From e89c9ff4c0e80ba90e6700ee31786408da7c1cf4 Mon Sep 17 00:00:00 2001
From: Ralf Jung <post@ralfj.de>
Date: Thu, 26 Dec 2024 19:47:41 +0100
Subject: [PATCH] x86-64 hardfloat actually requires sse2

---
 compiler/rustc_codegen_gcc/src/gcc_util.rs    | 18 ++++++++++++------
 compiler/rustc_codegen_llvm/src/llvm_util.rs  | 19 +++++++++++++------
 compiler/rustc_target/src/target_features.rs  | 11 ++++++++++-
 tests/codegen/target-feature-overrides.rs     |  4 ++--
 ...oat-target-feature-flag-disable-implied.rs | 10 ++++++++++
 ...target-feature-flag-disable-implied.stderr |  7 +++++++
 6 files changed, 54 insertions(+), 15 deletions(-)
 create mode 100644 tests/ui/target-feature/forbidden-hardfloat-target-feature-flag-disable-implied.rs
 create mode 100644 tests/ui/target-feature/forbidden-hardfloat-target-feature-flag-disable-implied.stderr

diff --git a/compiler/rustc_codegen_gcc/src/gcc_util.rs b/compiler/rustc_codegen_gcc/src/gcc_util.rs
index 3388a6e78a33f..f000cc98920c0 100644
--- a/compiler/rustc_codegen_gcc/src/gcc_util.rs
+++ b/compiler/rustc_codegen_gcc/src/gcc_util.rs
@@ -129,12 +129,18 @@ pub(crate) fn global_gcc_features(sess: &Session, diagnostics: bool) -> Vec<Stri
                     });
                 }
             } else {
-                if abi_enable_set.contains(feature) {
-                    sess.dcx().emit_warn(ForbiddenCTargetFeature {
-                        feature,
-                        enabled: "disabled",
-                        reason: "this feature is required by the target ABI",
-                    });
+                // FIXME: we have to request implied features here since
+                // negative features do not handle implied features above.
+                #[allow(rustc::potential_query_instability)] // order does not matter
+                for &required in abi_enable_set.iter() {
+                    let implied = sess.target.implied_target_features(std::iter::once(required));
+                    if implied.contains(feature) {
+                        sess.dcx().emit_warn(ForbiddenCTargetFeature {
+                            feature,
+                            enabled: "disabled",
+                            reason: "this feature is required by the target ABI",
+                        });
+                    }
                 }
             }
 
diff --git a/compiler/rustc_codegen_llvm/src/llvm_util.rs b/compiler/rustc_codegen_llvm/src/llvm_util.rs
index d4b2260123b0c..7fe0624e16651 100644
--- a/compiler/rustc_codegen_llvm/src/llvm_util.rs
+++ b/compiler/rustc_codegen_llvm/src/llvm_util.rs
@@ -753,12 +753,19 @@ pub(crate) fn global_llvm_features(
                         });
                     }
                 } else {
-                    if abi_enable_set.contains(feature) {
-                        sess.dcx().emit_warn(ForbiddenCTargetFeature {
-                            feature,
-                            enabled: "disabled",
-                            reason: "this feature is required by the target ABI",
-                        });
+                    // FIXME: we have to request implied features here since
+                    // negative features do not handle implied features above.
+                    #[allow(rustc::potential_query_instability)] // order does not matter
+                    for &required in abi_enable_set.iter() {
+                        let implied =
+                            sess.target.implied_target_features(std::iter::once(required));
+                        if implied.contains(feature) {
+                            sess.dcx().emit_warn(ForbiddenCTargetFeature {
+                                feature,
+                                enabled: "disabled",
+                                reason: "this feature is required by the target ABI",
+                            });
+                        }
                     }
                 }
 
diff --git a/compiler/rustc_target/src/target_features.rs b/compiler/rustc_target/src/target_features.rs
index a9244174b17e0..2a07c675cfa10 100644
--- a/compiler/rustc_target/src/target_features.rs
+++ b/compiler/rustc_target/src/target_features.rs
@@ -754,7 +754,7 @@ impl Target {
         // "forbidden" in the list above to ensure that there is a consistent answer to the
         // questions "which ABI is used".
         match &*self.arch {
-            "x86" | "x86_64" => {
+            "x86" => {
                 // We support 2 ABIs, hardfloat (default) and softfloat.
                 if self.has_feature("soft-float") {
                     NOTHING
@@ -763,6 +763,15 @@ impl Target {
                     (&["x87"], &[])
                 }
             }
+            "x86_64" => {
+                // We support 2 ABIs, hardfloat (default) and softfloat.
+                if self.has_feature("soft-float") {
+                    NOTHING
+                } else {
+                    // Hardfloat ABI. x87 and SSE2 must be enabled.
+                    (&["x87", "sse2"], &[])
+                }
+            }
             "arm" => {
                 // We support 2 ABIs, hardfloat (default) and softfloat.
                 if self.has_feature("soft-float") {
diff --git a/tests/codegen/target-feature-overrides.rs b/tests/codegen/target-feature-overrides.rs
index f38a1ae72de5d..c4f9a8898a1fb 100644
--- a/tests/codegen/target-feature-overrides.rs
+++ b/tests/codegen/target-feature-overrides.rs
@@ -40,7 +40,7 @@ pub unsafe fn banana() -> u32 {
 
 // CHECK: attributes [[APPLEATTRS]]
 // COMPAT-SAME: "target-features"="+avx,+avx2,{{.*}}"
-// INCOMPAT-SAME: "target-features"="-avx2,-avx,+avx,{{.*}}"
+// INCOMPAT-SAME: "target-features"="-avx2,-avx,+x87,+sse2,+avx,{{.*}}"
 // CHECK: attributes [[BANANAATTRS]]
 // COMPAT-SAME: "target-features"="+avx,+avx2,{{.*}}"
-// INCOMPAT-SAME: "target-features"="-avx2,-avx"
+// INCOMPAT-SAME: "target-features"="-avx2,-avx,+x87,+sse2"
diff --git a/tests/ui/target-feature/forbidden-hardfloat-target-feature-flag-disable-implied.rs b/tests/ui/target-feature/forbidden-hardfloat-target-feature-flag-disable-implied.rs
new file mode 100644
index 0000000000000..3d09217327ab9
--- /dev/null
+++ b/tests/ui/target-feature/forbidden-hardfloat-target-feature-flag-disable-implied.rs
@@ -0,0 +1,10 @@
+//@ compile-flags: --target=x86_64-unknown-linux-gnu --crate-type=lib
+//@ needs-llvm-components: x86
+//@ compile-flags: -Ctarget-feature=-sse
+// For now this is just a warning.
+//@ build-pass
+#![feature(no_core, lang_items)]
+#![no_core]
+
+#[lang = "sized"]
+pub trait Sized {}
diff --git a/tests/ui/target-feature/forbidden-hardfloat-target-feature-flag-disable-implied.stderr b/tests/ui/target-feature/forbidden-hardfloat-target-feature-flag-disable-implied.stderr
new file mode 100644
index 0000000000000..72b2d03fe2036
--- /dev/null
+++ b/tests/ui/target-feature/forbidden-hardfloat-target-feature-flag-disable-implied.stderr
@@ -0,0 +1,7 @@
+warning: target feature `sse` cannot be disabled with `-Ctarget-feature`: this feature is required by the target ABI
+   |
+   = note: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+   = note: for more information, see issue #116344 <https://github.com/rust-lang/rust/issues/116344>
+
+warning: 1 warning emitted
+