Revert "Revert "Use ICF (identical code folding) for building rustc""

src/bootstrap/compile.rs

@@ -651,6 +651,12 @@ impl Step for Rustc {
  panic!("Cannot use and generate PGO profiles at the same time");
  }
 
+ // With LLD, we can use ICF (identical code folding) to reduce the executable size
+ // of librustc_driver/rustc and to improve i-cache utilization.
+ if builder.config.use_lld {
+ cargo.rustflag("-Clink-args=-Wl,--icf=all");
+ }
+
  let is_collecting = if let Some(path) = &builder.config.rust_profile_generate {
  if compiler.stage == 1 {
  cargo.rustflag(&format!("-Cprofile-generate={}", path));

src/ci/docker/host-x86_64/dist-x86_64-linux/Dockerfile

@@ -122,7 +122,8 @@ ENV RUST_CONFIGURE_ARGS \
  --set target.x86_64-unknown-linux-gnu.ranlib=/rustroot/bin/llvm-ranlib \
  --set llvm.thin-lto=true \
  --set llvm.ninja=false \
- --set rust.jemalloc
+ --set rust.jemalloc \
+ --set rust.use-lld=true
 ENV SCRIPT ../src/ci/pgo.sh python3 ../x.py dist \
  --host $HOSTS --target $HOSTS \
  --include-default-paths \

src/ci/pgo.sh

@@ -195,3 +195,7 @@ rm -r $BUILD_ARTIFACTS/llvm $BUILD_ARTIFACTS/lld
 $@ \
  --rust-profile-use=${RUSTC_PROFILE_MERGED_FILE} \
  --llvm-profile-use=${LLVM_PROFILE_MERGED_FILE}
+
+echo "Rustc binary size"
+ls -la ./build/$PGO_HOST/stage2/bin
+ls -la ./build/$PGO_HOST/stage2/lib