RISCV relaxations (#408)

This PR enables RISC-V relaxations and changes to internal linkage for internal function and global symbols.

See also:
https://github.com/llvm/llvm-project/issues/167381#issuecomment-3513830043

Signed-off-by: xermicus <cyrill@parity.io>

CHANGELOG.md

@@ -6,6 +6,9 @@ This is a development pre-release.
 
 Supported `polkadot-sdk` rev: `2509.0.0`
 
+### Changed
+- Instruct the LLVM backend and linker to `--relax` (may lead to smaller contract code size).
+
 ## v0.5.0
 
 This is a development pre-release.

crates/integration/codesize.json

@@ -1,10 +1,10 @@
 {
-  "Baseline": 914,
-  "Computation": 2295,
-  "DivisionArithmetics": 14496,
-  "ERC20": 17482,
-  "Events": 1674,
-  "FibonacciIterative": 1490,
-  "Flipper": 2086,
-  "SHA1": 8158
+  "Baseline": 905,
+  "Computation": 2286,
+  "DivisionArithmetics": 14347,
+  "ERC20": 16929,
+  "Events": 1665,
+  "FibonacciIterative": 1447,
+  "Flipper": 2077,
+  "SHA1": 7721
 }

crates/linker/src/elf.rs

@@ -78,7 +78,7 @@ SECTIONS {
             "--error-limit=0",
             "--relocatable",
             "--emit-relocs",
-            "--no-relax",
+            "--relax",
             "--unique",
             "--gc-sections",
             self.linker_script_path.to_str().expect("should be utf8"),

crates/llvm-context/src/polkavm/context/global.rs

@@ -35,7 +35,7 @@ impl<'ctx> Global<'ctx> {
             .add_global(r#type, Some(address_space.into()), name);
         let global = Self { r#type, value };
 
-        global.value.set_linkage(inkwell::module::Linkage::External);
+        global.value.set_linkage(inkwell::module::Linkage::Internal);
         global
             .value
             .set_visibility(inkwell::GlobalVisibility::Default);

crates/llvm-context/src/polkavm/context/mod.rs

@@ -134,7 +134,7 @@ impl<'ctx> Context<'ctx> {
             module
                 .get_function(import)
                 .unwrap_or_else(|| panic!("{import} import should be declared"))
-                .set_linkage(inkwell::module::Linkage::External);
+                .set_linkage(inkwell::module::Linkage::Internal);
         }
     }
 

crates/llvm-context/src/target_machine/mod.rs

@@ -29,7 +29,7 @@ impl TargetMachine {
 
     /// LLVM target features.
     pub const VM_FEATURES: &'static str =
-        "+e,+m,+a,+c,+zbb,+auipc-addi-fusion,+ld-add-fusion,+lui-addi-fusion,+xtheadcondmov";
+        "+e,+m,+a,+c,+zbb,+auipc-addi-fusion,+ld-add-fusion,+lui-addi-fusion,+xtheadcondmov,+relax";
 
     /// A shortcut constructor.
     /// A separate instance for every optimization level is created.

crates/yul/src/parser/statement/function_definition.rs

@@ -215,7 +215,7 @@ impl PolkaVMWriteLLVM for FunctionDefinition {
             self.identifier.as_str(),
             function_type,
             self.result.len(),
-            Some(inkwell::module::Linkage::External),
+            Some(inkwell::module::Linkage::Internal),
             Some((self.location.line, self.location.column)),
             true,
         )?;