riscv64: Use labels for branches whenever possible (#6955)

* riscv64: Use label based jump in Icmp

* riscv64: Use labels in LoadExtData

* riscv64: Use labels in BrTable

* riscv64: Delete BranchTarget::offset

* riscv64: Enable default extensions

cranelift/codegen/meta/src/isa/riscv64.rs

@@ -28,12 +28,23 @@ macro_rules! define_zvl_ext {
 pub(crate) fn define() -> TargetIsa {
     let mut setting = SettingGroupBuilder::new("riscv64");
 
-    let _has_m = setting.add_bool("has_m", "has extension M?", "", false);
-    let _has_a = setting.add_bool("has_a", "has extension A?", "", false);
-    let _has_f = setting.add_bool("has_f", "has extension F?", "", false);
-    let _has_d = setting.add_bool("has_d", "has extension D?", "", false);
+    // We target a minimum of riscv64gc. That means that we have the following extensions by default:
+    //
+    // * M (integer multiplication and division)
+    // * A (atomic instructions)
+    // * F (single-precision floating point)
+    // * D (double-precision floating point)
+    // * C (compressed instructions)
+    // * Zicsr (control and status register instructions)
+    // * Zifencei (instruction-fetch fence)
+
+    let _has_m = setting.add_bool("has_m", "has extension M?", "", true);
+    let _has_a = setting.add_bool("has_a", "has extension A?", "", true);
+    let _has_f = setting.add_bool("has_f", "has extension F?", "", true);
+    let _has_d = setting.add_bool("has_d", "has extension D?", "", true);
     let _has_v = setting.add_bool("has_v", "has extension V?", "", false);
-    let _has_c = setting.add_bool("has_c", "has extension C?", "", false);
+    let _has_c = setting.add_bool("has_c", "has extension C?", "", true);
+
     let _has_zbkb = setting.add_bool(
         "has_zbkb",
         "has extension zbkb?",
@@ -69,13 +80,13 @@ pub(crate) fn define() -> TargetIsa {
         "has_zicsr",
         "has extension zicsr?",
         "Zicsr: Control and Status Register (CSR) Instructions",
-        false,
+        true,
     );
     let _has_zifencei = setting.add_bool(
         "has_zifencei",
         "has extension zifencei?",
         "Zifencei: Instruction-Fetch Fence",
-        false,
+        true,
     );
 
     // Zvl*: Minimum Vector Length Standard Extensions

cranelift/codegen/src/isa/riscv64/inst/emit.rs

@@ -1042,6 +1042,8 @@ impl MachInstEmit for Inst {
                 let tmp2 = allocs.next_writable(tmp2);
                 let ext_index = writable_spilltmp_reg();
 
+                let label_compute_target = sink.get_label();
+
                 // The default target is passed in as the 0th element of `targets`
                 // separate it here for clarity.
                 let default_target = targets[0];
@@ -1094,7 +1096,7 @@ impl MachInstEmit for Inst {
                     .iter()
                     .for_each(|i| i.emit(&[], sink, emit_info, state));
                 Inst::CondBr {
-                    taken: BranchTarget::offset(Inst::INSTRUCTION_SIZE * 3),
+                    taken: BranchTarget::Label(label_compute_target),
                     not_taken: BranchTarget::zero(),
                     kind: IntegerCompare {
                         kind: IntCC::UnsignedLessThan,
@@ -1114,6 +1116,7 @@ impl MachInstEmit for Inst {
 
                 // Compute the jump table offset.
                 // We need to emit a PC relative offset,
+                sink.bind_label(label_compute_target, &mut state.ctrl_plane);
 
                 // Get the current PC.
                 Inst::Auipc {
@@ -1363,6 +1366,8 @@ impl MachInstEmit for Inst {
                 let rd = allocs.next_writable(rd);
                 let label_true = sink.get_label();
                 let label_false = sink.get_label();
+                let label_end = sink.get_label();
+
                 Inst::lower_br_icmp(
                     cc,
                     a,
@@ -1377,11 +1382,12 @@ impl MachInstEmit for Inst {
                 sink.bind_label(label_true, &mut state.ctrl_plane);
                 Inst::load_imm12(rd, Imm12::TRUE).emit(&[], sink, emit_info, state);
                 Inst::Jal {
-                    dest: BranchTarget::offset(Inst::INSTRUCTION_SIZE * 2),
+                    dest: BranchTarget::Label(label_end),
                 }
                 .emit(&[], sink, emit_info, state);
                 sink.bind_label(label_false, &mut state.ctrl_plane);
                 Inst::load_imm12(rd, Imm12::FALSE).emit(&[], sink, emit_info, state);
+                sink.bind_label(label_end, &mut state.ctrl_plane);
             }
             &Inst::AtomicCas {
                 offset,
@@ -1958,33 +1964,30 @@ impl MachInstEmit for Inst {
                 offset,
             } => {
                 let rd = allocs.next_writable(rd);
-                // get the current pc.
-                Inst::Auipc {
-                    rd: rd,
-                    imm: Imm20::from_bits(0),
-                }
-                .emit(&[], sink, emit_info, state);
-                // load the value.
+
+                let label_data = sink.get_label();
+                let label_end = sink.get_label();
+
+                // Load the value from a label
                 Inst::Load {
-                    rd: rd,
+                    rd,
                     op: LoadOP::Ld,
                     flags: MemFlags::trusted(),
-                    from: AMode::RegOffset(
-                        rd.to_reg(),
-                        12, // auipc load and jal.
-                        I64,
-                    ),
+                    from: AMode::Label(label_data),
                 }
                 .emit(&[], sink, emit_info, state);
-                // jump over.
+
+                // Jump over the data
                 Inst::Jal {
-                    // jal and abs8 size for 12.
-                    dest: BranchTarget::offset(12),
+                    dest: BranchTarget::Label(label_end),
                 }
                 .emit(&[], sink, emit_info, state);
 
+                sink.bind_label(label_data, &mut state.ctrl_plane);
                 sink.add_reloc(Reloc::Abs8, name.as_ref(), offset);
                 sink.put8(0);
+
+                sink.bind_label(label_end, &mut state.ctrl_plane);
             }
             &Inst::TrapIfC {
                 rs1,

cranelift/codegen/src/isa/riscv64/inst/mod.rs

@@ -127,10 +127,7 @@ impl BranchTarget {
     pub(crate) fn zero() -> Self {
         Self::ResolvedOffset(0)
     }
-    #[inline]
-    pub(crate) fn offset(off: i32) -> Self {
-        Self::ResolvedOffset(off)
-    }
+
     #[inline]
     pub(crate) fn is_zero(self) -> bool {
         match self {
@@ -138,6 +135,7 @@ impl BranchTarget {
             BranchTarget::ResolvedOffset(off) => off == 0,
         }
     }
+
     #[inline]
     pub(crate) fn as_offset(self) -> Option<i32> {
         match self {