Rollup merge of #132395 - Zalathar:coverage-cx-ice, r=jieyouxu

coverage: Avoid ICE when `coverage_cx` is unexpectedly unavailable

In #132124, `coverage_cx()` was changed to panic if the context was unavailable, under the assumption that it would always be available whenever coverage instrumentation is enabled.

However, there have been reports of this change causing ICEs in `polars` CI.

I don't yet understand why this is happening, but for now it seems wisest to revert that part of the change, restoring the two early returns that had been replaced with panics.

3 files changed, 12 insertions, 2 deletions

diff --git a/compiler/rustc_codegen_llvm/src/context.rs b/compiler/rustc_codegen_llvm/src/context.rs
index 9778ff4918c..313957dda96 100644
--- a/compiler/rustc_codegen_llvm/src/context.rs
+++ b/compiler/rustc_codegen_llvm/src/context.rs
@@ -554,6 +554,7 @@ impl<'ll, 'tcx> CodegenCx<'ll, 'tcx> {
 
     /// Extra state that is only available when coverage instrumentation is enabled.
     #[inline]
+    #[track_caller]
     pub(crate) fn coverage_cx(&self) -> &coverageinfo::CrateCoverageContext<'ll, 'tcx> {
         self.coverage_cx.as_ref().expect("only called when coverage instrumentation is enabled")
     }
diff --git a/compiler/rustc_codegen_llvm/src/coverageinfo/mapgen.rs b/compiler/rustc_codegen_llvm/src/coverageinfo/mapgen.rs
index 8edd788ee36..f6378199fe2 100644
--- a/compiler/rustc_codegen_llvm/src/coverageinfo/mapgen.rs
+++ b/compiler/rustc_codegen_llvm/src/coverageinfo/mapgen.rs
@@ -54,7 +54,11 @@ pub(crate) fn finalize(cx: &CodegenCx<'_, '_>) {
         add_unused_functions(cx);
     }
 
-    let function_coverage_map = cx.coverage_cx().take_function_coverage_map();
+    // FIXME(#132395): Can this be none even when coverage is enabled?
+    let function_coverage_map = match cx.coverage_cx {
+        Some(ref cx) => cx.take_function_coverage_map(),
+        None => return,
+    };
     if function_coverage_map.is_empty() {
         // This module has no functions with coverage instrumentation
         return;
diff --git a/compiler/rustc_codegen_llvm/src/coverageinfo/mod.rs b/compiler/rustc_codegen_llvm/src/coverageinfo/mod.rs
index a298ed86276..e4ff50816b9 100644
--- a/compiler/rustc_codegen_llvm/src/coverageinfo/mod.rs
+++ b/compiler/rustc_codegen_llvm/src/coverageinfo/mod.rs
@@ -152,7 +152,12 @@ impl<'tcx> CoverageInfoBuilderMethods<'tcx> for Builder<'_, '_, 'tcx> {
             return;
         };
 
-        let mut coverage_map = bx.coverage_cx().function_coverage_map.borrow_mut();
+        // FIXME(#132395): Unwrapping `coverage_cx` here has led to ICEs in the
+        // wild, so keep this early-return until we understand why.
+        let mut coverage_map = match bx.coverage_cx {
+            Some(ref cx) => cx.function_coverage_map.borrow_mut(),
+            None => return,
+        };
         let func_coverage = coverage_map
             .entry(instance)
             .or_insert_with(|| FunctionCoverageCollector::new(instance, function_coverage_info));