Add tests for branch order and branch comparison folding.

cranelift/filetests/filetests/simple_preopt/branch.clif

@@ -16,8 +16,8 @@ ebb2:
 ; sameln: function %brif_to_brz_fold
 ; nextln: ebb0(v0: i32):
 ; nextln:     v1 = ifcmp_imm v0, 0
-; nextln:     brz v0, ebb1
-; nextln:     jump ebb2
+; nextln:     brnz v0, ebb2
+; nextln:     fallthrough ebb1
 ; nextln: 
 ; nextln: ebb1:
 ; nextln:     v2 = iconst.i32 1
@@ -27,3 +27,57 @@ ebb2:
 ; nextln:     v3 = iconst.i32 2
 ; nextln:     return v3
 ; nextln: }
+
+function %brif_inversion(i32) -> i32 {
+ebb0(v0: i32):
+    v1 = ifcmp_imm v0, 42
+    brif ugt v1, ebb1
+    jump ebb2
+ebb1:
+    v2 = iconst.i32 1
+    return v2
+ebb2:
+    v3 = iconst.i32 2
+    return v3
+}
+; sameln: function %brif_inversion
+; nextln: ebb0(v0: i32):
+; nextln:     v1 = ifcmp_imm v0, 42
+; nextln:     brif ule v1, ebb2
+; nextln:     fallthrough ebb1
+; nextln: 
+; nextln: ebb1:
+; nextln:     v2 = iconst.i32 1
+; nextln:     return v2
+; nextln: 
+; nextln: ebb2:
+; nextln:     v3 = iconst.i32 2
+; nextln:     return v3
+; nextln: }
+
+function %brff_inversion(f32, f32) -> i32 {
+ebb0(v0: f32, v1: f32):
+    v2 = ffcmp v0, v1
+    brff gt v2, ebb1
+    jump ebb2
+ebb1:
+    v3 = iconst.i32 1
+    return v3
+ebb2:
+    v4 = iconst.i32 2
+    return v4
+}
+; sameln: function %brff_inversion
+; nextln: ebb0(v0: f32, v1: f32):
+; nextln:     v2 = ffcmp v0, v1
+; nextln:     brff ule v2, 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: }

cranelift/filetests/filetests/simple_preopt/simplify.clif

@@ -63,8 +63,8 @@ ebb2:
 ; nextln:    v1 = bint.i32 v3
 ; nextln:    v2 = select v3, v1, v1
 ; nextln:    trapz v3, user0
-; nextln:    brz v3, ebb1
-; nextln:    jump ebb2
+; nextln:    brnz v3, ebb2
+; nextln:    fallthrough ebb1
 
 function %irsub_imm(i32) -> i32 {
 ebb0(v0: i32):