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

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

In rust-lang#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 rust-lang#136632, so I extracted the fix (and the test adjustment) to this PR.

Author: matthiaskrgr

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,
             )
         }
     }

tests/codegen/debug-fndef-size.rs

@@ -1,4 +1,6 @@
-// Verify that `i32::cmp` FnDef type is declared with size 0 and align 1 in LLVM debuginfo.
+// Verify that `i32::cmp` FnDef type is declared with a size of 0 and an
+// alignment of 8 bits (1 byte) in LLVM debuginfo.
+
 //@ compile-flags: -O -g -Cno-prepopulate-passes
 //@ ignore-msvc the types are mangled differently
 
@@ -14,5 +16,5 @@ pub fn main() {
 
 // CHECK: %compare.dbg.spill = alloca [0 x i8], align 1
 // CHECK: dbg{{.}}declare({{(metadata )?}}ptr %compare.dbg.spill, {{(metadata )?}}![[VAR:.*]], {{(metadata )?}}!DIExpression()
-// CHECK: ![[TYPE:.*]] = !DIDerivedType(tag: DW_TAG_pointer_type, name: "fn(&i32, &i32) -> core::cmp::Ordering", baseType: !{{.*}}, align: 1, dwarfAddressSpace: {{.*}})
-// CHECK: ![[VAR]] = !DILocalVariable(name: "compare", scope: !{{.*}}, file: !{{.*}}, line: {{.*}}, type: ![[TYPE]], align: 1)
+// CHECK: ![[TYPE:.*]] = !DIDerivedType(tag: DW_TAG_pointer_type, name: "fn(&i32, &i32) -> core::cmp::Ordering", baseType: !{{.*}}, align: 8, dwarfAddressSpace: {{.*}})
+// CHECK: ![[VAR]] = !DILocalVariable(name: "compare", scope: !{{.*}}, file: !{{.*}}, line: {{.*}}, type: ![[TYPE]], align: 8)