Legalize [su]extend.i64 to iconst/sshr_imm + iconcat.

This was already done for [su]extend.i128, and is necessary for
codegen for 32-bit x86.

cranelift/filetests/filetests/isa/riscv/legalize-abi.clif

@@ -22,8 +22,8 @@ function %split_call_arg(i32) {
 block0(v0: i32):
     v1 = uextend.i64 v0
     call fn1(v1)
-    ; check: $(v1l=$V), $(v1h=$V) = isplit v1
-    ; check: call fn1($v1l, $v1h)
+    ; check: $(v1h=$V) = iconst.i32 0
+    ; check: call fn1(v0, $v1h)
     call fn2(v0, v1)
     ; check: call fn2(v0, $V, $V)
     return

cranelift/filetests/filetests/isa/x86/extend-i64-run.clif

@@ -0,0 +1,26 @@
+test run
+target i686
+
+function u0:0() -> b1 {
+block0:
+    v0 = iconst.i32 0xffff_ee00
+    v1 = uextend.i64 v0
+    v2, v3 = isplit v1
+    v4 = icmp_imm eq v2, 0xffff_ee00
+    v5 = icmp_imm eq v3, 0
+    v6 = band v4, v5
+    return v6
+}
+; run
+
+function u0:1() -> b1 {
+block0:
+    v0 = iconst.i32 0xffff_ee00
+    v1 = sextend.i64 v0
+    v2, v3 = isplit v1
+    v4 = icmp_imm eq v2, 0xffff_ee00
+    v5 = icmp_imm eq v3, 0xffff_ffff
+    v6 = band v4, v5
+    return v6
+}
+; run

cranelift/filetests/filetests/isa/x86/extend-i64.clif

@@ -0,0 +1,37 @@
+test compile
+target i686
+
+function u0:0() -> b1 {
+block0:
+    v0 = iconst.i32 0xffff_ee00
+    ; check: v0 = iconst.i32 0xffff_ee00
+    ; nextln: v2 -> v0
+    v1 = uextend.i64 v0
+    ; nextln: v7 = iconst.i32 0
+    ; nextln: v3 -> v7
+    ; nextln: v1 = iconcat v0, v7
+
+    v2, v3 = isplit v1
+    v4 = icmp_imm eq v2, 0xffff_ee00
+    v5 = icmp_imm eq v3, 0
+
+    v6 = band v4, v5
+    return v6
+}
+
+function u0:1() -> b1 {
+block0:
+    v0 = iconst.i32 0xffff_ee00
+    ; check: v0 = iconst.i32 0xffff_ee00
+    ; nextln: v2 -> v0
+    v1 = sextend.i64 v0
+    ; nextln: v10 = copy v0
+    ; nextln: v7 = sshr_imm v10, 31
+    ; nextln: v3 -> v7
+
+    v2, v3 = isplit v1
+    v4 = icmp_imm eq v2, 0xffff_ee00
+    v5 = icmp_imm eq v3, 0xffff_ffff
+    v6 = band v4, v5
+    return v6
+}