llvm: store undef if safety is disabled

src/codegen/llvm.zig

@@ -8226,27 +8226,23 @@ pub const FuncGen = struct {
         // possibly do the safety 0xaa bytes for undefined.
         const val_is_undef = if (self.air.value(bin_op.rhs)) |val| val.isUndefDeep() else false;
         if (val_is_undef) {
-            {
-                // TODO let's handle this in AIR rather than by having each backend
-                // check the optimization mode of the compilation because the plan is
-                // to support setting the optimization mode at finer grained scopes
-                // which happens in Sema. Codegen should not be aware of this logic.
-                // I think this comment is basically the same as the other TODO comment just
-                // above but I'm leaving them both here to make it look super messy and
-                // thereby bait contributors (or let's be honest, probably myself) into
-                // fixing this instead of letting it rot.
-                const safety = switch (self.dg.module.comp.bin_file.options.optimize_mode) {
-                    .ReleaseSmall, .ReleaseFast => false,
-                    .Debug, .ReleaseSafe => true,
-                };
-                if (!safety) {
-                    return null;
-                }
-            }
+            // TODO let's handle this in AIR rather than by having each backend
+            // check the optimization mode of the compilation because the plan is
+            // to support setting the optimization mode at finer grained scopes
+            // which happens in Sema. Codegen should not be aware of this logic.
+            // I think this comment is basically the same as the other TODO comment just
+            // above but I'm leaving them both here to make it look super messy and
+            // thereby bait contributors (or let's be honest, probably myself) into
+            // fixing this instead of letting it rot.
+            const safety = switch (self.dg.module.comp.bin_file.options.optimize_mode) {
+                .ReleaseSmall, .ReleaseFast => false,
+                .Debug, .ReleaseSafe => true,
+            };
+
             const target = self.dg.module.getTarget();
             const operand_size = operand_ty.abiSize(target);
             const u8_llvm_ty = self.context.intType(8);
-            const fill_char = u8_llvm_ty.constInt(0xaa, .False);
+            const fill_char = if (safety) u8_llvm_ty.constInt(0xaa, .False) else u8_llvm_ty.getUndef();
             const dest_ptr_align = ptr_ty.ptrAlignment(target);
             const usize_llvm_ty = try self.dg.lowerType(Type.usize);
             const len = usize_llvm_ty.constInt(operand_size, .False);
@@ -8522,7 +8518,15 @@ pub const FuncGen = struct {
         const val_is_undef = if (self.air.value(extra.lhs)) |val| val.isUndefDeep() else false;
         const len = try self.resolveInst(extra.rhs);
         const u8_llvm_ty = self.context.intType(8);
-        const fill_char = if (val_is_undef) u8_llvm_ty.constInt(0xaa, .False) else value;
+        const fill_char = blk: {
+            if (!val_is_undef) break :blk value;
+            const safety = switch (self.dg.module.comp.bin_file.options.optimize_mode) {
+                .ReleaseSmall, .ReleaseFast => false,
+                .Debug, .ReleaseSafe => true,
+            };
+            if (safety) break :blk u8_llvm_ty.constInt(0xaa, .False);
+            break :blk u8_llvm_ty.getUndef();
+        };
         const target = self.dg.module.getTarget();
         const dest_ptr_align = ptr_ty.ptrAlignment(target);
         _ = self.builder.buildMemSet(dest_ptr, fill_char, len, dest_ptr_align, ptr_ty.isVolatilePtr());