stage2: introduce store_safe AIR instruction

store:
The value to store may be undefined, in which case the destination
memory region has undefined bytes after this instruction is
evaluated. In such case ignoring this instruction is legal
lowering.

store_safe:
Same as `store`, except if the value to store is undefined, the
memory region should be filled with 0xaa bytes, and any other
safety metadata such as Valgrind integrations should be notified of
this memory region being undefined.

1 files changed, 8 insertions, 2 deletions

diff --git a/src/arch/x86_64/CodeGen.zig b/src/arch/x86_64/CodeGen.zig
index 316322c60b..c857e65ec9 100644
--- a/src/arch/x86_64/CodeGen.zig
+++ b/src/arch/x86_64/CodeGen.zig
@@ -1035,7 +1035,8 @@ fn genBody(self: *Self, body: []const Air.Inst.Index) InnerError!void {
             .ptrtoint        => try self.airPtrToInt(inst),
             .ret             => try self.airRet(inst),
             .ret_load        => try self.airRetLoad(inst),
-            .store           => try self.airStore(inst),
+            .store           => try self.airStore(inst, false),
+            .store_safe      => try self.airStore(inst, true),
             .struct_field_ptr=> try self.airStructFieldPtr(inst),
             .struct_field_val=> try self.airStructFieldVal(inst),
             .array_to_slice  => try self.airArrayToSlice(inst),
@@ -3936,7 +3937,12 @@ fn store(self: *Self, ptr: MCValue, value: MCValue, ptr_ty: Type, value_ty: Type
     }
 }
 
-fn airStore(self: *Self, inst: Air.Inst.Index) !void {
+fn airStore(self: *Self, inst: Air.Inst.Index, safety: bool) !void {
+    if (safety) {
+        // TODO if the value is undef, write 0xaa bytes to dest
+    } else {
+        // TODO if the value is undef, don't lower this instruction
+    }
     const bin_op = self.air.instructions.items(.data)[inst].bin_op;
     const ptr = try self.resolveInst(bin_op.lhs);
     const ptr_ty = self.air.typeOf(bin_op.lhs);