zig

commit fb4a5ccdeeddf56a0849b4168fe7a9525f36b107 (tree)
parent e4fd9acc2a7682d0d64d6d42e2882967cf3877aa
Author: Veikka Tuominen <git@vexu.eu>
Date:   Wed, 30 Nov 2022 19:31:01 +0200

llvm: make debuggers actually usable

`@llvm.dbg.value` is absolutely useless, adding a temporary alloca
to store the constant in will make it actually show up in debuggers.
The effect on performance should be minimal since there is only one
store and it the change is not applied to ReleaseSafe builds.

```zig
fn foo(a: u32, b: []const u8, c: bool, d: enum { yes, no }) void {
    _ = a; _ = b; _ = c; _ = d;
}
```
before:
```
Breakpoint 1, a.foo (a=<optimized out>, b=..., c=<optimized out>, d=<optimized out>) at a.zig:18
18          _ = d;
```
after:
```
Breakpoint 1, a.foo (a=1, b=..., c=false, d=yes) at a.zig:15
15          _ = a; _ = b; _ = c; _ = d;
(gdb) p b
$1 = {ptr = 0x20854f <a.main.anon_3888> "bar", len = 3}
```

Diffstat:
M
src/codegen/llvm.zig
 | 
12
++++++++++++

1 file changed, 12 insertions(+), 0 deletions(-)
diff --git a/src/codegen/llvm.zig b/src/codegen/llvm.zig
@@ -6088,6 +6088,12 @@ pub const FuncGen = struct {
         const insert_block = self.builder.getInsertBlock();
         if (isByRef(operand_ty)) {
             _ = dib.insertDeclareAtEnd(operand, di_local_var, debug_loc, insert_block);
+        } else if (self.dg.module.comp.bin_file.options.optimize_mode == .Debug) {
+            const alignment = operand_ty.abiAlignment(self.dg.module.getTarget());
+            const alloca = self.buildAlloca(operand.typeOf(), alignment);
+            const store_inst = self.builder.buildStore(operand, alloca);
+            store_inst.setAlignment(alignment);
+            _ = dib.insertDeclareAtEnd(alloca, di_local_var, debug_loc, insert_block);
         } else {
             _ = dib.insertDbgValueIntrinsicAtEnd(operand, di_local_var, debug_loc, insert_block);
         }
@@ -8026,6 +8032,12 @@ pub const FuncGen = struct {
             const insert_block = self.builder.getInsertBlock();
             if (isByRef(inst_ty)) {
                 _ = dib.insertDeclareAtEnd(arg_val, di_local_var, debug_loc, insert_block);
+            } else if (self.dg.module.comp.bin_file.options.optimize_mode == .Debug) {
+                const alignment = inst_ty.abiAlignment(self.dg.module.getTarget());
+                const alloca = self.buildAlloca(arg_val.typeOf(), alignment);
+                const store_inst = self.builder.buildStore(arg_val, alloca);
+                store_inst.setAlignment(alignment);
+                _ = dib.insertDeclareAtEnd(alloca, di_local_var, debug_loc, insert_block);
             } else {
                 _ = dib.insertDbgValueIntrinsicAtEnd(arg_val, di_local_var, debug_loc, insert_block);
             }