stage2: add debug info for locals in the LLVM backend

Adds 2 new AIR instructions:
 * dbg_var_ptr
 * dbg_var_val

Sema no longer emits dbg_stmt AIR instructions when strip=true.

LLVM backend: fixed lowerPtrToVoid when calling ptrAlignment on
the element type is problematic.

LLVM backend: fixed alloca instructions improperly getting debug
location annotated, causing chaotic debug info behavior.

zig_llvm.cpp: fixed incorrect bindings for a function that should use
unsigned integers for line and column.

A bunch of C test cases regressed because the new dbg_var AIR
instructions caused their operands to be alive, exposing latent bugs.
Mostly it's just a problem that the C backend lowers mutable
and const slices to the same C type, so we need to represent that in the
C backend instead of printing two duplicate typedefs.

1 files changed, 14 insertions, 0 deletions

diff --git a/src/codegen/c.zig b/src/codegen/c.zig
index f1da1fdc0c..5ab84520a4 100644
--- a/src/codegen/c.zig
+++ b/src/codegen/c.zig
@@ -1721,6 +1721,10 @@ fn genBody(f: *Function, body: []const Air.Inst.Index) error{ AnalysisFail, OutO
             .union_init       => try airUnionInit(f, inst),
             .prefetch         => try airPrefetch(f, inst),
 
+            .dbg_var_ptr,
+            .dbg_var_val,
+            => try airDbgVar(f, inst),
+
             .call              => try airCall(f, inst, .auto),
             .call_always_tail  => try airCall(f, inst, .always_tail),
             .call_never_tail   => try airCall(f, inst, .never_tail),
@@ -2651,6 +2655,16 @@ fn airDbgStmt(f: *Function, inst: Air.Inst.Index) !CValue {
     return CValue.none;
 }
 
+fn airDbgVar(f: *Function, inst: Air.Inst.Index) !CValue {
+    const pl_op = f.air.instructions.items(.data)[inst].pl_op;
+    const name = f.air.nullTerminatedString(pl_op.payload);
+    const operand = try f.resolveInst(pl_op.operand);
+    _ = operand;
+    const writer = f.object.writer();
+    try writer.print("/* var:{s} */\n", .{name});
+    return CValue.none;
+}
+
 fn airBlock(f: *Function, inst: Air.Inst.Index) !CValue {
     const ty_pl = f.air.instructions.items(.data)[inst].ty_pl;
     const extra = f.air.extraData(Air.Block, ty_pl.payload);