From 1d280b012d52fa95ed59942701e1a32c662e58a3 Mon Sep 17 00:00:00 2001
From: Nikita Popov <nikita.ppv@gmail.com>
Date: Sat, 20 Feb 2021 16:43:05 +0100
Subject: [PATCH] Don't directly expose coverage::CounterMappingRegion via FFI

The definition of this struct changes in LLVM 12 due to the addition
of branch coverage support. To avoid future mismatches, declare our
own struct and then convert between them.
---
 .../src/coverageinfo/mod.rs                   |  4 ++--
 compiler/rustc_codegen_llvm/src/llvm/ffi.rs   |  6 ++---
 .../llvm-wrapper/CoverageMappingWrapper.cpp   | 24 +++++++++++++++++--
 3 files changed, 26 insertions(+), 8 deletions(-)

diff --git a/compiler/rustc_codegen_llvm/src/coverageinfo/mod.rs b/compiler/rustc_codegen_llvm/src/coverageinfo/mod.rs
index e777f363eb08..e47b8fde40fe 100644
--- a/compiler/rustc_codegen_llvm/src/coverageinfo/mod.rs
+++ b/compiler/rustc_codegen_llvm/src/coverageinfo/mod.rs
@@ -162,7 +162,7 @@ pub(crate) fn write_filenames_section_to_buffer<'a>(
 pub(crate) fn write_mapping_to_buffer(
     virtual_file_mapping: Vec<u32>,
     expressions: Vec<CounterExpression>,
-    mut mapping_regions: Vec<CounterMappingRegion>,
+    mapping_regions: Vec<CounterMappingRegion>,
     buffer: &RustString,
 ) {
     unsafe {
@@ -171,7 +171,7 @@ pub(crate) fn write_mapping_to_buffer(
             virtual_file_mapping.len() as c_uint,
             expressions.as_ptr(),
             expressions.len() as c_uint,
-            mapping_regions.as_mut_ptr(),
+            mapping_regions.as_ptr(),
             mapping_regions.len() as c_uint,
             buffer,
         );
diff --git a/compiler/rustc_codegen_llvm/src/llvm/ffi.rs b/compiler/rustc_codegen_llvm/src/llvm/ffi.rs
index 9eac7ad17b04..7f7575e58c9e 100644
--- a/compiler/rustc_codegen_llvm/src/llvm/ffi.rs
+++ b/compiler/rustc_codegen_llvm/src/llvm/ffi.rs
@@ -676,9 +676,7 @@ pub mod coverageinfo {
     /// array", encoded separately), and source location (start and end positions of the represented
     /// code region).
     ///
-    /// Aligns with [llvm::coverage::CounterMappingRegion](https://github.com/rust-lang/llvm-project/blob/rustc/11.0-2020-10-12/llvm/include/llvm/ProfileData/Coverage/CoverageMapping.h#L224-L227)
-    /// Important: The Rust struct layout (order and types of fields) must match its C++
-    /// counterpart.
+    /// Matches LLVMRustCounterMappingRegion.
     #[derive(Copy, Clone, Debug)]
     #[repr(C)]
     pub struct CounterMappingRegion {
@@ -1796,7 +1794,7 @@ extern "C" {
         NumVirtualFileMappingIDs: c_uint,
         Expressions: *const coverage_map::CounterExpression,
         NumExpressions: c_uint,
-        MappingRegions: *mut coverageinfo::CounterMappingRegion,
+        MappingRegions: *const coverageinfo::CounterMappingRegion,
         NumMappingRegions: c_uint,
         BufferOut: &RustString,
     );
diff --git a/compiler/rustc_llvm/llvm-wrapper/CoverageMappingWrapper.cpp b/compiler/rustc_llvm/llvm-wrapper/CoverageMappingWrapper.cpp
index 25badc3f4e17..e97d96e3a4ea 100644
--- a/compiler/rustc_llvm/llvm-wrapper/CoverageMappingWrapper.cpp
+++ b/compiler/rustc_llvm/llvm-wrapper/CoverageMappingWrapper.cpp
@@ -8,6 +8,17 @@
 
 using namespace llvm;
 
+struct LLVMRustCounterMappingRegion {
+  coverage::Counter Count;
+  uint32_t FileID;
+  uint32_t ExpandedFileID;
+  uint32_t LineStart;
+  uint32_t ColumnStart;
+  uint32_t LineEnd;
+  uint32_t ColumnEnd;
+  coverage::CounterMappingRegion::RegionKind Kind;
+};
+
 extern "C" void LLVMRustCoverageWriteFilenamesSectionToBuffer(
     const char* const Filenames[],
     size_t FilenamesLen,
@@ -27,13 +38,22 @@ extern "C" void LLVMRustCoverageWriteMappingToBuffer(
     unsigned NumVirtualFileMappingIDs,
     const coverage::CounterExpression *Expressions,
     unsigned NumExpressions,
-    coverage::CounterMappingRegion *MappingRegions,
+    LLVMRustCounterMappingRegion *RustMappingRegions,
     unsigned NumMappingRegions,
     RustStringRef BufferOut) {
+  // Convert from FFI representation to LLVM representation.
+  SmallVector<coverage::CounterMappingRegion, 0> MappingRegions;
+  MappingRegions.reserve(NumMappingRegions);
+  for (const auto &Region : makeArrayRef(RustMappingRegions, NumMappingRegions)) {
+    MappingRegions.emplace_back(
+        Region.Count, Region.FileID, Region.ExpandedFileID,
+        Region.LineStart, Region.ColumnStart, Region.LineEnd, Region.ColumnEnd,
+        Region.Kind);
+  }
   auto CoverageMappingWriter = coverage::CoverageMappingWriter(
       makeArrayRef(VirtualFileMappingIDs, NumVirtualFileMappingIDs),
       makeArrayRef(Expressions, NumExpressions),
-      makeMutableArrayRef(MappingRegions, NumMappingRegions));
+      MappingRegions);
   RawRustStringOstream OS(BufferOut);
   CoverageMappingWriter.write(OS);
 }