Add option to emit compiler stderr per bitwidth.

src/tools/compiletest/src/header.rs

@@ -333,6 +333,8 @@ pub struct TestProps {
     pub assembly_output: Option<String>,
     // If true, the test is expected to ICE
     pub should_ice: bool,
+    // If true, the stderr is expected to be different across bit-widths.
+    pub stderr_per_bitwidth: bool,
 }
 
 impl TestProps {
@@ -372,6 +374,7 @@ impl TestProps {
             rustfix_only_machine_applicable: false,
             assembly_output: None,
             should_ice: false,
+            stderr_per_bitwidth: false,
         }
     }
 
@@ -538,6 +541,10 @@ impl TestProps {
                 if self.assembly_output.is_none() {
                     self.assembly_output = config.parse_assembly_output(ln);
                 }
+
+                if !self.stderr_per_bitwidth {
+                    self.stderr_per_bitwidth = config.parse_stderr_per_bitwidth(ln);
+                }
             });
         }
 
@@ -774,6 +781,10 @@ impl Config {
         self.parse_name_directive(line, "ignore-pass")
     }
 
+    fn parse_stderr_per_bitwidth(&self, line: &str) -> bool {
+        self.parse_name_directive(line, "stderr-per-bitwidth")
+    }
+
     fn parse_assembly_output(&self, line: &str) -> Option<String> {
         self.parse_name_value_directive(line, "assembly-output").map(|r| r.trim().to_string())
     }

src/tools/compiletest/src/runtest.rs

@@ -3124,7 +3124,12 @@ impl<'test> TestCx<'test> {
                     errors += self.compare_output("stdout", &normalized_stdout, &expected_stdout);
                 }
                 if !self.props.dont_check_compiler_stderr {
-                    errors += self.compare_output("stderr", &normalized_stderr, &expected_stderr);
+                    let kind = if self.props.stderr_per_bitwidth {
+                        format!("{}bit.stderr", get_pointer_width(&self.config.target))
+                    } else {
+                        String::from("stderr")
+                    };
+                    errors += self.compare_output(&kind, &normalized_stderr, &expected_stderr);
                 }
             }
             TestOutput::Run => {