Rollup merge of #142809 - KMJ-007:ad-type-analysis-flag, r=ZuseZ4

Add PrintTAFn flag for targeted type analysis printing

## Summary
This PR adds a new `PrintTAFn` flag to the `-Z autodiff` option that allows printing type analysis information for a specific function, rather than all functions.

## Changes

### New Flag
- Added `PrintTAFn=<function_name>` option to `-Z autodiff`
- Usage: `-Z autodiff=Enable,PrintTAFn=my_function_name`

### Implementation Details
- **Rust side**: Added `PrintTAFn(String)` variant to `AutoDiff` enum
- **Parser**: Updated `parse_autodiff` to handle `PrintTAFn=<function_name>` syntax with proper error handling
- **FFI**: Added `set_print_type_fun` function to interface with Enzyme's `FunctionToAnalyze` command line option
- **Documentation**: Updated help text and documentation for the new flag

### Files Modified
- `compiler/rustc_session/src/config.rs`: Added `PrintTAFn(String)` variant
- `compiler/rustc_session/src/options.rs`: Updated parser and help text (now shows `PrintTAFn` in the list)
- `compiler/rustc_codegen_llvm/src/llvm/enzyme_ffi.rs`: Added FFI function and static variable
- `compiler/rustc_codegen_llvm/src/back/lto.rs`: Added handling for new flag
- `src/doc/rustc-dev-guide/src/autodiff/flags.md`: Updated documentation
- `src/doc/unstable-book/src/compiler-flags/autodiff.md`: Updated documentation

## Testing
The flag can be tested with:
```bash
rustc +enzyme -Z autodiff=Enable,PrintTAFn=square test.rs
```

This will print type analysis information only for the function named "square" instead of all functions.

## Error Handling
The parser includes proper error handling:
- Missing argument: `PrintTAFn` without `=<function_name>` will show an error
- Unknown options: Invalid autodiff options will be reported

r? ```@ZuseZ4```

Author: jdonszelmann

compiler/rustc_codegen_llvm/src/back/lto.rs

@@ -587,7 +587,7 @@ fn thin_lto(
 }
 
 fn enable_autodiff_settings(ad: &[config::AutoDiff]) {
-    for &val in ad {
+    for val in ad {
         // We intentionally don't use a wildcard, to not forget handling anything new.
         match val {
             config::AutoDiff::PrintPerf => {
@@ -599,6 +599,10 @@ fn enable_autodiff_settings(ad: &[config::AutoDiff]) {
             config::AutoDiff::PrintTA => {
                 llvm::set_print_type(true);
             }
+            config::AutoDiff::PrintTAFn(fun) => {
+                llvm::set_print_type(true); // Enable general type printing
+                llvm::set_print_type_fun(&fun); // Set specific function to analyze
+            }
             config::AutoDiff::Inline => {
                 llvm::set_inline(true);
             }

compiler/rustc_codegen_llvm/src/llvm/enzyme_ffi.rs

@@ -57,14 +57,19 @@ pub(crate) use self::Enzyme_AD::*;
 
 #[cfg(llvm_enzyme)]
 pub(crate) mod Enzyme_AD {
+    use std::ffi::{CString, c_char};
+
     use libc::c_void;
+
     unsafe extern "C" {
         pub(crate) fn EnzymeSetCLBool(arg1: *mut ::std::os::raw::c_void, arg2: u8);
+        pub(crate) fn EnzymeSetCLString(arg1: *mut ::std::os::raw::c_void, arg2: *const c_char);
     }
     unsafe extern "C" {
         static mut EnzymePrintPerf: c_void;
         static mut EnzymePrintActivity: c_void;
         static mut EnzymePrintType: c_void;
+        static mut EnzymeFunctionToAnalyze: c_void;
         static mut EnzymePrint: c_void;
         static mut EnzymeStrictAliasing: c_void;
         static mut looseTypeAnalysis: c_void;
@@ -86,6 +91,15 @@ pub(crate) mod Enzyme_AD {
             EnzymeSetCLBool(std::ptr::addr_of_mut!(EnzymePrintType), print as u8);
         }
     }
+    pub(crate) fn set_print_type_fun(fun_name: &str) {
+        let c_fun_name = CString::new(fun_name).unwrap();
+        unsafe {
+            EnzymeSetCLString(
+                std::ptr::addr_of_mut!(EnzymeFunctionToAnalyze),
+                c_fun_name.as_ptr() as *const c_char,
+            );
+        }
+    }
     pub(crate) fn set_print(print: bool) {
         unsafe {
             EnzymeSetCLBool(std::ptr::addr_of_mut!(EnzymePrint), print as u8);
@@ -132,6 +146,9 @@ pub(crate) mod Fallback_AD {
     pub(crate) fn set_print_type(print: bool) {
         unimplemented!()
     }
+    pub(crate) fn set_print_type_fun(fun_name: &str) {
+        unimplemented!()
+    }
     pub(crate) fn set_print(print: bool) {
         unimplemented!()
     }

compiler/rustc_session/src/config.rs

@@ -227,13 +227,15 @@ pub enum CoverageLevel {
 }
 
 /// The different settings that the `-Z autodiff` flag can have.
-#[derive(Clone, Copy, PartialEq, Hash, Debug)]
+#[derive(Clone, PartialEq, Hash, Debug)]
 pub enum AutoDiff {
     /// Enable the autodiff opt pipeline
     Enable,
 
     /// Print TypeAnalysis information
     PrintTA,
+    /// Print TypeAnalysis information for a specific function
+    PrintTAFn(String),
     /// Print ActivityAnalysis Information
     PrintAA,
     /// Print Performance Warnings from Enzyme

compiler/rustc_session/src/options.rs

@@ -725,7 +725,7 @@ mod desc {
     pub(crate) const parse_list: &str = "a space-separated list of strings";
     pub(crate) const parse_list_with_polarity: &str =
         "a comma-separated list of strings, with elements beginning with + or -";
-    pub(crate) const parse_autodiff: &str = "a comma separated list of settings: `Enable`, `PrintSteps`, `PrintTA`, `PrintAA`, `PrintPerf`, `PrintModBefore`, `PrintModAfter`, `PrintModFinal`, `PrintPasses`, `NoPostopt`, `LooseTypes`, `Inline`";
+    pub(crate) const parse_autodiff: &str = "a comma separated list of settings: `Enable`, `PrintSteps`, `PrintTA`, `PrintTAFn`, `PrintAA`, `PrintPerf`, `PrintModBefore`, `PrintModAfter`, `PrintModFinal`, `PrintPasses`, `NoPostopt`, `LooseTypes`, `Inline`";
     pub(crate) const parse_comma_list: &str = "a comma-separated list of strings";
     pub(crate) const parse_opt_comma_list: &str = parse_comma_list;
     pub(crate) const parse_number: &str = "a number";
@@ -1365,9 +1365,22 @@ pub mod parse {
         let mut v: Vec<&str> = v.split(",").collect();
         v.sort_unstable();
         for &val in v.iter() {
-            let variant = match val {
+            // Split each entry on '=' if it has an argument
+            let (key, arg) = match val.split_once('=') {
+                Some((k, a)) => (k, Some(a)),
+                None => (val, None),
+            };
+
+            let variant = match key {
                 "Enable" => AutoDiff::Enable,
                 "PrintTA" => AutoDiff::PrintTA,
+                "PrintTAFn" => {
+                    if let Some(fun) = arg {
+                        AutoDiff::PrintTAFn(fun.to_string())
+                    } else {
+                        return false;
+                    }
+                }
                 "PrintAA" => AutoDiff::PrintAA,
                 "PrintPerf" => AutoDiff::PrintPerf,
                 "PrintSteps" => AutoDiff::PrintSteps,

src/doc/rustc-dev-guide/src/autodiff/flags.md

@@ -6,6 +6,7 @@ To support you while debugging or profiling, we have added support for an experi
 
 ```text
 PrintTA // Print TypeAnalysis information
+PrintTAFn // Print TypeAnalysis information for a specific function
 PrintAA // Print ActivityAnalysis information
 Print // Print differentiated functions while they are being generated and optimized
 PrintPerf // Print AD related Performance warnings

src/doc/unstable-book/src/compiler-flags/autodiff.md

@@ -10,6 +10,7 @@ Multiple options can be separated with a comma. Valid options are:
 
 `Enable` - Required flag to enable autodiff
 `PrintTA` - print Type Analysis Information
+`PrintTAFn` - print Type Analysis Information for a specific function
 `PrintAA` - print Activity Analysis Information
 `PrintPerf` - print Performance Warnings from Enzyme
 `PrintSteps` - prints all intermediate transformations