Auto merge of #113430 - Zalathar:hash, r=b-naber

Remove `LLVMRustCoverageHashCString`

Coverage has two FFI functions for computing the hash of a byte string. One takes a ptr/len pair (`LLVMRustCoverageHashByteArray`), and the other takes a NUL-terminated C string (`LLVMRustCoverageHashCString`).

But on closer inspection, the C string version is unnecessary. The calling-side code converts a Rust `&str` into a `CString`, and the C++ code then immediately turns it back into a ptr/len string before actually hashing it. So we can just call the ptr/len version directly instead.

---

This PR also fixes a bug in the C++ declaration of `LLVMRustCoverageHashByteArray`. It should be `size_t`, since that's what is declared and passed on the Rust side, and it's what `StrRef`'s constructor expects to receive on the callee side.

compiler/rustc_codegen_llvm/src/coverageinfo/mapgen.rs

@@ -63,7 +63,7 @@ pub fn finalize(cx: &CodegenCx<'_, '_>) {
     let mut function_data = Vec::new();
     for (instance, function_coverage) in function_coverage_map {
         debug!("Generate function coverage for {}, {:?}", cx.codegen_unit.name(), instance);
-        let mangled_function_name = tcx.symbol_name(instance).to_string();
+        let mangled_function_name = tcx.symbol_name(instance).name;
         let source_hash = function_coverage.source_hash();
         let is_used = function_coverage.is_used();
         let (expressions, counter_regions) =
@@ -95,7 +95,7 @@ pub fn finalize(cx: &CodegenCx<'_, '_>) {
 
     let filenames_size = filenames_buffer.len();
     let filenames_val = cx.const_bytes(&filenames_buffer);
-    let filenames_ref = coverageinfo::hash_bytes(filenames_buffer);
+    let filenames_ref = coverageinfo::hash_bytes(&filenames_buffer);
 
     // Generate the LLVM IR representation of the coverage map and store it in a well-known global
     let cov_data_val = mapgen.generate_coverage_map(cx, version, filenames_size, filenames_val);
@@ -228,7 +228,7 @@ impl CoverageMapGenerator {
 /// specific, well-known section and name.
 fn save_function_record(
     cx: &CodegenCx<'_, '_>,
-    mangled_function_name: String,
+    mangled_function_name: &str,
     source_hash: u64,
     filenames_ref: u64,
     coverage_mapping_buffer: Vec<u8>,
@@ -238,7 +238,7 @@ fn save_function_record(
     let coverage_mapping_size = coverage_mapping_buffer.len();
     let coverage_mapping_val = cx.const_bytes(&coverage_mapping_buffer);
 
-    let func_name_hash = coverageinfo::hash_str(&mangled_function_name);
+    let func_name_hash = coverageinfo::hash_bytes(mangled_function_name.as_bytes());
     let func_name_hash_val = cx.const_u64(func_name_hash);
     let coverage_mapping_size_val = cx.const_u32(coverage_mapping_size as u32);
     let source_hash_val = cx.const_u64(source_hash);

compiler/rustc_codegen_llvm/src/coverageinfo/mod.rs

@@ -373,12 +373,7 @@ pub(crate) fn write_mapping_to_buffer(
     }
 }
 
-pub(crate) fn hash_str(strval: &str) -> u64 {
-    let strval = CString::new(strval).expect("null error converting hashable str to C string");
-    unsafe { llvm::LLVMRustCoverageHashCString(strval.as_ptr()) }
-}
-
-pub(crate) fn hash_bytes(bytes: Vec<u8>) -> u64 {
+pub(crate) fn hash_bytes(bytes: &[u8]) -> u64 {
     unsafe { llvm::LLVMRustCoverageHashByteArray(bytes.as_ptr().cast(), bytes.len()) }
 }
 

compiler/rustc_codegen_llvm/src/llvm/ffi.rs

@@ -1916,7 +1916,6 @@ extern "C" {
     );
 
     pub fn LLVMRustCoverageCreatePGOFuncNameVar(F: &Value, FuncName: *const c_char) -> &Value;
-    pub fn LLVMRustCoverageHashCString(StrVal: *const c_char) -> u64;
     pub fn LLVMRustCoverageHashByteArray(Bytes: *const c_char, NumBytes: size_t) -> u64;
 
     #[allow(improper_ctypes)]

compiler/rustc_llvm/llvm-wrapper/CoverageMappingWrapper.cpp

@@ -158,14 +158,9 @@ extern "C" LLVMValueRef LLVMRustCoverageCreatePGOFuncNameVar(LLVMValueRef F, con
   return wrap(createPGOFuncNameVar(*cast<Function>(unwrap(F)), FuncNameRef));
 }
 
-extern "C" uint64_t LLVMRustCoverageHashCString(const char *StrVal) {
-  StringRef StrRef(StrVal);
-  return IndexedInstrProf::ComputeHash(StrRef);
-}
-
 extern "C" uint64_t LLVMRustCoverageHashByteArray(
     const char *Bytes,
-    unsigned NumBytes) {
+    size_t NumBytes) {
   StringRef StrRef(Bytes, NumBytes);
   return IndexedInstrProf::ComputeHash(StrRef);
 }