Cranelift: Implement iadd_cout on x64 for 32- and 64-bit integers (#5285)

* Split the `iadd_cout` runtests by type

* Implement `iadd_cout` for 32- and 64-bit values on x64

* Delete trailing whitespace in `riscv/lower.isle`

cranelift/codegen/src/isa/x64/inst.isle

@@ -2124,6 +2124,15 @@
          (MInst.Setcc cc dst)
          dst)))
 
+;; Helper for creating `MInst.Setcc` instructions, when the flags producer will
+;; also return a value.
+(decl x64_setcc_paired (CC) ConsumesFlags)
+(rule (x64_setcc_paired cc)
+      (let ((dst WritableGpr (temp_writable_gpr)))
+        (ConsumesFlags.ConsumesFlagsReturnsResultWithProducer
+         (MInst.Setcc cc dst)
+         dst)))
+
 ;; Helper for creating `MInst.XmmRmR` instructions.
 (decl xmm_rm_r (Type SseOpcode Xmm XmmMem) Xmm)
 (rule (xmm_rm_r ty op src1 src2)

cranelift/codegen/src/isa/x64/lower.isle

@@ -102,6 +102,19 @@
           (with_flags (x64_add_with_flags_paired $I64 x_lo y_lo)
                       (x64_adc_paired $I64 x_hi y_hi)))))
 
+;;;; Rules for `iadd_cout` ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+
+;; TODO: i8 and i16 support. Requires either learning how to encode ALU
+;; operations on values narrower than 32-bits (better code; big change) or doing
+;; the same extend-to-32-bits trick that aarch64 does (worse code; small
+;; change).
+
+(rule (lower (iadd_cout x y @ (value_type (ty_32_or_64 ty))))
+      (let ((results ValueRegs (with_flags (x64_add_with_flags_paired ty x y)
+                                           (x64_setcc_paired (CC.O)))))
+        (output_pair (value_regs_get results 0)
+                     (value_regs_get results 1))))
+
 ;;;; Rules for `sadd_sat` ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 
 (rule (lower (has_type (multi_lane 8 16)

cranelift/codegen/src/isa/x64/lower.rs

@@ -331,6 +331,7 @@ fn lower_insn_to_regs(
         | Opcode::F64const
         | Opcode::Null
         | Opcode::Iadd
+        | Opcode::IaddCout
         | Opcode::IaddIfcout
         | Opcode::SaddSat
         | Opcode::UaddSat
@@ -515,7 +516,6 @@ fn lower_insn_to_regs(
         | Opcode::IrsubImm
         | Opcode::IaddCin
         | Opcode::IaddIfcin
-        | Opcode::IaddCout
         | Opcode::IaddCarry
         | Opcode::IaddIfcarry
         | Opcode::IsubBin