Let backends access span information

Sometimes, a backend may need to emit warnings, errors, or otherwise
need to know the span of the current item in a basic block. So, add a
set_span method to give the backend that information.

compiler/rustc_codegen_llvm/src/builder.rs

@@ -16,7 +16,7 @@ use rustc_data_structures::small_c_str::SmallCStr;
 use rustc_hir::def_id::DefId;
 use rustc_middle::ty::layout::TyAndLayout;
 use rustc_middle::ty::{self, Ty, TyCtxt};
-use rustc_span::sym;
+use rustc_span::{sym, Span};
 use rustc_target::abi::{self, Align, Size};
 use rustc_target::spec::{HasTargetSpec, Target};
 use std::borrow::Cow;
@@ -139,6 +139,8 @@ impl BuilderMethods<'a, 'tcx> for Builder<'a, 'll, 'tcx> {
         unsafe { llvm::LLVMGetInsertBlock(self.llbuilder) }
     }
 
+    fn set_span(&self, _span: Span) {}
+
     fn position_at_end(&mut self, llbb: &'ll BasicBlock) {
         unsafe {
             llvm::LLVMPositionBuilderAtEnd(self.llbuilder, llbb);

compiler/rustc_codegen_ssa/src/mir/debuginfo.rs

@@ -55,6 +55,7 @@ impl<D> DebugScope<D> {
 impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
     pub fn set_debug_loc(&self, bx: &mut Bx, source_info: mir::SourceInfo) {
         let (scope, span) = self.debug_loc(source_info);
+        bx.set_span(span);
         if let Some(scope) = scope {
             bx.set_source_location(scope, span);
         }

compiler/rustc_codegen_ssa/src/traits/builder.rs

@@ -15,6 +15,7 @@ use crate::MemFlags;
 
 use rustc_middle::ty::layout::{HasParamEnv, TyAndLayout};
 use rustc_middle::ty::Ty;
+use rustc_span::Span;
 use rustc_target::abi::{Abi, Align, Scalar, Size};
 use rustc_target::spec::HasTargetSpec;
 
@@ -44,6 +45,7 @@ pub trait BuilderMethods<'a, 'tcx>:
     fn build_sibling_block(&self, name: &str) -> Self;
     fn cx(&self) -> &Self::CodegenCx;
     fn llbb(&self) -> Self::BasicBlock;
+    fn set_span(&self, span: Span);
 
     fn position_at_end(&mut self, llbb: Self::BasicBlock);
     fn ret_void(&mut self);