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 https://github.com/rust-lang/rust/pull/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`  https://github.com/rust-lang/rust/pull/104000#discussion_r1014625377 and https://github.com/rust-lang/rust/pull/104000#discussion_r1014642482 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...

1 files changed, 21 insertions, 3 deletions

diff --git a/compiler/rustc_llvm/llvm-wrapper/RustWrapper.cpp b/compiler/rustc_llvm/llvm-wrapper/RustWrapper.cpp
index ab5fa961b95..870a2e02cba 100644
--- a/compiler/rustc_llvm/llvm-wrapper/RustWrapper.cpp
+++ b/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,