Rollup merge of #113723 - khei4:khei4/llvm-stats, r=oli-obk,nikic

Resurrect: rustc_llvm: Add a -Z `print-codegen-stats` option to expose LLVM statistics.

This resurrects PR #104000, which has sat idle for a while. And I want to see the effect of stack-move optimizations on LLVM (like https://reviews.llvm.org/D153453) :).

I have applied the changes requested by `@oli-obk` and `@nagisa`  #104000 (comment) and #104000 (comment) in the latest commits.

r? `@oli-obk`

-----

LLVM has a neat [statistics](https://llvm.org/docs/ProgrammersManual.html#the-statistic-class-stats-option) feature that tracks how often optimizations kick in. It's very handy for optimization work. Since we expose the LLVM pass timings, I thought it made sense to expose the LLVM statistics too.

-----
(Edit: fix broken link
(Edit2: fix segmentation fault and use malloc

If `rustc` is built with
```toml
[llvm]
assertions = true
```
Then you can see like
```
rustc +stage1 -Z print-codegen-stats -C opt-level=3  tmp.rs
===-------------------------------------------------------------------------===
                          ... Statistics Collected ...
===-------------------------------------------------------------------------===
         3 aa                           - Number of MayAlias results
       193 aa                           - Number of MustAlias results
       531 aa                           - Number of NoAlias results
...
```

And the current default build emits only
```
$ rustc +stage1 -Z print-codegen-stats -C opt-level=3  tmp.rs
===-------------------------------------------------------------------------===
                          ... Statistics Collected ...
===-------------------------------------------------------------------------===
$
```
This might be better to emit the message to tell assertion flag necessity, but now I can't find how to do that...

compiler/rustc_codegen_gcc/src/lib.rs

@@ -239,6 +239,10 @@ impl WriteBackendMethods for GccCodegenBackend {
         unimplemented!();
     }
 
+    fn print_statistics(&self) {
+        unimplemented!()
+    }
+
     unsafe fn optimize(_cgcx: &CodegenContext<Self>, _diag_handler: &Handler, module: &ModuleCodegen<Self::Module>, config: &ModuleConfig) -> Result<(), FatalError> {
         module.module_llvm.context.set_optimization_level(to_gcc_opt_level(config.opt_level));
         Ok(())

compiler/rustc_codegen_llvm/src/lib.rs

@@ -46,6 +46,7 @@ use rustc_span::symbol::Symbol;
 
 use std::any::Any;
 use std::ffi::CStr;
+use std::io::Write;
 
 mod back {
     pub mod archive;
@@ -178,7 +179,28 @@ impl WriteBackendMethods for LlvmCodegenBackend {
     type ThinBuffer = back::lto::ThinBuffer;
     fn print_pass_timings(&self) {
         unsafe {
-            llvm::LLVMRustPrintPassTimings();
+            let mut size = 0;
+            let cstr = llvm::LLVMRustPrintPassTimings(&mut size as *mut usize);
+            if cstr.is_null() {
+                println!("failed to get pass timings");
+            } else {
+                let timings = std::slice::from_raw_parts(cstr as *const u8, size);
+                std::io::stdout().write_all(timings).unwrap();
+                libc::free(cstr as *mut _);
+            }
+        }
+    }
+    fn print_statistics(&self) {
+        unsafe {
+            let mut size = 0;
+            let cstr = llvm::LLVMRustPrintStatistics(&mut size as *mut usize);
+            if cstr.is_null() {
+                println!("failed to get pass stats");
+            } else {
+                let stats = std::slice::from_raw_parts(cstr as *const u8, size);
+                std::io::stdout().write_all(stats).unwrap();
+                libc::free(cstr as *mut _);
+            }
         }
     }
     fn run_link(

compiler/rustc_codegen_llvm/src/llvm/ffi.rs

@@ -1868,7 +1868,10 @@ extern "C" {
     pub fn LLVMRustGetLastError() -> *const c_char;
 
     /// Print the pass timings since static dtors aren't picking them up.
-    pub fn LLVMRustPrintPassTimings();
+    pub fn LLVMRustPrintPassTimings(size: *const size_t) -> *const c_char;
+
+    /// Print the statistics since static dtors aren't picking them up.
+    pub fn LLVMRustPrintStatistics(size: *const size_t) -> *const c_char;
 
     pub fn LLVMStructCreateNamed(C: &Context, Name: *const c_char) -> &Type;
 

compiler/rustc_codegen_llvm/src/llvm_util.rs

@@ -110,6 +110,10 @@ unsafe fn configure_llvm(sess: &Session) {
         // Use non-zero `import-instr-limit` multiplier for cold callsites.
         add("-import-cold-multiplier=0.1", false);
 
+        if sess.print_llvm_stats() {
+            add("-stats", false);
+        }
+
         for arg in sess_args {
             add(&(*arg), true);
         }

compiler/rustc_codegen_ssa/src/back/write.rs

@@ -1945,6 +1945,10 @@ impl<B: ExtraBackendMethods> OngoingCodegen<B> {
             self.backend.print_pass_timings()
         }
 
+        if sess.print_llvm_stats() {
+            self.backend.print_statistics()
+        }
+
         (
             CodegenResults {
                 metadata: self.metadata,

compiler/rustc_codegen_ssa/src/traits/write.rs

@@ -35,6 +35,7 @@ pub trait WriteBackendMethods: 'static + Sized + Clone {
         cached_modules: Vec<(SerializedModule<Self::ModuleBuffer>, WorkProduct)>,
     ) -> Result<(Vec<LtoModuleCodegen<Self>>, Vec<WorkProduct>), FatalError>;
     fn print_pass_timings(&self);
+    fn print_statistics(&self);
     unsafe fn optimize(
         cgcx: &CodegenContext<Self>,
         diag_handler: &Handler,

compiler/rustc_interface/src/tests.rs

@@ -715,6 +715,7 @@ fn test_unstable_options_tracking_hash() {
     untracked!(perf_stats, true);
     // `pre_link_arg` is omitted because it just forwards to `pre_link_args`.
     untracked!(pre_link_args, vec![String::from("abc"), String::from("def")]);
+    untracked!(print_codegen_stats, true);
     untracked!(print_llvm_passes, true);
     untracked!(print_mono_items, Some(String::from("abc")));
     untracked!(print_type_sizes, true);

compiler/rustc_llvm/llvm-wrapper/RustWrapper.cpp

@@ -1,4 +1,5 @@
 #include "LLVMWrapper.h"
+#include "llvm/ADT/Statistic.h"
 #include "llvm/IR/DebugInfoMetadata.h"
 #include "llvm/IR/DiagnosticHandler.h"
 #include "llvm/IR/DiagnosticInfo.h"
@@ -111,9 +112,26 @@ extern "C" void LLVMRustSetNormalizedTarget(LLVMModuleRef M,
   unwrap(M)->setTargetTriple(Triple::normalize(Triple));
 }
 
-extern "C" void LLVMRustPrintPassTimings() {
-  raw_fd_ostream OS(2, false); // stderr.
-  TimerGroup::printAll(OS);
+extern "C" const char *LLVMRustPrintPassTimings(size_t *Len) {
+  std::string buf;
+  raw_string_ostream SS(buf);
+  TimerGroup::printAll(SS);
+  SS.flush();
+  *Len = buf.length();
+  char *CStr = (char *)malloc(*Len);
+  memcpy(CStr, buf.c_str(), *Len);
+  return CStr;
+}
+
+extern "C" const char *LLVMRustPrintStatistics(size_t *Len) {
+  std::string buf;
+  raw_string_ostream SS(buf);
+  llvm::PrintStatistics(SS);
+  SS.flush();
+  *Len = buf.length();
+  char *CStr = (char *)malloc(*Len);
+  memcpy(CStr, buf.c_str(), *Len);
+  return CStr;
 }
 
 extern "C" LLVMValueRef LLVMRustGetNamedValue(LLVMModuleRef M, const char *Name,

compiler/rustc_session/src/options.rs

@@ -1668,6 +1668,9 @@ options! {
         "use a more precise version of drop elaboration for matches on enums (default: yes). \
         This results in better codegen, but has caused miscompilations on some tier 2 platforms. \
         See #77382 and #74551."),
+    #[rustc_lint_opt_deny_field_access("use `Session::print_codegen_stats` instead of this field")]
+    print_codegen_stats: bool = (false, parse_bool, [UNTRACKED],
+        "print codegen statistics (default: no)"),
     print_fuel: Option<String> = (None, parse_opt_string, [TRACKED],
         "make rustc print the total optimization fuel used by a crate"),
     print_llvm_passes: bool = (false, parse_bool, [UNTRACKED],

compiler/rustc_session/src/session.rs

@@ -1057,6 +1057,10 @@ impl Session {
         self.opts.unstable_opts.verbose
     }
 
+    pub fn print_llvm_stats(&self) -> bool {
+        self.opts.unstable_opts.print_codegen_stats
+    }
+
     pub fn verify_llvm_ir(&self) -> bool {
         self.opts.unstable_opts.verify_llvm_ir || option_env!("RUSTC_VERIFY_LLVM_IR").is_some()
     }