Use EBB offsets for encoding RISC-V branches.

Stop emitting EBB relocations. Use the offsets computed by
relax_branches() to encode the correct displacements immediately.

filetests/isa/riscv/binary32.cton

@@ -80,23 +80,40 @@ ebb0:
     ; Control Transfer Instructions
 
 ebb1:
-    ; beq
+    ; beq 0x000
-    br_icmp eq, v1, v2, ebb0            ; bin: Branch(ebb0) 01550063
+    br_icmp eq, v1, v2, ebb1            ; bin: 01550063
-    ; bne
+    ; bne 0xffc
-    br_icmp ne, v1, v2, ebb0            ; bin: Branch(ebb0) 01551063
+    br_icmp ne, v1, v2, ebb1            ; bin: ff551ee3
-    ; blt
+    ; blt 0xff8
-    br_icmp slt, v1, v2, ebb0           ; bin: Branch(ebb0) 01554063
+    br_icmp slt, v1, v2, ebb1           ; bin: ff554ce3
-    ; bge
+    ; bge 0xff4
-    br_icmp sge, v1, v2, ebb0           ; bin: Branch(ebb0) 01555063
+    br_icmp sge, v1, v2, ebb1           ; bin: ff555ae3
-    ; bltu
+    ; bltu 0xff0
-    br_icmp ult, v1, v2, ebb0           ; bin: Branch(ebb0) 01556063
+    br_icmp ult, v1, v2, ebb1           ; bin: ff5568e3
-    ; bgeu
+    ; bgeu 0xfec
-    br_icmp uge, v1, v2, ebb0           ; bin: Branch(ebb0) 01557063
+    br_icmp uge, v1, v2, ebb1           ; bin: ff5576e3
 
+    ; Forward branches.
+    ; beq 0x018
+    br_icmp eq, v2, v1, ebb2            ; bin: 00aa8c63
+    ; bne 0x014
+    br_icmp ne, v2, v1, ebb2            ; bin: 00aa9a63
+    ; blt 0x010
+    br_icmp slt, v2, v1, ebb2           ; bin: 00aac863
+    ; bge 0x00c
+    br_icmp sge, v2, v1, ebb2           ; bin: 00aad663
+    ; bltu 0x008
+    br_icmp ult, v2, v1, ebb2           ; bin: 00aae463
+    ; bgeu 0x004
+    br_icmp uge, v2, v1, ebb2           ; bin: 00aaf263
+
+    jump ebb2
+
+ebb2:
     ; beq x, %x0
-    brz v1, ebb0                        ; bin: Branch(ebb0) 00050063
+    brz v1, ebb2                        ; bin: 00050063
     ; bne x, %x0
-    brnz v1, ebb0                       ; bin: Branch(ebb0) 00051063
+    brnz v1, ebb2                       ; bin: fe051ee3
 
     return
 }

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

@@ -3,10 +3,12 @@
 use binemit::{CodeSink, Reloc, bad_encoding};
 use ir::{Function, Inst, InstructionData};
 use isa::RegUnit;
+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,
@@ -213,17 +215,17 @@ fn recipe_u<CS: CodeSink + ?Sized>(func: &Function, inst: Inst, sink: &mut CS) {
 ///   imm rs2 rs1 funct3 imm opcode
 ///    25  20  15     12   7      0
 ///
-/// The imm bits are not encoded by this function. They encode the relative distance to the
-/// destination block, handled by a relocation.
-///
 /// Encoding bits: `opcode[6:2] | (funct3 << 5)`
-fn put_sb<CS: CodeSink + ?Sized>(bits: u16, rs1: RegUnit, rs2: RegUnit, sink: &mut CS) {
+fn put_sb<CS: CodeSink + ?Sized>(bits: u16, imm: i64, rs1: RegUnit, rs2: RegUnit, sink: &mut CS) {
     let bits = bits as u32;
     let opcode5 = bits & 0x1f;
     let funct3 = (bits >> 5) & 0x7;
     let rs1 = rs1 as u32 & 0x1f;
     let rs2 = rs2 as u32 & 0x1f;
 
+    assert!(is_signed_int(imm, 13, 1), "SB out of range {:#x}", imm);
+    let imm = imm as u32;
+
     // 0-6: opcode
     let mut i = 0x3;
     i |= opcode5 << 2;
@@ -231,6 +233,12 @@ fn put_sb<CS: CodeSink + ?Sized>(bits: u16, rs1: RegUnit, rs2: RegUnit, sink: &m
     i |= rs1 << 15;
     i |= rs2 << 20;
 
+    // The displacement is completely hashed up.
+    i |= ((imm >> 11) & 0x1) << 7;
+    i |= ((imm >> 1) & 0xf) << 8;
+    i |= ((imm >> 5) & 0x3f) << 25;
+    i |= ((imm >> 12) & 0x1) << 31;
+
     sink.put4(i);
 }
 
@@ -240,9 +248,11 @@ fn recipe_sb<CS: CodeSink + ?Sized>(func: &Function, inst: Inst, sink: &mut CS)
                ref args,
                ..
            } = func.dfg[inst] {
+        let dest = func.offsets[destination] as i64;
+        let disp = dest - sink.offset() as i64;
         let args = &args.as_slice(&func.dfg.value_lists)[0..2];
-        sink.reloc_ebb(RelocKind::Branch.into(), destination);
         put_sb(func.encodings[inst].bits(),
+               disp,
                func.locations[args[0]].unwrap_reg(),
                func.locations[args[1]].unwrap_reg(),
                sink);
@@ -257,9 +267,11 @@ fn recipe_sbzero<CS: CodeSink + ?Sized>(func: &Function, inst: Inst, sink: &mut
                ref args,
                ..
            } = func.dfg[inst] {
+        let dest = func.offsets[destination] as i64;
+        let disp = dest - sink.offset() as i64;
         let args = &args.as_slice(&func.dfg.value_lists)[0..1];
-        sink.reloc_ebb(RelocKind::Branch.into(), destination);
         put_sb(func.encodings[inst].bits(),
+               disp,
                func.locations[args[0]].unwrap_reg(),
                0,
                sink);