From 8dddd1ae603756ef4957320880115ecc65d706a5 Mon Sep 17 00:00:00 2001
From: Zalathar <Zalathar@users.noreply.github.com>
Date: Thu, 31 Oct 2024 21:12:15 +1100
Subject: [PATCH] coverage: Avoid ICE when `coverage_cx` is unexpectedly
 unavailable

---
 compiler/rustc_codegen_llvm/src/context.rs             | 1 +
 compiler/rustc_codegen_llvm/src/coverageinfo/mapgen.rs | 6 +++++-
 compiler/rustc_codegen_llvm/src/coverageinfo/mod.rs    | 7 ++++++-
 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 9778ff4918c0d..313957dda9642 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 8edd788ee36ca..f6378199fe26e 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 a298ed86276f9..e4ff50816b97c 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));