Merge pull request #2363 from cfallin/extend-only-if-abi

Do value-extensions at ABI boundaries only when ABI requires it.

cranelift/codegen/src/isa/aarch64/abi.rs

@@ -728,6 +728,19 @@ impl ABIMachineSpec for AArch64MachineDeps {
         }
         caller_saved
     }
+
+    fn get_ext_mode(
+        call_conv: isa::CallConv,
+        specified: ir::ArgumentExtension,
+    ) -> ir::ArgumentExtension {
+        if call_conv.extends_baldrdash() {
+            // Baldrdash (SpiderMonkey) always extends args and return values to the full register.
+            specified
+        } else {
+            // No other supported ABI on AArch64 does so.
+            ir::ArgumentExtension::None
+        }
+    }
 }
 
 /// Is this type supposed to be seen on this machine? E.g. references of the

cranelift/codegen/src/isa/arm32/abi.rs

@@ -445,6 +445,13 @@ impl ABIMachineSpec for Arm32MachineDeps {
         }
         caller_saved
     }
+
+    fn get_ext_mode(
+        _call_conv: isa::CallConv,
+        specified: ir::ArgumentExtension,
+    ) -> ir::ArgumentExtension {
+        specified
+    }
 }
 
 fn is_callee_save(r: RealReg) -> bool {

cranelift/codegen/src/isa/x64/abi.rs

@@ -591,6 +591,19 @@ impl ABIMachineSpec for X64ABIMachineSpec {
 
         caller_saved
     }
+
+    fn get_ext_mode(
+        call_conv: isa::CallConv,
+        specified: ir::ArgumentExtension,
+    ) -> ir::ArgumentExtension {
+        if call_conv.extends_baldrdash() {
+            // Baldrdash (SpiderMonkey) always extends args and return values to the full register.
+            specified
+        } else {
+            // No other supported ABI on x64 does so.
+            ir::ArgumentExtension::None
+        }
+    }
 }
 
 impl From<StackAMode> for SyntheticAmode {

cranelift/codegen/src/isa/x86/abi.rs

@@ -144,8 +144,13 @@ impl ArgAssigner for Args {
             return ValueConversion::VectorSplit.into();
         }
 
-        // Small integers are extended to the size of a pointer register.
-        if ty.is_int() && ty.bits() < u16::from(self.pointer_bits) {
+        // Small integers are extended to the size of a pointer register, but
+        // only in ABIs that require this. The Baldrdash (SpiderMonkey) ABI
+        // does, but our other supported ABIs on x86 do not.
+        if ty.is_int()
+            && ty.bits() < u16::from(self.pointer_bits)
+            && self.call_conv.extends_baldrdash()
+        {
             match arg.extension {
                 ArgumentExtension::None => {}
                 ArgumentExtension::Uext => return ValueConversion::Uext(self.pointer_type).into(),