Heed uext and sext annotations on RISC-V arguments.

Translate the small integer arguments to i32 or i64 with the appropriate
extend and ireduce instructions.

cranelift/filetests/isa/riscv/abi.cton

@@ -41,6 +41,13 @@ ebb0(v0: i64):
     return v0
 }
 
+function int_ext(i8, i8 sext, i8 uext) -> i8 {
+ebb0(v1: i8, v2: i8, v3: i8):
+; check: $ebb0($v1: i8, $(v2x=$VX): i32, $(v3x=$VX): i32):
+; check: ireduce.i8 $v2x
+; check: ireduce.i8 $v3x
+}
+
 function vector_split_args(i64x4) -> i64 {
 ebb0(v0: i64x4):
 ; check: $ebb0($(v0al=$VX): i32, $(v0ah=$VX): i32, $(v0bl=$VX): i32, $(v0bh=$VX): i32, $(v0cl=$VX): i32, $(v0ch=$VX): i32, $(v0dl=$VX): i32, $(v0dh=$VX): i32):

lib/cretonne/src/isa/riscv/abi.rs

@@ -6,13 +6,14 @@
 //! This doesn't support the soft-float ABI at the moment.
 
 use abi::{ArgAction, ValueConversion, ArgAssigner, legalize_args};
-use ir::{Signature, ArgumentType, ArgumentLoc};
+use ir::{Signature, Type, ArgumentType, ArgumentLoc, ArgumentExtension};
 use isa::riscv::registers::{GPR, FPR};
 use settings as shared_settings;
 
 struct Args {
     pointer_bits: u16,
     pointer_bytes: u32,
+    pointer_type: Type,
     regs: u32,
     offset: u32,
 }
@@ -22,6 +23,7 @@ impl Args {
         Args {
             pointer_bits: bits,
             pointer_bytes: bits as u32 / 8,
+            pointer_type: Type::int(bits).unwrap(),
             regs: 0,
             offset: 0,
         }
@@ -50,6 +52,19 @@ impl ArgAssigner for Args {
             return ArgAction::Convert(ValueConversion::IntSplit);
         }
 
+        // Small integers are extended to the size of a pointer register.
+        if ty.is_int() && ty.bits() < self.pointer_bits {
+            match arg.extension {
+                ArgumentExtension::None => {}
+                ArgumentExtension::Uext => {
+                    return ArgAction::Convert(ValueConversion::Uext(self.pointer_type))
+                }
+                ArgumentExtension::Sext => {
+                    return ArgAction::Convert(ValueConversion::Sext(self.pointer_type))
+                }
+            }
+        }
+
         if self.regs < 8 {
             // Assign to a register.
             let reg = if ty.is_float() {