x64: Remove unnecessary register use when comparing against constants (#4645)

https://github.com/bytecodealliance/wasmtime/pull/4645

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

@@ -1080,6 +1080,9 @@
 (decl cc_invert (CC) CC)
 (extern constructor cc_invert cc_invert)
 
+(decl intcc_reverse (IntCC) IntCC)
+(extern constructor intcc_reverse intcc_reverse)
+
 (decl floatcc_inverse (FloatCC) FloatCC)
 (extern constructor floatcc_inverse floatcc_inverse)
 
@@ -3178,6 +3181,13 @@
       (let ((size OperandSize (raw_operand_size_of_type ty)))
         (icmp_cond_result (x64_cmp size b a) cc)))
 
+;; As a special case, reverse the arguments to the comparison when the LHS is a
+;; constant. This ensures that we avoid moving the constant into a register when
+;; performing the comparison.
+(rule (emit_cmp cc (and (simm32_from_value a) (value_type ty)) b)
+      (let ((size OperandSize (raw_operand_size_of_type ty)))
+        (icmp_cond_result (x64_cmp size a b) (intcc_reverse cc))))
+
 ;; For I128 values (held in two GPRs), the instruction sequences depend on what
 ;; kind of condition is tested.
 (rule (emit_cmp (IntCC.Equal) a @ (value_type $I128) b)

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

@@ -610,6 +610,11 @@ where
         }
     }
 
+    #[inline]
+    fn intcc_reverse(&mut self, cc: &IntCC) -> IntCC {
+        cc.reverse()
+    }
+
     #[inline]
     fn floatcc_inverse(&mut self, cc: &FloatCC) -> FloatCC {
         cc.inverse()