lang/rust: enable SSE2 by default on i386

Upstream Rust always requires SSE2 for x86.  But back in 2017[^1][^2] we
patched lang/rust to disable SSE2 for i386.  At the time, it was
reported that some people were still using non-SSE2 capable hardware.
More recently, LLVM bugs have been discovered[^3][^4] that can result in
rounding bugs and reduced accuracy when using f64 on non-SSE hardware.
In weird cases, they can even cause wilder unpredictable behavior, like
segfaults.

Revert our change for the sake of Pentium 4 (and later) users.  But add
an SSE2 option.  Disabling it will allow the port to be used on Pentium
3 and older CPUs.

[^1]: d65b288
[^2]: https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=223415
[^3]: rust-lang/rust#114479
[^4]: llvm/llvm-project#44218

Reviewed by: emaste
Differential Revision: https://reviews.freebsd.org/D47227

UPDATING

@@ -5,6 +5,18 @@ they are unavoidable.
 You should get into the habit of checking this file for changes each time
 you update your ports collection, before attempting any port upgrades.
 
+20241109:
+  AFFECTS: all users of i386
+  AUTHOR: asomers@FreeBSD.org
+
+  On i386 the lang/rust port has been updated to require SSE2 by default.  Not
+  only does the compiler itself require SSE2, but it unconditionally generates
+  code that requires it, too.  Over 500 ports include Rust code (www/firefox,
+  security/py-cryptography, etc).  Official binary packages of all of those
+  ports will no longer work on Pentium III and older hardware.  PIII users must
+  now build their own lang/rust packages, clearing the SSE2 option, and rebuild
+  any dependent ports.
+
 20241104:
   AFFECTS: users of mail/fetchmail
   AUTHOR: chalpin@cs.wisc.edu

lang/rust/Makefile

@@ -1,6 +1,6 @@
 PORTNAME=	rust
 PORTVERSION?=	1.82.0
-PORTREVISION?=	0
+PORTREVISION?=	1
 CATEGORIES=	lang
 MASTER_SITES=	https://static.rust-lang.org/dist/:src \
 		https://dev-static.rust-lang.org/dist/:src \
@@ -48,12 +48,17 @@ TMPDIR?=	${WRKDIR}
 
 OPTIONS_DEFINE=		DOCS GDB LTO PORT_LLVM SOURCES WASM
 OPTIONS_DEFAULT=	SOURCES WASM
+OPTIONS_DEFINE_i386=	SSE2
+OPTIONS_DEFAULT_i386=	SSE2
 
 GDB_DESC=	Install ports gdb (necessary for debugging rust programs)
 PORT_LLVM_DESC=	Build against devel/llvm instead of bundled copy (experimental)
+SSE2_DESC=	Enable SSE2 instructions
 SOURCES_DESC=	Install source files
 WASM_DESC=	Build the WebAssembly target (wasm32-unknown-unknown)
 
+SSE2_EXTRA_PATCHES_OFF+=	${FILESDIR}/extra-patch-compiler_rustc__target_src_spec_targets_i686__unknown__freebsd.rs
+
 DOCS_VARS=		_RUST_BUILD_DOCS=true \
 			_COMPONENTS+="rust-docs-${_PACKAGE_VERS}-${_RUST_TARGET} rust-docs-json-${_PACKAGE_VERS}-${_RUST_TARGET}" \
 			_RUST_TOOLS+=rustdoc