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correct comment on branchless version

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Brendan Hansknecht 2024-07-22 17:50:44 -07:00
parent 52af8c588e
commit 8b58161c73
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1 changed files with 2 additions and 3 deletions
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5
crates/compiler/builtins/bitcode/src/sort.zig
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@ -99,7 +99,7 @@ inline fn parity_merge_two(ptr: [*]u8, swap: [*]u8, cmp_data: Opaque, cmp: Compa
inline fn head_branchless_merge(dest: *[*]u8, left: *[*]u8, right: *[*]u8, cmp_data: Opaque, cmp: CompareFn, element_width: usize, copy: CopyFn) void {
// Note there is a much simpler version here:
// *ptd++ = cmp(ptl, ptr) <= 0 ? *ptl++ : *ptr++;
// That said, it is only used with gcc, so I assume it has optimization issues with llvm.
// That said, not sure how to write that in zig and guarantee it is branchless.
// Thus using the longer form.
const lte = @as(utils.Ordering, @enumFromInt(cmp(cmp_data, left.*, right.*))) != utils.Ordering.GT;
// TODO: double check this is branchless.
@ -119,8 +119,7 @@ inline fn head_branchless_merge(dest: *[*]u8, left: *[*]u8, right: *[*]u8, cmp_d
inline fn tail_branchless_merge(dest: *[*]u8, left: *[*]u8, right: *[*]u8, cmp_data: Opaque, cmp: CompareFn, element_width: usize, copy: CopyFn) void {
// Note there is a much simpler version here:
// *tpd-- = cmp(tpl, tpr) > 0 ? *tpl-- : *tpr--;
// That said, it is only used with gcc, so I assume it has optimization issues with llvm.
// Thus using the longer form.
// That said, not sure how to write that in zig and guarantee it is branchless.
const lte = @as(utils.Ordering, @enumFromInt(cmp(cmp_data, left.*, right.*))) != utils.Ordering.GT;
// TODO: double check this is branchless.
const y = if (lte) element_width else 0;