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codegen: writer().writeByteNTimes -> appendNTimes

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Both ways do the same thing but I think the compiler might have an
easier time optimizing `appendNTimes` because it does less
things/the path is shorter.

I have not done any benchmarking at runtime but have compared the
instruction count of both ways a little here: https://zig.godbolt.org/z/vr193W9oj
`b` (`appendNTimes`) is ~103 instructions while `a`
(`writer().writeByteNTimes`) is ~117 instructions.

And looking at the implementation of `writeByteNTimes`, it only seems to
buffer up 256 bytes before doing another `writeAll` which for
`std.ArrayList` probably means another allocation, whereas when directly
using `appendNTimes`, the entire exact additional capacity required is known from the start.

Either way, this would be more consistent anyway.
This commit is contained in:
r00ster91 2023-07-22 00:16:08 +02:00 • committed by Andrew Kelley
parent 619140c0d2
commit d962ad5ea0
1 changed files with 11 additions and 11 deletions
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22
src/codegen.zig
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@ -294,7 +294,7 @@ pub fn generateSymbol(
const padding = math.cast(usize, padded_end - unpadded_end) orelse return error.Overflow;
if (padding > 0) {
try code.writer().writeByteNTimes(0, padding);
try code.appendNTimes(0, padding);
}
}
@ -307,7 +307,7 @@ pub fn generateSymbol(
const padding = math.cast(usize, padded_end - unpadded_end) orelse return error.Overflow;
if (padding > 0) {
try code.writer().writeByteNTimes(0, padding);
try code.appendNTimes(0, padding);
}
}
},
@ -367,7 +367,7 @@ pub fn generateSymbol(
.fail => |em| return Result{ .fail = em },
}
} else {
try code.writer().writeByteNTimes(0, abi_size);
try code.appendNTimes(0, abi_size);
}
} else {
const padding = abi_size - (math.cast(usize, payload_type.abiSize(mod)) orelse return error.Overflow) - 1;
@ -382,7 +382,7 @@ pub fn generateSymbol(
}
}
try code.writer().writeByte(@intFromBool(payload_val != null));
try code.writer().writeByteNTimes(0, padding);
try code.appendNTimes(0, padding);
}
},
.aggregate => |aggregate| switch (mod.intern_pool.indexToKey(typed_value.ty.toIntern())) {
@ -433,7 +433,7 @@ pub fn generateSymbol(
error.DivisionByZero => unreachable,
else => |e| return e,
})) orelse return error.Overflow;
if (padding > 0) try code.writer().writeByteNTimes(0, padding);
if (padding > 0) try code.appendNTimes(0, padding);
},
.anon_struct_type => |tuple| {
const struct_begin = code.items.len;
@ -465,7 +465,7 @@ pub fn generateSymbol(
return error.Overflow;
if (padding > 0) {
try code.writer().writeByteNTimes(0, padding);
try code.appendNTimes(0, padding);
}
}
},
@ -540,7 +540,7 @@ pub fn generateSymbol(
const padding = math.cast(usize, padded_field_end - unpadded_field_end) orelse return error.Overflow;
if (padding > 0) {
try code.writer().writeByteNTimes(0, padding);
try code.appendNTimes(0, padding);
}
}
}
@ -573,7 +573,7 @@ pub fn generateSymbol(
assert(union_ty.haveFieldTypes());
const field_ty = union_ty.fields.values()[field_index].ty;
if (!field_ty.hasRuntimeBits(mod)) {
try code.writer().writeByteNTimes(0xaa, math.cast(usize, layout.payload_size) orelse return error.Overflow);
try code.appendNTimes(0xaa, math.cast(usize, layout.payload_size) orelse return error.Overflow);
} else {
switch (try generateSymbol(bin_file, src_loc, .{
.ty = field_ty,
@ -585,7 +585,7 @@ pub fn generateSymbol(
const padding = math.cast(usize, layout.payload_size - field_ty.abiSize(mod)) orelse return error.Overflow;
if (padding > 0) {
try code.writer().writeByteNTimes(0, padding);
try code.appendNTimes(0, padding);
}
}
@ -599,7 +599,7 @@ pub fn generateSymbol(
}
if (layout.padding > 0) {
try code.writer().writeByteNTimes(0, layout.padding);
try code.appendNTimes(0, layout.padding);
}
}
},
@ -734,7 +734,7 @@ fn lowerDeclRef(
const decl = mod.declPtr(decl_index);
const is_fn_body = decl.ty.zigTypeTag(mod) == .Fn;
if (!is_fn_body and !decl.ty.hasRuntimeBits(mod)) {
try code.writer().writeByteNTimes(0xaa, @divExact(ptr_width, 8));
try code.appendNTimes(0xaa, @divExact(ptr_width, 8));
return Result.ok;
}