Legalize br_icmp (#449)

* Legalize br_icmp

cranelift/filetests/isa/x86/legalize-br-icmp.clif

@@ -0,0 +1,46 @@
+test legalizer
+
+target x86_64
+
+function %br_icmp(i64) fast {
+ebb0(v0: i64):
+    v1 = iconst.i64 0
+    br_icmp eq v0, v1, ebb1
+    jump ebb1
+
+ebb1:
+    return
+}
+
+; sameln: function %br_icmp(i64 [%rdi]) fast {
+; nextln:                                 ebb0(v0: i64):
+; nextln: [RexOp1pu_id#b8]                    v1 = iconst.i64 0
+; nextln: [RexOp1icscc#8039]                  v2 = icmp eq v0, v1
+; nextln: [RexOp1t8jccb#75]                   brnz v2, ebb1
+; nextln: [RexOp1jmpb#eb]                     jump ebb1
+; nextln: 
+; nextln:                                 ebb1:
+; nextln: [Op1ret#c3]                         return
+; nextln: }
+
+
+function %br_icmp_ebb_args(i64) fast {
+ebb0(v0: i64):
+    v1 = iconst.i64 0
+    br_icmp eq v0, v1, ebb1(v0)
+    jump ebb1(v0)
+
+ebb1(v2: i64):
+    return
+}
+
+; sameln: function %br_icmp_ebb_args(i64 [%rdi]) fast {
+; nextln:                                 ebb0(v0: i64):
+; nextln: [RexOp1pu_id#b8]                    v1 = iconst.i64 0
+; nextln: [RexOp1icscc#8039]                  v3 = icmp eq v0, v1
+; nextln: [RexOp1t8jccb#75]                   brnz v3, ebb1(v0)
+; nextln: [RexOp1jmpb#eb]                     jump ebb1(v0)
+; nextln: 
+; nextln:                                 ebb1(v2: i64):
+; nextln: [Op1ret#c3]                         return
+; nextln: }

lib/codegen/meta-python/base/legalize.py

@@ -407,6 +407,7 @@ for ty,             minus_zero in [
                 a << bor(a1, a2)
             ))
 
+expand.custom_legalize(insts.br_icmp, 'expand_br_icmp')
 
 # Expansions using CPU flags.
 

lib/codegen/src/legalizer/mod.rs

@@ -244,6 +244,40 @@ fn expand_select(
     cfg.recompute_ebb(pos.func, old_ebb);
 }
 
+fn expand_br_icmp(
+    inst: ir::Inst,
+    func: &mut ir::Function,
+    cfg: &mut ControlFlowGraph,
+    _isa: &TargetIsa,
+) {
+    let (cond, a, b, destination, ebb_args) = match func.dfg[inst] {
+        ir::InstructionData::BranchIcmp {
+            cond,
+            destination,
+            ref args,
+            ..
+        } => (
+            cond,
+            args.get(0, &func.dfg.value_lists).unwrap(),
+            args.get(1, &func.dfg.value_lists).unwrap(),
+            destination,
+            args.as_slice(&func.dfg.value_lists)[2..].to_vec(),
+        ),
+        _ => panic!("Expected br_icmp {}", func.dfg.display_inst(inst, None)),
+    };
+
+    let old_ebb = func.layout.pp_ebb(inst);
+    func.dfg.clear_results(inst);
+
+    let icmp_res = func.dfg.replace(inst).icmp(cond, a, b);
+    let mut pos = FuncCursor::new(func).after_inst(inst);
+    pos.use_srcloc(inst);
+    pos.ins().brnz(icmp_res, destination, &ebb_args);
+
+    cfg.recompute_ebb(pos.func, destination);
+    cfg.recompute_ebb(pos.func, old_ebb);
+}
+
 /// Expand illegal `f32const` and `f64const` instructions.
 fn expand_fconst(
     inst: ir::Inst,