[codegen] legalize imul for 64-bit and 128-bit operands

Add a legalization that legalizes imul.I64 for 32-bit ISAs and imul.I128
for 64-bit (and subsequently 32-bit) ISAs.

Refs: https://github.com/bnjbvr/cranelift-x86/issues/4

cranelift/codegen/meta/src/shared/legalize.rs

@@ -115,6 +115,7 @@ pub(crate) fn define(insts: &InstructionGroup, imm: &Immediates) -> TransformGro
     let uextend = insts.by_name("uextend");
     let uload8 = insts.by_name("uload8");
     let uload16 = insts.by_name("uload16");
+    let umulhi = insts.by_name("umulhi");
     let ushr = insts.by_name("ushr");
     let ushr_imm = insts.by_name("ushr_imm");
     let urem = insts.by_name("urem");
@@ -336,6 +337,25 @@ pub(crate) fn define(insts: &InstructionGroup, imm: &Immediates) -> TransformGro
         }
     }
 
+    // TODO(ryzokuken): explore the perf diff w/ x86_umulx and consider have a
+    // separate legalization for x86.
+    for &ty in &[I64, I128] {
+        narrow.legalize(
+            def!(a = imul.ty(x, y)),
+            vec![
+                def!((xl, xh) = isplit(x)),
+                def!((yl, yh) = isplit(y)),
+                def!(a1 = imul(xh, yl)),
+                def!(a2 = imul(xl, yh)),
+                def!(a3 = iadd(a1, a2)),
+                def!(a4 = umulhi(xl, yl)),
+                def!(ah = iadd(a3, a4)),
+                def!(al = imul(xl, yl)),
+                def!(a = iconcat(al, ah)),
+            ],
+        );
+    }
+
     // Widen instructions with one input operand.
     for &op in &[bnot, popcnt] {
         for &int_ty in &[I8, I16] {

cranelift/filetests/filetests/isa/x86/imul-i128.clif

@@ -0,0 +1,20 @@
+test run
+target x86_64 haswell
+
+function %test_imul_i128() -> b1 {
+ebb0:
+    v11 = iconst.i64 0xf2347ac4503f1e24
+    v12 = iconst.i64 0x0098fe985354ab06
+    v1 = iconcat v11, v12
+    v21 = iconst.i64 0xf606ba453589ef89
+    v22 = iconst.i64 0x042e1f3054ca7432
+    v2 = iconcat v21, v22
+    v31 = iconst.i64 0xbe2044b2742ebd44
+    v32 = iconst.i64 0xa363ce3b6849f307
+    v3 = iconcat v31, v32
+    v4 = imul v1, v2
+    v5 = icmp eq v3, v4
+    return v5
+}
+
+; run

cranelift/filetests/filetests/isa/x86/legalize-i128.clif

@@ -0,0 +1,20 @@
+; Test the legalization of i128 instructions on x86_64.
+test legalizer
+target x86_64 haswell
+
+; regex: V=v\d+
+
+function %imul(i128, i128) -> i128 {
+ebb0(v1: i128, v2: i128):
+    v10 = imul v1, v2
+    ; check: v1 = iconcat $(v1_lsb=$V), $(v1_msb=$V)
+    ; nextln: v2 = iconcat $(v2_lsb=$V), $(v2_msb=$V)
+    ; nextln: $(v11=$V) = imul $v1_msb, $v2_lsb
+    ; nextln: $(v12=$V) = imul $v1_lsb, $v2_msb
+    ; nextln: $(v13=$V) = iadd $v11, $v12
+    ; nextln: $(v99=$V), $(v14=$V) = x86_umulx $v1_lsb, $v2_lsb
+    ; nextln: $(v10_msb=$V) = iadd $v13, $v14
+    ; nextln: $(v10_lsb=$V) = imul $v1_lsb, $v2_lsb
+    ; nextln: v10 = iconcat $v10_lsb, $v10_msb
+    return v10
+}

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

@@ -26,6 +26,21 @@ ebb0(v1: i64, v2: i64):
     return v10
 }
 
+function %imul(i64, i64) -> i64 {
+ebb0(v1: i64, v2: i64):
+    v10 = imul v1, v2
+    ; check: v1 = iconcat $(v1_lsb=$V), $(v1_msb=$V)
+    ; nextln: v2 = iconcat $(v2_lsb=$V), $(v2_msb=$V)
+    ; nextln: $(v11=$V) = imul $v1_msb, $v2_lsb
+    ; nextln: $(v12=$V) = imul $v1_lsb, $v2_msb
+    ; nextln: $(v13=$V) = iadd $v11, $v12
+    ; nextln: $(v99=$V), $(v14=$V) = x86_umulx $v1_lsb, $v2_lsb
+    ; nextln: $(v10_msb=$V) = iadd $v13, $v14
+    ; nextln: $(v10_lsb=$V) = imul $v1_lsb, $v2_lsb
+    ; nextln: v10 = iconcat $v10_lsb, $v10_msb
+    return v10
+}
+
 function %icmp_eq(i64, i64) -> b1 {
 ebb0(v1: i64, v2: i64):
     v10 = icmp eq v1, v2