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Sema: avoid ptr_add/ptr_sub instructions void elem type

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This commit is contained in:
Andrew Kelley 2025-09-08 18:44:50 -07:00
parent aacff8c800
commit c0bbddb007
2 changed files with 23 additions and 13 deletions
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30
src/Air.zig
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@ -166,19 +166,25 @@ pub const Inst = struct {
mod,
/// Same as `mod` with optimized float mode.
mod_optimized,
/// Add an offset to a pointer, returning a new pointer.
/// The offset is in element type units, not bytes.
/// Wrapping is illegal behavior.
/// The lhs is the pointer, rhs is the offset. Result type is the same as lhs.
/// The pointer may be a slice.
/// Uses the `ty_pl` field. Payload is `Bin`.
/// Add an offset, in element type units, to a pointer, returning a new
/// pointer. Element type may not be zero bits.
///
/// Wrapping is illegal behavior. If the newly computed address is
/// outside the provenance of the operand, the result is undefined.
///
/// Uses the `ty_pl` field. Payload is `Bin`. The lhs is the pointer,
/// rhs is the offset. Result type is the same as lhs. The operand may
/// be a slice.
ptr_add,
/// Subtract an offset from a pointer, returning a new pointer.
/// The offset is in element type units, not bytes.
/// Wrapping is illegal behavior.
/// The lhs is the pointer, rhs is the offset. Result type is the same as lhs.
/// The pointer may be a slice.
/// Uses the `ty_pl` field. Payload is `Bin`.
/// Subtract an offset, in element type units, from a pointer,
/// returning a new pointer. Element type may not be zero bits.
///
/// Wrapping is illegal behavior. If the newly computed address is
/// outside the provenance of the operand, the result is undefined.
///
/// Uses the `ty_pl` field. Payload is `Bin`. The lhs is the pointer,
/// rhs is the offset. Result type is the same as lhs. The operand may
/// be a slice.
ptr_sub,
/// Given two operands which can be floats, integers, or vectors, returns the
/// greater of the operands. For vectors it operates element-wise.

6
src/Sema.zig
View File

@ -16002,7 +16002,6 @@ fn splat(sema: *Sema, ty: Type, val: Value) !Value {
fn analyzeArithmetic(
sema: *Sema,
block: *Block,
/// TODO performance investigation: make this comptime?
zir_tag: Zir.Inst.Tag,
lhs: Air.Inst.Ref,
rhs: Air.Inst.Ref,
@ -16201,6 +16200,11 @@ fn analyzePtrArithmetic(
const ptr_info = ptr_ty.ptrInfo(zcu);
assert(ptr_info.flags.size == .many or ptr_info.flags.size == .c);
if ((try sema.typeHasOnePossibleValue(.fromInterned(ptr_info.child))) != null) {
// Offset will be multiplied by zero, so result is the same as the base pointer.
return ptr;
}
const new_ptr_ty = t: {
// Calculate the new pointer alignment.
// This code is duplicated in `Type.elemPtrType`.