Switch ifcmp+brif folding to be icmp+brz folding, which is what frontends actually produce.

cranelift/codegen/src/simple_preopt.rs

@@ -556,9 +556,8 @@ enum BranchOptKind {
 
 fn branch_opt(pos: &mut FuncCursor, inst: Inst) {
     let info = match pos.func.dfg[inst] {
-        InstructionData::BranchInt {
+        InstructionData::Branch {
-            opcode: Opcode::Brif,
+            opcode,
-            cond: br_cond,
             destination,
             ref args,
         } => {
@@ -566,6 +565,7 @@ fn branch_opt(pos: &mut FuncCursor, inst: Inst) {
                 let args = pos.func.dfg.inst_args(inst);
                 args[0]
             };
+
             let iconst_inst =
                 if let ValueDef::Result(iconst_inst, _) = pos.func.dfg.value_def(first_arg) {
                     iconst_inst
@@ -573,10 +573,11 @@ fn branch_opt(pos: &mut FuncCursor, inst: Inst) {
                     return;
                 };
 
-            if let InstructionData::BinaryImm {
+            if let InstructionData::IntCompareImm {
-                opcode: Opcode::IfcmpImm,
+                opcode: Opcode::IcmpImm,
-                imm: cmp_imm,
                 arg: cmp_arg,
+                cond: cmp_cond,
+                imm: cmp_imm,
             } = pos.func.dfg[iconst_inst]
             {
                 let cmp_imm: i64 = cmp_imm.into();
@@ -584,9 +585,17 @@ fn branch_opt(pos: &mut FuncCursor, inst: Inst) {
                     return;
                 }
 
-                let kind = match br_cond {
+                // icmp_imm returns non-zero when the comparison is true. So, if
-                    IntCC::NotEqual => BranchOptKind::NotEqualZero,
+                // we're branching on zero, we need to invert the condition.
+                let cond = match opcode {
+                    Opcode::Brz => cmp_cond.inverse(),
+                    Opcode::Brnz => cmp_cond,
+                    _ => return,
+                };
+
+                let kind = match cond {
                     IntCC::Equal => BranchOptKind::EqualZero,
+                    IntCC::NotEqual => BranchOptKind::NotEqualZero,
                     _ => return,
                 };
 

cranelift/filetests/filetests/simple_preopt/branch.clif

@@ -1,31 +1,58 @@
 test simple_preopt
 target x86_64
 
-function %brif_to_brz_fold(i32) -> i32 {
+function %icmp_to_brz_fold(i32) -> i32 {
 ebb0(v0: i32):
-    v1 = ifcmp_imm v0, 0
+    v1 = icmp_imm eq v0, 0
-    brif eq v1, ebb1
+    brnz v1, ebb1
     jump ebb2
 ebb1:
-    v2 = iconst.i32 1
+    v3 = iconst.i32 1
-    return v2
-ebb2:
-    v3 = iconst.i32 2
     return v3
+ebb2:
+    v4 = iconst.i32 2
+    return v4
 }
-; sameln: function %brif_to_brz_fold
+; sameln: function %icmp_to_brz_fold
 ; nextln: ebb0(v0: i32):
-; nextln:     v1 = ifcmp_imm v0, 0
+; nextln:     v1 = icmp_imm eq v0, 0
 ; nextln:     brnz v0, ebb2
 ; nextln:     fallthrough ebb1
 ; nextln: 
 ; nextln: ebb1:
-; nextln:     v2 = iconst.i32 1
+; nextln:     v3 = iconst.i32 1
-; nextln:     return v2
+; nextln:     return v3
 ; nextln: 
 ; nextln: ebb2:
-; nextln:     v3 = iconst.i32 2
+; nextln:     v4 = iconst.i32 2
+; nextln:     return v4
+; nextln: }
+
+function %icmp_to_brz_inverted_fold(i32) -> i32 {
+ebb0(v0: i32):
+    v1 = icmp_imm ne v0, 0
+    brz v1, ebb1
+    jump ebb2
+ebb1:
+    v3 = iconst.i32 1
+    return v3
+ebb2:
+    v4 = iconst.i32 2
+    return v4
+}
+; sameln: function %icmp_to_brz_inve
+; nextln: ebb0(v0: i32):
+; nextln:     v1 = icmp_imm ne v0, 0
+; nextln:     brnz v0, ebb2
+; nextln:     fallthrough ebb1
+; nextln: 
+; nextln: ebb1:
+; nextln:     v3 = iconst.i32 1
 ; nextln:     return v3
+; nextln: 
+; nextln: ebb2:
+; nextln:     v4 = iconst.i32 2
+; nextln:     return v4
 ; nextln: }
 
 function %brif_inversion(i32) -> i32 {