Auto merge of #124676 - djkoloski:relax_multiple_sanitizers, r=cuviper,rcvalle

Relax restrictions on multiple sanitizers

Most combinations of LLVM sanitizers are legal-enough to enable simultaneously. This change will allow simultaneously enabling ASAN and shadow call stacks on supported platforms.

I used this python script to generate the mutually-exclusive sanitizer combinations:

```python
#!/usr/bin/python3

import subprocess

flags = [
    ["-fsanitize=address"],
    ["-fsanitize=leak"],
    ["-fsanitize=memory"],
    ["-fsanitize=thread"],
    ["-fsanitize=hwaddress"],
    ["-fsanitize=cfi", "-flto", "-fvisibility=hidden"],
    ["-fsanitize=memtag", "--target=aarch64-linux-android", "-march=armv8a+memtag"],
    ["-fsanitize=shadow-call-stack"],
    ["-fsanitize=kcfi", "-flto", "-fvisibility=hidden"],
    ["-fsanitize=kernel-address"],
    ["-fsanitize=safe-stack"],
    ["-fsanitize=dataflow"],
]

for i in range(len(flags)):
    for j in range(i):
        command = ["clang++"] + flags[i] + flags[j] + ["-o", "main.o", "-c", "main.cpp"]
        completed = subprocess.run(command, stderr=subprocess.DEVNULL)
        if completed.returncode != 0:
            first = flags[i][0][11:].replace('-', '').upper()
            second = flags[j][0][11:].replace('-', '').upper()
            print(f"(SanitizerSet::{first}, SanitizerSet::{second}),")
```

1 files changed, 3 insertions, 11 deletions

diff --git a/compiler/rustc_session/src/session.rs b/compiler/rustc_session/src/session.rs
index db01bb90d6f..a2872fc1661 100644
--- a/compiler/rustc_session/src/session.rs
+++ b/compiler/rustc_session/src/session.rs
@@ -1183,9 +1183,9 @@ fn validate_commandline_args_with_session_available(sess: &Session) {
             });
         }
     }
-    // Cannot mix and match sanitizers.
-    let mut sanitizer_iter = sess.opts.unstable_opts.sanitizer.into_iter();
-    if let (Some(first), Some(second)) = (sanitizer_iter.next(), sanitizer_iter.next()) {
+
+    // Cannot mix and match mutually-exclusive sanitizers.
+    if let Some((first, second)) = sess.opts.unstable_opts.sanitizer.mutually_exclusive() {
         sess.dcx().emit_err(errors::CannotMixAndMatchSanitizers {
             first: first.to_string(),
             second: second.to_string(),
@@ -1220,14 +1220,6 @@ fn validate_commandline_args_with_session_available(sess: &Session) {
         sess.dcx().emit_err(errors::SanitizerCfiRequiresSingleCodegenUnit);
     }
 
-    // LLVM CFI is incompatible with LLVM KCFI.
-    if sess.is_sanitizer_cfi_enabled() && sess.is_sanitizer_kcfi_enabled() {
-        sess.dcx().emit_err(errors::CannotMixAndMatchSanitizers {
-            first: "cfi".to_string(),
-            second: "kcfi".to_string(),
-        });
-    }
-
     // Canonical jump tables requires CFI.
     if sess.is_sanitizer_cfi_canonical_jump_tables_disabled() {
         if !sess.is_sanitizer_cfi_enabled() {