a0b96902e4
This'll still go via slices eventually for large arrays, but this way slice comparisons to short arrays can use the same memcmp-avoidance tricks. Added some tests for all the combinations to make sure I didn't accidentally infinitely-recurse something.
44 lines
1.6 KiB
Rust
44 lines
1.6 KiB
Rust
// compile-flags: -C opt-level=3
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#![crate_type = "lib"]
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// #71602 reported a simple array comparison just generating a loop.
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// This was originally fixed by ensuring it generates a single bcmp,
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// but we now generate it as a load+icmp instead. `is_zero_slice` was
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// tweaked to still test the case of comparison against a slice,
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// and `is_zero_array` tests the new array-specific behaviour.
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// The optimization was then extended to short slice-to-array comparisons,
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// so the first test here now has a long slice to still get the bcmp.
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// CHECK-LABEL: @is_zero_slice_long
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#[no_mangle]
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pub fn is_zero_slice_long(data: &[u8; 456]) -> bool {
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// CHECK: :
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// CHECK-NEXT: %{{.+}} = getelementptr {{.+}}
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// CHECK-NEXT: %[[BCMP:.+]] = tail call i32 @{{bcmp|memcmp}}({{.+}})
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// CHECK-NEXT: %[[EQ:.+]] = icmp eq i32 %[[BCMP]], 0
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// CHECK-NEXT: ret i1 %[[EQ]]
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&data[..] == [0; 456]
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}
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// CHECK-LABEL: @is_zero_slice_short
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#[no_mangle]
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pub fn is_zero_slice_short(data: &[u8; 4]) -> bool {
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// CHECK: :
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// CHECK-NEXT: %[[PTR:.+]] = bitcast [4 x i8]* {{.+}} to i32*
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// CHECK-NEXT: %[[LOAD:.+]] = load i32, i32* %[[PTR]], align 1
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// CHECK-NEXT: %[[EQ:.+]] = icmp eq i32 %[[LOAD]], 0
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// CHECK-NEXT: ret i1 %[[EQ]]
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&data[..] == [0; 4]
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}
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// CHECK-LABEL: @is_zero_array
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#[no_mangle]
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pub fn is_zero_array(data: &[u8; 4]) -> bool {
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// CHECK: start:
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// CHECK-NEXT: %[[PTR:.+]] = bitcast [4 x i8]* {{.+}} to i32*
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// CHECK-NEXT: %[[LOAD:.+]] = load i32, i32* %[[PTR]], align 1
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// CHECK-NEXT: %[[EQ:.+]] = icmp eq i32 %[[LOAD]], 0
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// CHECK-NEXT: ret i1 %[[EQ]]
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*data == [0; 4]
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}
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