Add RISC-V call instruction encodings.

Calls are jal with a fixed %x1 link register.

cranelift/filetests/isa/riscv/binary32.cton

@@ -3,6 +3,8 @@ test binemit
 isa riscv
 
 function RV32I() {
+    fn0 = function foo()
+
 ebb0:
     [-,%x10]            v1 = iconst.i32 1
     [-,%x21]            v2 = iconst.i32 2
@@ -75,11 +77,14 @@ ebb0:
     [-,%x7]     v140 = iconst.i32 0x12345000            ; bin: 123453b7
     [-,%x16]    v141 = iconst.i32 0xffffffff_fedcb000   ; bin: fedcb837
 
+    ; Control Transfer Instructions
+
+    ; jal %x1, fn0
+    call fn0()                                  ; bin: Call(fn0) 000000ef
+
     brz v1, ebb3
     fallthrough ebb1
 
-    ; Control Transfer Instructions
-
 ebb1:
     ; beq 0x000
     br_icmp eq v1, v2, ebb1             ; bin: 01550063

lib/cretonne/meta/isa/riscv/encodings.py

@@ -6,7 +6,8 @@ from base import instructions as base
 from base.immediates import intcc
 from .defs import RV32, RV64
 from .recipes import OPIMM, OPIMM32, OP, OP32, LUI, BRANCH, JALR, JAL
-from .recipes import R, Rshamt, Ricmp, I, Iicmp, Iret, U, UJ, SB, SBzero
+from .recipes import R, Rshamt, Ricmp, I, Iicmp, Iret
+from .recipes import U, UJ, UJcall, SB, SBzero
 from .settings import use_m
 from cdsl.ast import Var
 
@@ -84,6 +85,8 @@ RV64.enc(base.imul.i32, R, OP32(0b000, 0b0000001), isap=use_m)
 # Unconditional branches.
 RV32.enc(base.jump, UJ, JAL())
 RV64.enc(base.jump, UJ, JAL())
+RV32.enc(base.call, UJcall, JAL())
+RV64.enc(base.call, UJcall, JAL())
 
 # Conditional branches.
 for cond,           f3 in [

lib/cretonne/meta/isa/riscv/recipes.py

@@ -12,7 +12,7 @@ from __future__ import absolute_import
 from cdsl.isa import EncRecipe
 from cdsl.predicates import IsSignedInt
 from base.formats import Binary, BinaryImm, MultiAry, IntCompare, IntCompareImm
-from base.formats import UnaryImm, BranchIcmp, Branch, Jump
+from base.formats import UnaryImm, BranchIcmp, Branch, Jump, Call
 from .registers import GPR
 
 # The low 7 bits of a RISC-V instruction is the base opcode. All 32-bit
@@ -119,6 +119,7 @@ U = EncRecipe(
 
 # UJ-type unconditional branch instructions.
 UJ = EncRecipe('UJ', Jump, size=4, ins=(), outs=(), branch_range=(0, 21))
+UJcall = EncRecipe('UJcall', Call, size=4, ins=(), outs=())
 
 # SB-type branch instructions.
 # TODO: These instructions have a +/- 4 KB branch range. How to encode that

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

@@ -8,13 +8,12 @@ use predicates::is_signed_int;
 include!(concat!(env!("OUT_DIR"), "/binemit-riscv.rs"));
 
 /// RISC-V relocation kinds.
-#[allow(dead_code)]
 pub enum RelocKind {
-    /// A conditional (SB-type) branch to an EBB.
-    Branch,
+    /// A jal call to a function.
+    Call,
 }
 
-pub static RELOC_NAMES: [&'static str; 1] = ["Branch"];
+pub static RELOC_NAMES: [&'static str; 1] = ["Call"];
 
 impl Into<Reloc> for RelocKind {
     fn into(self) -> Reloc {
@@ -318,3 +317,13 @@ fn recipe_uj<CS: CodeSink + ?Sized>(func: &Function, inst: Inst, sink: &mut CS)
         panic!("Expected Jump format: {:?}", func.dfg[inst]);
     }
 }
+
+fn recipe_ujcall<CS: CodeSink + ?Sized>(func: &Function, inst: Inst, sink: &mut CS) {
+    if let InstructionData::Call { func_ref, .. } = func.dfg[inst] {
+        sink.reloc_func(RelocKind::Call.into(), func_ref);
+        // rd=%x1 is the standard link register.
+        put_uj(func.encodings[inst].bits(), 0, 1, sink);
+    } else {
+        panic!("Expected Call format: {:?}", func.dfg[inst]);
+    }
+}