Rollup merge of rust-lang#123439 - Zalathar:constants, r=oli-obk

coverage: Remove useless constants

After rust-lang#122972 and rust-lang#123419, these constants don't serve any useful purpose, so get rid of them.

`@rustbot` label +A-code-coverage

Author: matthiaskrgr

Diff for: compiler/rustc_codegen_llvm/src/coverageinfo/mod.rs

@@ -24,8 +24,6 @@ pub(crate) mod ffi;
 pub(crate) mod map_data;
 pub mod mapgen;
 
-const VAR_ALIGN: Align = Align::EIGHT;
-
 /// A context object for maintaining all state needed by the coverageinfo module.
 pub struct CrateCoverageContext<'ll, 'tcx> {
     /// Coverage data for each instrumented function identified by DefId.
@@ -226,7 +224,8 @@ pub(crate) fn save_cov_data_to_mod<'ll, 'tcx>(
     llvm::set_global_constant(llglobal, true);
     llvm::set_linkage(llglobal, llvm::Linkage::PrivateLinkage);
     llvm::set_section(llglobal, &covmap_section_name);
-    llvm::set_alignment(llglobal, VAR_ALIGN);
+    // LLVM's coverage mapping format specifies 8-byte alignment for items in this section.
+    llvm::set_alignment(llglobal, Align::EIGHT);
     cx.add_used_global(llglobal);
 }
 
@@ -256,7 +255,8 @@ pub(crate) fn save_func_record_to_mod<'ll, 'tcx>(
     llvm::set_linkage(llglobal, llvm::Linkage::LinkOnceODRLinkage);
     llvm::set_visibility(llglobal, llvm::Visibility::Hidden);
     llvm::set_section(llglobal, covfun_section_name);
-    llvm::set_alignment(llglobal, VAR_ALIGN);
+    // LLVM's coverage mapping format specifies 8-byte alignment for items in this section.
+    llvm::set_alignment(llglobal, Align::EIGHT);
     llvm::set_comdat(cx.llmod, llglobal, &func_record_var_name);
     cx.add_used_global(llglobal);
 }

Diff for: compiler/rustc_middle/src/mir/coverage.rs

@@ -33,10 +33,6 @@ rustc_index::newtype_index! {
     pub struct CounterId {}
 }
 
-impl CounterId {
-    pub const START: Self = Self::ZERO;
-}
-
 rustc_index::newtype_index! {
     /// ID of a coverage-counter expression. Values ascend from 0.
     ///
@@ -55,10 +51,6 @@ rustc_index::newtype_index! {
     pub struct ExpressionId {}
 }
 
-impl ExpressionId {
-    pub const START: Self = Self::ZERO;
-}
-
 /// Enum that can hold a constant zero value, the ID of an physical coverage
 /// counter, or the ID of a coverage-counter expression.
 ///

Diff for: compiler/rustc_mir_transform/src/coverage/query.rs

@@ -59,7 +59,7 @@ fn coverage_ids_info<'tcx>(
             _ => None,
         })
         .max()
-        .unwrap_or(CounterId::START);
+        .unwrap_or(CounterId::ZERO);
 
     CoverageIdsInfo { max_counter_id }
 }