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In cases where it is legal, we should prefer poison values over undef values. This replaces undef with poison for aggregate construction and for uninhabited types. There are more places where we can likely use poison, but I wanted to stay conservative to start with. In particular the aggregate case is important for newer LLVM versions, which are not able to handle an undef base value during early optimization due to poison-propagation concerns.
30 lines
1.1 KiB
Rust
30 lines
1.1 KiB
Rust
// compile-flags: -C no-prepopulate-passes -Copt-level=0
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#![crate_type = "lib"]
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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]+]] %_1)
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#[no_mangle]
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pub 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: %0 = insertvalue { {{\[0 x i8\]\*|ptr}}, [[USIZE]] } poison, {{\[0 x i8\]\*|ptr}} %x.0, 0
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// CHECK: %1 = insertvalue { {{\[0 x i8\]\*|ptr}}, [[USIZE]] } %0, [[USIZE]] %x.1, 1
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// CHECK: ret { {{\[0 x i8\]\*|ptr}}, [[USIZE]] } %1
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{ x }
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}
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// CHECK-LABEL: @no_op_slice_adjustment2
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#[no_mangle]
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pub fn no_op_slice_adjustment2(x: &[u8]) -> &[u8] {
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// We used to generate an extra alloca and memcpy for the function's return value, so check
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// that there's no memcpy (the slice is written to sret_slot element-wise)
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// CHECK-NOT: call void @llvm.memcpy.
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no_op_slice_adjustment(x)
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}
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