaces the drop_in_place reference with null in vtables. On librustc_driver.so, this drops about ~17k dynamic relocations from the output, since many vtables can now be placed in read-only memory, rather than having a relocated pointer included. This makes a tradeoff by adding a null check at vtable call sites. That's hard to avoid without changing the vtable format (e.g., to use a pc-relative relocation instead of an absolute address, and avoid the dynamic relocation that way). But it seems likely that the check is cheap at runtime.
17 lines
352 B
Rust
17 lines
352 B
Rust
//@ compile-flags: -O
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#![crate_type = "lib"]
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// CHECK-LABEL: @loop_skips_vtable_load
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#[no_mangle]
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pub fn loop_skips_vtable_load(x: &dyn Fn()) {
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// CHECK: load ptr, ptr %0{{.*}}, !invariant.load
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// CHECK-NEXT: tail call void %1
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// CHECK-NOT: load ptr
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x();
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for _ in 0..100 {
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// CHECK: tail call void %1
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x();
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}
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}
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