Use LTO build of libunwind if using -Clinker-plugin-lto

This greatly reduces binary sizes, at the expense of compilation speed.
Normal builds still use a regular non-LTO build of libunwind.

Author: overdrivenpotato

libunwind/.gitignore

@@ -1,4 +1,4 @@
 src
 include
-libunwind.a
+libunwind*.a
 *.o

libunwind/Makefile

@@ -1,3 +1,8 @@
+SUFFIX ?=
+CPPFLAGS ?=
+
+OUTLIB := libunwind$(SUFFIX).a
+
 CC      := clang
 CXX     := clang++
 AR      := llvm-ar
@@ -9,20 +14,25 @@ S_OBJLIST   := UnwindRegistersRestore.o UnwindRegistersSave.o
 
 CFLAGS   := -std=c99
 CXXFLAGS := -std=c++11 -nostdinc++ -fno-exceptions -fno-rtti
-CPPFLAGS := -target mipsel-unknown-unknown -mcpu=mips2 -msingle-float \
-	-fstrict-aliasing -funwind-tables -O3 \
+CPPFLAGS := $(CPPFLAGS) -target mipsel-unknown-unknown -mcpu=mips2 \
+	-msingle-float -fstrict-aliasing -funwind-tables -O3 \
 	-D __LITTLE_ENDIAN__ -D __ELF__ -D _LIBUNWIND_IS_BAREMETAL \
 	-D _LIBUNWIND_HAS_NO_THREADS -D _LIBUNWIND_IS_NATIVE_ONLY \
 	-DNDEBUG \
 	-I /usr/local/pspdev/psp/include/ \
 	-I include
 
-../psp/libunwind.a: libunwind.a
-	cp libunwind.a ../psp/
+all:
+	make ../psp/libunwind.a
+	SUFFIX=_lto CPPFLAGS=-flto make ../psp/libunwind_lto.a
+
+../psp/$(OUTLIB): $(OUTLIB)
+	cp $^ ../psp/
 	touch ../psp/build.rs
+	make clean
 
-libunwind.a: $(CPP_OBJLIST) $(C_OBJLIST) $(S_OBJLIST)
-	$(AR) $(ARFLAGS) libunwind.a $^
+$(OUTLIB): $(CPP_OBJLIST) $(C_OBJLIST) $(S_OBJLIST)
+	$(AR) $(ARFLAGS) $(OUTLIB) $^
 
 $(CPP_OBJLIST): %.o: src/%.cpp
 	$(COMPILE.cc) $^
@@ -32,7 +42,7 @@ $(S_OBJLIST): %.o: src/%.S
 $(C_OBJLIST) $(S_OBJLIST):
 	$(COMPILE.c) $^
 
-.PHONY: clean patch
+.PHONY: all clean patch
 
 patch:
 	git submodule update --init --depth 1 -- ./rustc
@@ -41,4 +51,4 @@ patch:
 	patch -p0 < ./no-sdc1.patch
 
 clean:
-	rm -r *.o libunwind.a
+	rm -r *.o

psp/build.rs

@@ -1,18 +1,31 @@
-use std::{env, path::Path};
+use std::{env, path::Path, os::unix::prelude::OsStrExt};
 
 fn main() {
     println!("cargo:rerun-if-changed=build.rs");
     println!("cargo:rerun-if-changed=libunwind.a");
+    println!("cargo:rerun-if-env-changed=RUSTFLAGS");
 
     if env::var("CARGO_FEATURE_STUB_ONLY").is_ok() {
         return;
     }
 
+    // Figure out whether to use the LTO libunwind, or the regular one.
+    let libunwind = if env::var_os("CARGO_ENCODED_RUSTFLAGS")
+        .expect("could not get `CARGO_ENCODED_RUSTFLAGS` variable")
+        .as_bytes()
+        .split(|b| *b == 0x1f)
+        .any(|flags| flags.starts_with(b"-Clinker-plugin-lto"))
+    {
+        "./libunwind_lto.a"
+    } else {
+        "./libunwind.a"
+    };
+
     // TODO: Do we even need to copy the library over? Maybe we can just link
     // directly from the current directory.
     let out_dir = env::var("OUT_DIR").unwrap();
     let out_file = Path::new(&out_dir).join("libunwind.a");
-    std::fs::copy("./libunwind.a", out_file).unwrap();
+    std::fs::copy(libunwind, out_file).unwrap();
 
     println!("cargo:rustc-link-lib=static=unwind");
     println!("cargo:rustc-link-search=native={}", out_dir);