From 0eba65f0310d3c7d5516c7fd4c172d0bfa8b285b Mon Sep 17 00:00:00 2001 From: Miguel Ojeda Date: Tue, 6 Aug 2024 16:45:58 +0200 Subject: [PATCH] rust: x86: remove `-3dnow{,a}` from target features LLVM 19 is dropping support for 3DNow! in commit f0eb5587ceeb ("Remove support for 3DNow!, both intrinsics and builtins. (#96246)"): Remove support for 3DNow!, both intrinsics and builtins. (#96246) This set of instructions was only supported by AMD chips starting in the K6-2 (introduced 1998), and before the "Bulldozer" family (2011). They were never much used, as they were effectively superseded by the more-widely-implemented SSE (first implemented on the AMD side in Athlon XP in 2001). This is being done as a predecessor towards general removal of MMX register usage. Since there is almost no usage of the 3DNow! intrinsics, and no modern hardware even implements them, simple removal seems like the best option. Thus we should avoid passing these to the backend, since otherwise we get a diagnostic about it: '-3dnow' is not a recognized feature for this target (ignoring feature) '-3dnowa' is not a recognized feature for this target (ignoring feature) We could try to disable them only up to LLVM 19 (not the C side one, but the one used by `rustc`, which may be built with a range of LLVMs). However, to avoid more complexity, we can likely just remove them altogether. According to Nikita [2]: > I don't think it's needed because LLVM should not generate 3dnow > instructions unless specifically asked to, using intrinsics that > Rust does not provide in the first place. Thus do so, like Rust did for one of their builtin targets [3]. For those curious: Clang will warn only about trying to enable them (`-m3dnow{,a}`), but not about disabling them (`-mno-3dnow{,a}`), so there is no change needed there. Cc: Nikita Popov Cc: Nathan Chancellor Cc: x86@kernel.org Link: https://github.com/llvm/llvm-project/commit/f0eb5587ceeb641445b64cb264c822b4751de04a [1] Link: https://github.com/rust-lang/rust/pull/127864#issuecomment-2235898760 [2] Link: https://github.com/rust-lang/rust/pull/127864 [3] Closes: https://github.com/Rust-for-Linux/linux/issues/1094 Tested-by: Benno Lossin Tested-by: Alice Ryhl Link: https://lore.kernel.org/r/20240806144558.114461-1-ojeda@kernel.org Signed-off-by: Miguel Ojeda --- scripts/generate_rust_target.rs | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/scripts/generate_rust_target.rs b/scripts/generate_rust_target.rs index 87f34925eb7b..404edf7587e0 100644 --- a/scripts/generate_rust_target.rs +++ b/scripts/generate_rust_target.rs @@ -162,7 +162,7 @@ fn main() { "data-layout", "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-i128:128-f80:128-n8:16:32:64-S128", ); - let mut features = "-3dnow,-3dnowa,-mmx,+soft-float".to_string(); + let mut features = "-mmx,+soft-float".to_string(); if cfg.has("MITIGATION_RETPOLINE") { features += ",+retpoline-external-thunk"; } @@ -179,7 +179,7 @@ fn main() { "data-layout", "e-m:e-p:32:32-p270:32:32-p271:32:32-p272:64:64-i128:128-f64:32:64-f80:32-n8:16:32-S128", ); - let mut features = "-3dnow,-3dnowa,-mmx,+soft-float".to_string(); + let mut features = "-mmx,+soft-float".to_string(); if cfg.has("MITIGATION_RETPOLINE") { features += ",+retpoline-external-thunk"; }