Add support for //@ ignore-i586

There are a few tests that were trying to skip i586 targets via the `TARGET`
environment variable instead, so better to just add support for the directive.

src/tools/compiletest/src/common.rs

@@ -701,10 +701,13 @@ impl Config {
     }
 
     pub fn matches_arch(&self, arch: &str) -> bool {
-        self.target_cfg().arch == arch ||
-        // Matching all the thumb variants as one can be convenient.
-        // (thumbv6m, thumbv7em, thumbv7m, etc.)
-        (arch == "thumb" && self.target.starts_with("thumb"))
+        self.target_cfg().arch == arch
+            || {
+                // Matching all the thumb variants as one can be convenient.
+                // (thumbv6m, thumbv7em, thumbv7m, etc.)
+                arch == "thumb" && self.target.starts_with("thumb")
+            }
+            || (arch == "i586" && self.target.starts_with("i586-"))
     }
 
     pub fn matches_os(&self, os: &str) -> bool {

src/tools/compiletest/src/directives/cfg.rs

@@ -166,6 +166,14 @@ fn parse_cfg_name_directive<'a>(
         message: "when the architecture is part of the Thumb family"
     }
 
+    // The "arch" of `i586-` targets is "x86", so for more specific matching
+    // we have to resort to a string-prefix check.
+    condition! {
+        name: "i586",
+        condition: config.matches_arch("i586"),
+        message: "when the subarchitecture is i586",
+    }
+
     condition! {
         name: "apple",
         condition: config.target.contains("apple"),

src/tools/compiletest/src/directives/directive_names.rs

@@ -70,6 +70,7 @@ pub(crate) const KNOWN_DIRECTIVE_NAMES: &[&str] = &[
     "ignore-gnu",
     "ignore-haiku",
     "ignore-horizon",
+    "ignore-i586",
     "ignore-i686-pc-windows-gnu",
     "ignore-i686-pc-windows-msvc",
     "ignore-illumos",

src/tools/compiletest/src/directives/tests.rs

@@ -605,6 +605,8 @@ fn ignore_arch() {
         ("i686-unknown-linux-gnu", "x86"),
         ("nvptx64-nvidia-cuda", "nvptx64"),
         ("thumbv7m-none-eabi", "thumb"),
+        ("i586-unknown-linux-gnu", "x86"),
+        ("i586-unknown-linux-gnu", "i586"),
     ];
     for (target, arch) in archs {
         let config: Config = cfg().target(target).build();

tests/assembly-llvm/x86-return-float.rs

@@ -1,9 +1,6 @@
 //@ assembly-output: emit-asm
 // FIXME(#114479): LLVM miscompiles loading and storing `f32` and `f64` when SSE is disabled.
-// There's no compiletest directive to ignore a test on i586 only, so just always explicitly enable
-// SSE2.
-// Use the same target CPU as `i686` so that LLVM orders the instructions in the same order.
-//@ compile-flags: -Ctarget-feature=+sse2 -Ctarget-cpu=pentium4
+// (As of #136758, this test cross-compiles to selected i686 targets only, which have SSE.)
 // Force frame pointers to make ASM more consistent between targets
 //@ compile-flags: -C force-frame-pointers
 // At opt-level=3, LLVM can merge two movss into one movsd, and we aren't testing for that.

tests/ui/abi/homogenous-floats-target-feature-mixup.rs

@@ -7,6 +7,7 @@
 //@ run-pass
 //@ needs-subprocess
 //@ ignore-backends: gcc
+//@ ignore-i586 (no SSE2)
 
 #![allow(overflowing_literals)]
 #![allow(unused_variables)]
@@ -19,16 +20,6 @@ fn main() {
         return test::main(&level)
     }
 
-    match std::env::var("TARGET") {
-        Ok(s) => {
-            // Skip this tests on i586-unknown-linux-gnu where sse2 is disabled
-            if s.contains("i586") {
-                return
-            }
-        }
-        Err(_) => return,
-    }
-
     let me = env::current_exe().unwrap();
     for level in ["sse", "avx", "avx512"].iter() {
         let status = Command::new(&me).arg(level).status().unwrap();

tests/ui/target-feature/target-feature-detection.rs

@@ -2,22 +2,12 @@
 //! specifically `sse2` on x86/x86_64 platforms, and correctly reports absent features.
 
 //@ run-pass
+//@ ignore-i586 (no SSE2)
 
 #![allow(stable_features)]
 #![feature(cfg_target_feature)]
 
-use std::env;
-
 fn main() {
-    match env::var("TARGET") {
-        Ok(s) => {
-            // Skip this tests on i586-unknown-linux-gnu where sse2 is disabled
-            if s.contains("i586") {
-                return;
-            }
-        }
-        Err(_) => return,
-    }
     if cfg!(any(target_arch = "x86", target_arch = "x86_64")) {
         assert!(
             cfg!(target_feature = "sse2"),