More i8 legalizations (#1253)

* Legalize stack_{load,store}.i8, fixes #433
* Legalize select.i8, cc: #466
* Legalize brz.i8 and brnz.i8, cc: #1117

cranelift/filetests/filetests/isa/x86/brz-i8-run.clif

@@ -0,0 +1,34 @@
+test run
+target x86_64
+
+function u0:0() -> b1 {
+ebb0:
+    v0 = iconst.i8 0
+    brz v0, ebb1
+    jump ebb2
+
+ebb1:
+    v1 = bconst.b1 true
+    return v1
+
+ebb2:
+    v2 = bconst.b1 false
+    return v2
+}
+; run
+
+function u0:1() -> b1 {
+ebb0:
+    v0 = iconst.i8 0
+    brnz v0, ebb1
+    jump ebb2
+
+ebb1:
+    v1 = bconst.b1 false
+    return v1
+
+ebb2:
+    v2 = bconst.b1 true
+    return v2
+}
+; run

cranelift/filetests/filetests/isa/x86/brz-i8.clif

@@ -0,0 +1,38 @@
+test compile
+target x86_64
+
+function u0:0() -> b1 {
+ebb0:
+    v0 = iconst.i8 0
+    ; check: v0 = iconst.i8 0
+    brz v0, ebb1
+    ; nextln: v3 = uextend.i32 v0
+    ; nextln: brz v3, ebb1
+    jump ebb2
+
+ebb1:
+    v1 = bconst.b1 true
+    return v1
+
+ebb2:
+    v2 = bconst.b1 false
+    return v2
+}
+
+function u0:1() -> b1 {
+ebb0:
+    v0 = iconst.i8 0
+    ; check: v0 = iconst.i8 0
+    brnz v0, ebb1
+    ; nextln: v3 = uextend.i32 v0
+    ; nextln: brnz v3, ebb1
+    jump ebb2
+
+ebb1:
+    v1 = bconst.b1 false
+    return v1
+
+ebb2:
+    v2 = bconst.b1 true
+    return v2
+}

cranelift/filetests/filetests/isa/x86/select-i8.clif

@@ -0,0 +1,8 @@
+test compile
+target x86_64
+
+function u0:0(b1, i8, i8) -> i8 {
+ebb0(v0: b1, v1: i8, v2: i8):
+    v3 = select v0, v1, v2
+    return v3
+}

cranelift/filetests/filetests/isa/x86/stack-load-store8.clif

@@ -0,0 +1,19 @@
+test compile
+target x86_64
+
+function u0:0(i8) -> i8 {
+    ss0 = explicit_slot 1
+
+ebb0(v0: i8):
+    stack_store v0, ss0
+    ; check: v2 = stack_addr.i64 ss0
+    ; nextln: v3 = uextend.i32 v0
+    ; nextln: istore8 notrap aligned v3, v2
+
+    v1 = stack_load.i8 ss0
+    ; check: v4 = stack_addr.i64 ss0
+    ; nextln: v5 = uload8.i32 notrap aligned v4
+    ; nextln: v1 = ireduce.i8 v5
+
+    return v1
+}