compiletest: add max-llvm-version directive

There's already `min-llvm-version`, and contributors were using
`ignore-llvm-versions: 20 - 99` to emulate `max-llvm-version: 19`.

Author: jieyouxu

src/tools/compiletest/src/command-list.rs

@@ -116,6 +116,7 @@ const KNOWN_DIRECTIVE_NAMES: &[&str] = &[
     "incremental",
     "known-bug",
     "llvm-cov-flags",
+    "max-llvm-version",
     "min-cdb-version",
     "min-gdb-version",
     "min-lldb-version",

src/tools/compiletest/src/header.rs

@@ -1501,6 +1501,17 @@ fn ignore_llvm(config: &Config, line: &str) -> IgnoreDecision {
                     ),
                 };
             }
+        } else if let Some(value) = config.parse_name_value_directive(line, "max-llvm-version") {
+            let value = value.trim();
+            let max_version = extract_llvm_version(value).unwrap();
+            // Ignore if actual version is larger than the maximum required version.
+            if actual_version > max_version {
+                return IgnoreDecision::Ignore {
+                    reason: format!(
+                        "ignored when the LLVM version ({actual_version}) is newer than {max_version}"
+                    ),
+                };
+            }
         } else if let Some(value) =
             config.parse_name_value_directive(line, "min-system-llvm-version")
         {

src/tools/compiletest/src/header/tests.rs

@@ -261,6 +261,15 @@ fn llvm_version() {
 
     let config: Config = cfg().llvm_version("10.0.0").build();
     assert!(!check_ignore(&config, "//@ min-llvm-version: 9.0"));
+
+    let config: Config = cfg().llvm_version("20.0.0").build();
+    assert!(check_ignore(&config, "//@ max-llvm-version: 19.3.1"));
+
+    let config: Config = cfg().llvm_version("20.0.0").build();
+    assert!(!check_ignore(&config, "//@ max-llvm-version: 20.0.0"));
+
+    let config: Config = cfg().llvm_version("20.0.0").build();
+    assert!(!check_ignore(&config, "//@ max-llvm-version: 20.0.1"));
 }
 
 #[test]