Commit c0bbddb0071830eb9a6afd96124a24176f263b6a | zig

author	Andrew Kelley <andrew@ziglang.org> 2025-09-08 18:44:50-07:00
committer	Andrew Kelley <andrew@ziglang.org> 2025-09-20 18:33:00-07:00
log	c0bbddb0071830eb9a6afd96124a24176f263b6a
tree	8e6e0becec62a8ab058db2b6cd3f9515f16750e2
parent	aacff8c80091c0187057e65d96108f46962f98a3

Sema: avoid ptr_add/ptr_sub instructions void elem type

2 files changed, 23 insertions(+), 13 deletions(-)

src
- Air.zig
- Sema.zig

src/Air.zig+18-12

...	@@ -166,19 +166,25 @@ pub const Inst = struct {	...	@@ -166,19 +166,25 @@ pub const Inst = struct {
166	mod,	166	mod,
167	/// Same as `mod` with optimized float mode.	167	/// Same as `mod` with optimized float mode.
168	mod_optimized,	168	mod_optimized,
169	/// Add an offset to a pointer, returning a new pointer.	169	/// Add an offset, in element type units, to a pointer, returning a new
170	/// The offset is in element type units, not bytes.	170	/// pointer. Element type may not be zero bits.
171	/// Wrapping is illegal behavior.	171	///
172	/// The lhs is the pointer, rhs is the offset. Result type is the same as lhs.	172	/// Wrapping is illegal behavior. If the newly computed address is
173	/// The pointer may be a slice.	173	/// outside the provenance of the operand, the result is undefined.
174	/// Uses the `ty_pl` field. Payload is `Bin`.	174	///
		175	/// Uses the `ty_pl` field. Payload is `Bin`. The lhs is the pointer,
		176	/// rhs is the offset. Result type is the same as lhs. The operand may
		177	/// be a slice.
175	ptr_add,	178	ptr_add,
176	/// Subtract an offset from a pointer, returning a new pointer.	179	/// Subtract an offset, in element type units, from a pointer,
177	/// The offset is in element type units, not bytes.	180	/// returning a new pointer. Element type may not be zero bits.
178	/// Wrapping is illegal behavior.	181	///
179	/// The lhs is the pointer, rhs is the offset. Result type is the same as lhs.	182	/// Wrapping is illegal behavior. If the newly computed address is
180	/// The pointer may be a slice.	183	/// outside the provenance of the operand, the result is undefined.
181	/// Uses the `ty_pl` field. Payload is `Bin`.	184	///
		185	/// Uses the `ty_pl` field. Payload is `Bin`. The lhs is the pointer,
		186	/// rhs is the offset. Result type is the same as lhs. The operand may
		187	/// be a slice.
182	ptr_sub,	188	ptr_sub,
183	/// Given two operands which can be floats, integers, or vectors, returns the	189	/// Given two operands which can be floats, integers, or vectors, returns the
184	/// greater of the operands. For vectors it operates element-wise.	190	/// greater of the operands. For vectors it operates element-wise.

src/Sema.zig+5-1

 @@ -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`.