Auto merge of #117465 - paulmenage:small-data-limit, r=compiler-errors

Add -Z small-data-threshold

This flag allows specifying the threshold size above which LLVM should not consider placing small objects in a `.sdata` or `.sbss` section.

Support is indicated in the target options via the
small-data-threshold-support target option, which can indicate either an
LLVM argument or an LLVM module flag.  To avoid duplicate specifications
in a large number of targets, the default value for support is
DefaultForArch, which is translated to a concrete value according to the
target's architecture.

1 files changed, 13 insertions, 1 deletions

diff --git a/compiler/rustc_codegen_llvm/src/llvm_util.rs b/compiler/rustc_codegen_llvm/src/llvm_util.rs
index 6e4ddbb6f3b..29afe6f6bfc 100644
--- a/compiler/rustc_codegen_llvm/src/llvm_util.rs
+++ b/compiler/rustc_codegen_llvm/src/llvm_util.rs
@@ -14,7 +14,7 @@ use rustc_middle::bug;
 use rustc_session::config::{PrintKind, PrintRequest};
 use rustc_session::Session;
 use rustc_span::symbol::Symbol;
-use rustc_target::spec::{MergeFunctions, PanicStrategy};
+use rustc_target::spec::{MergeFunctions, PanicStrategy, SmallDataThresholdSupport};
 use rustc_target::target_features::{RUSTC_SPECIAL_FEATURES, RUSTC_SPECIFIC_FEATURES};
 
 use crate::back::write::create_informational_target_machine;
@@ -125,6 +125,18 @@ unsafe fn configure_llvm(sess: &Session) {
         for arg in sess_args {
             add(&(*arg), true);
         }
+
+        match (
+            sess.opts.unstable_opts.small_data_threshold,
+            sess.target.small_data_threshold_support(),
+        ) {
+            // Set up the small-data optimization limit for architectures that use
+            // an LLVM argument to control this.
+            (Some(threshold), SmallDataThresholdSupport::LlvmArg(arg)) => {
+                add(&format!("--{arg}={threshold}"), false)
+            }
+            _ => (),
+        };
     }
 
     if sess.opts.unstable_opts.llvm_time_trace {