From 5125ce83d4d402243bd1f3c7ff2bcbfff6a9e9d5 Mon Sep 17 00:00:00 2001
From: corley <28909106+corleypc@users.noreply.github.com>
Date: Sun, 11 Oct 2026 13:46:55 +0300
Subject: [PATCH] fixes packed field zeroing alignment

---
 src/llvm_backend_utility.cpp          |  5 ++++-
 tests/internal/test_packed_field.odin | 25 +++++++++++++++++++++++++
 2 files changed, 29 insertions(+), 1 deletion(-)

diff --git a/src/llvm_backend_utility.cpp b/src/llvm_backend_utility.cpp
index d6408d0ba..58108a341 100644
--- a/src/llvm_backend_utility.cpp
+++ b/src/llvm_backend_utility.cpp
@@ -173,7 +173,10 @@ gb_internal void lb_mem_zero_ptr(lbProcedure *p, LLVMValueRef ptr, Type *type, u
 		}
 		break;
 	default:
-		LLVMBuildStore(p->builder, LLVMConstNull(lb_type(p->module, type)), ptr);
+		{
+			LLVMValueRef store = LLVMBuildStore(p->builder, LLVMConstNull(lb_type(p->module, type)), ptr);
+			lb_lower_store_alignment_to_known(p, store, ptr);
+		}
 		break;
 	}
 }
diff --git a/tests/internal/test_packed_field.odin b/tests/internal/test_packed_field.odin
index 9551a75e6..fb195ed7f 100644
--- a/tests/internal/test_packed_field.odin
+++ b/tests/internal/test_packed_field.odin
@@ -294,3 +294,28 @@ test_packed_field_array_conv :: proc(t: ^testing.T) {
 	w := #force_no_inline mul_matrix(&m, &p5)
 	testing.expect(t, w == [4]f32{3, 5, 7, 9}) // exact float
 }
+
+
+// zero stores to a #packed field
+
+@(export)
+p6: Packed_Small
+
+@(private="file")
+zero_v :: proc(p: ^Packed_Small) {
+	p.v = {}
+}
+
+@(test)
+test_packed_field_zero_store :: proc(t: ^testing.T) {
+	p6.v = {1, 2, 3, 4}
+	p6.n = -1
+	p6.v = {} // folded const GEP
+	p6.n = 0
+	testing.expect(t, simd.to_array(p6.v) == [4]f32{})
+	testing.expect(t, p6.n == 0)
+
+	p6.v = {5, 6, 7, 8}
+	#force_no_inline zero_v(&p6) // GEP with packed metadata
+	testing.expect(t, simd.to_array(p6.v) == [4]f32{})
+}