Rollup merge of #136640 - Zalathar:debuginfo-align-bits, r=compiler-errors

Debuginfo for function ZSTs should have alignment of 8 bits, not 1 bit

In #116096, function ZSTs were made to have debuginfo that gives them an alignment of “1”. But because alignment in LLVM debuginfo is denoted in *bits*, not bytes, this resulted in an alignment specification of 1 bit instead of 1 byte.

I don't know whether this has any practical consequences, but I noticed that a test started failing when I accidentally fixed the mistake while working on #136632, so I extracted the fix (and the test adjustment) to this PR.

compiler/rustc_codegen_llvm/src/debuginfo/metadata.rs

@@ -319,19 +319,16 @@ fn build_subroutine_type_di_node<'ll, 'tcx>(
     // This is actually a function pointer, so wrap it in pointer DI.
     let name = compute_debuginfo_type_name(cx.tcx, fn_ty, false);
     let (size, align) = match fn_ty.kind() {
-        ty::FnDef(..) => (0, 1),
-        ty::FnPtr(..) => (
-            cx.tcx.data_layout.pointer_size.bits(),
-            cx.tcx.data_layout.pointer_align.abi.bits() as u32,
-        ),
+        ty::FnDef(..) => (Size::ZERO, Align::ONE),
+        ty::FnPtr(..) => (cx.tcx.data_layout.pointer_size, cx.tcx.data_layout.pointer_align.abi),
         _ => unreachable!(),
     };
     let di_node = unsafe {
         llvm::LLVMRustDIBuilderCreatePointerType(
             DIB(cx),
             fn_di_node,
-            size,
-            align,
+            size.bits(),
+            align.bits() as u32,
             0, // Ignore DWARF address space.
             name.as_c_char_ptr(),
             name.len(),

compiler/rustc_codegen_llvm/src/debuginfo/mod.rs

@@ -633,7 +633,7 @@ impl<'ll, 'tcx> DebugInfoCodegenMethods<'tcx> for CodegenCx<'ll, 'tcx> {
                 true,
                 DIFlags::FlagZero,
                 argument_index,
-                align.bytes() as u32,
+                align.bits() as u32,
             )
         }
     }