Add the br_icmp instruction.

This instruction behaves like icmp fused with brnz, and it can be used
to represent fused compare+branch instruction on Intel when optimizing
for macro-op fusion.

RISC-V provides compare-and-branch instructions directly, and it is
needed there too.

docs/langref.rst

@@ -321,6 +321,7 @@ instruction in the EBB.
 .. autoinst:: jump
 .. autoinst:: brz
 .. autoinst:: brnz
+.. autoinst:: br_icmp
 .. autoinst:: br_table
 
 .. inst:: JT = jump_table EBB0, EBB1, ..., EBBn

filetests/parser/tiny.cton

@@ -56,6 +56,7 @@ ebb0(vx0: i32, vx1: i32):
     v1 = icmp ult, vx0, vx1
     v2 = icmp_imm sge, vx0, -12
     v3 = irsub_imm vx1, 45
+    br_icmp eq, vx0, vx1, ebb0(vx1, vx0)
 }
 ; sameln: function icmp(i32, i32) {
 ; nextln: ebb0(vx0: i32, vx1: i32):
@@ -63,6 +64,7 @@ ebb0(vx0: i32, vx1: i32):
 ; nextln:     v1 = icmp ult, vx0, vx1
 ; nextln:     v2 = icmp_imm sge, vx0, -12
 ; nextln:     v3 = irsub_imm vx1, 45
+; nextln:     br_icmp eq, vx0, vx1, ebb0(vx1, vx0)
 ; nextln: }
 
 ; Floating condition codes.

lib/cretonne/meta/base/formats.py

@@ -43,6 +43,7 @@ FloatCompare = InstructionFormat(floatcc, VALUE, VALUE)
 
 Jump = InstructionFormat(ebb, VARIABLE_ARGS)
 Branch = InstructionFormat(VALUE, ebb, VARIABLE_ARGS)
+BranchIcmp = InstructionFormat(intcc, VALUE, VALUE, ebb, VARIABLE_ARGS)
 BranchTable = InstructionFormat(VALUE, jump_table)
 
 Call = InstructionFormat(

lib/cretonne/meta/base/instructions.py

@@ -33,6 +33,9 @@ Any = TypeVar(
 # Control flow
 #
 c = Operand('c', Testable, doc='Controlling value to test')
+Cond = Operand('Cond', intcc)
+x = Operand('x', iB)
+y = Operand('y', iB)
 EBB = Operand('EBB', entities.ebb, doc='Destination extended basic block')
 args = Operand('args', VARIABLE_ARGS, doc='EBB arguments')
 
@@ -64,6 +67,26 @@ brnz = Instruction(
         """,
         ins=(c, EBB, args), is_branch=True)
 
+br_icmp = Instruction(
+        'br_icmp', r"""
+        Compare scalar integers and branch.
+
+        Compare ``x`` and ``y`` in the same way as the :inst:`icmp` instruction
+        and take the branch if the condition is true::
+
+            br_icmp ugt v1, v2, ebb4(v5, v6)
+
+        is semantically equivalent to::
+
+            v10 = icmp ugt, v1, v2
+            brnz v10, ebb4(v5, v6)
+
+        Some RISC architectures like MIPS and RISC-V provide instructions that
+        implement all or some of the condition codes. The instruction can also
+        be used to represent *macro-op fusion* on architectures like Intel's.
+        """,
+        ins=(Cond, x, y, EBB, args), is_branch=True)
+
 x = Operand('x', iB, doc='index into jump table')
 JT = Operand('JT', entities.jump_table)
 br_table = Instruction(

lib/cretonne/src/ir/instructions.rs

@@ -200,6 +200,13 @@ pub enum InstructionData {
         destination: Ebb,
         args: ValueList,
     },
+    BranchIcmp {
+        opcode: Opcode,
+        ty: Type,
+        cond: IntCC,
+        destination: Ebb,
+        args: ValueList,
+    },
     BranchTable {
         opcode: Opcode,
         ty: Type,
@@ -303,6 +310,9 @@ impl InstructionData {
             &InstructionData::Branch { destination, ref args, .. } => {
                 BranchInfo::SingleDest(destination, &args.as_slice(pool)[1..])
             }
+            &InstructionData::BranchIcmp { destination, ref args, .. } => {
+                BranchInfo::SingleDest(destination, &args.as_slice(pool)[2..])
+            }
             &InstructionData::BranchTable { table, .. } => BranchInfo::Table(table),
             _ => BranchInfo::NotABranch,
         }

lib/cretonne/src/verifier.rs

@@ -218,11 +218,9 @@ impl<'a> Verifier<'a> {
             &MultiAry { ref args, .. } => {
                 self.verify_value_list(inst, args)?;
             }
-            &Jump { destination, ref args, .. } => {
-                self.verify_ebb(inst, destination)?;
-                self.verify_value_list(inst, args)?;
-            }
-            &Branch { destination, ref args, .. } => {
+            &Jump { destination, ref args, .. } |
+            &Branch { destination, ref args, .. } |
+            &BranchIcmp { destination, ref args, .. } => {
                 self.verify_ebb(inst, destination)?;
                 self.verify_value_list(inst, args)?;
             }

lib/cretonne/src/write.rs

@@ -274,15 +274,19 @@ pub fn write_operands(w: &mut Write, dfg: &DataFlowGraph, inst: Inst) -> Result
         }
         Branch { destination, ref args, .. } => {
             let args = args.as_slice(pool);
-            if args.len() == 1 {
-                write!(w, " {}, {}", args[0], destination)
-            } else {
-                write!(w,
-                       " {}, {}({})",
-                       args[0],
-                       destination,
-                       DisplayValues(&args[1..]))
+            write!(w, " {}, {}", args[0], destination)?;
+            if args.len() > 1 {
+                write!(w, "({})", DisplayValues(&args[1..]))?;
             }
+            Ok(())
+        }
+        BranchIcmp { cond, destination, ref args, .. } => {
+            let args = args.as_slice(pool);
+            write!(w, " {}, {}, {}, {}", cond, args[0], args[1], destination)?;
+            if args.len() > 2 {
+                write!(w, "({})", DisplayValues(&args[2..]))?;
+            }
+            Ok(())
         }
         BranchTable { arg, table, .. } => write!(w, " {}, {}", arg, table),
         Call { func_ref, ref args, .. } => {

lib/reader/src/parser.rs

@@ -241,20 +241,14 @@ impl<'a> Context<'a> {
                         self.map.rewrite_values(args.as_mut_slice(value_lists), loc)?;
                     }
 
-                    InstructionData::Jump { ref mut destination, ref mut args, .. } => {
+                    InstructionData::Jump { ref mut destination, ref mut args, .. } |
+                    InstructionData::Branch { ref mut destination, ref mut args, .. } |
+                    InstructionData::BranchIcmp { ref mut destination, ref mut args, .. } => {
                         self.map.rewrite_ebb(destination, loc)?;
                         self.map.rewrite_values(args.as_mut_slice(value_lists), loc)?;
                     }
 
-                    InstructionData::Branch { ref mut destination, ref mut args, .. } => {
-                        self.map.rewrite_ebb(destination, loc)?;
-                        self.map.rewrite_values(args.as_mut_slice(value_lists), loc)?;
-                    }
-
-                    InstructionData::Call { ref mut args, .. } => {
-                        self.map.rewrite_values(args.as_mut_slice(value_lists), loc)?;
-                    }
-
+                    InstructionData::Call { ref mut args, .. } |
                     InstructionData::IndirectCall { ref mut args, .. } => {
                         self.map.rewrite_values(args.as_mut_slice(value_lists), loc)?;
                     }
@@ -1521,6 +1515,23 @@ impl<'a> Parser<'a> {
                     args: args.into_value_list(&[ctrl_arg], &mut ctx.function.dfg.value_lists),
                 }
             }
+            InstructionFormat::BranchIcmp => {
+                let cond = self.match_enum("expected intcc condition code")?;
+                self.match_token(Token::Comma, "expected ',' between operands")?;
+                let lhs = self.match_value("expected SSA value first operand")?;
+                self.match_token(Token::Comma, "expected ',' between operands")?;
+                let rhs = self.match_value("expected SSA value second operand")?;
+                self.match_token(Token::Comma, "expected ',' between operands")?;
+                let ebb_num = self.match_ebb("expected branch destination EBB")?;
+                let args = self.parse_opt_value_list()?;
+                InstructionData::BranchIcmp {
+                    opcode: opcode,
+                    ty: VOID,
+                    cond: cond,
+                    destination: ebb_num,
+                    args: args.into_value_list(&[lhs, rhs], &mut ctx.function.dfg.value_lists),
+                }
+            }
             InstructionFormat::InsertLane => {
                 let lhs = self.match_value("expected SSA value first operand")?;
                 self.match_token(Token::Comma, "expected ',' between operands")?;