Furture reduce the TP cost

Moved the *= operators as instance of `regMaskTP` so the `.low`
private field can directly be manipulated instead of converting
the `64-bit` value in `regMaskTP` before doing any operation.

Overall: 0.74%
MinOpts: 0.82%
FullOpts: 0.68%

Author: kunalspathak

src/coreclr/jit/compiler.hpp

@@ -1009,7 +1009,7 @@ inline regNumber genFirstRegNumFromMaskAndToggle(SingleTypeRegSet& mask)
 
     /* Convert the mask to a register number */
 
-    regNumber regNum = (regNumber)BitScanForward(mask);
+    regNumber regNum = (regNumber)BitOperations::BitScanForward(mask);
 
     mask ^= genRegMask(regNum);
 

src/coreclr/jit/target.h

@@ -249,8 +249,7 @@ struct regMaskTP
 public:
     regMaskTP(regMaskSmall regMask)
         : low(regMask)
-    {
-        
+    {   
     }
 
     regMaskTP()
@@ -323,6 +322,27 @@ struct regMaskTP
     void RemoveRegNumFromMask(regNumber reg);
 
     bool IsRegNumInMask(regNumber reg);
+
+    
+    void operator|=(const regMaskTP& second)
+    {
+        low |= second.getLow();
+    }
+
+    void operator^=(const regMaskTP& second)
+    {
+        low ^= second.getLow();
+    }
+
+    void operator^=(const regNumber reg)
+    {
+        low ^= genRegMask(reg);
+    }
+
+    void operator&=(const regMaskTP& second)
+    {
+        low &= second.getLow();
+    }
 };
 
 static regMaskTP operator^(const regMaskTP& first, const regMaskTP& second)
@@ -343,30 +363,6 @@ static regMaskTP operator|(const regMaskTP& first, const regMaskTP& second)
     return result;
 }
 
-static regMaskTP& operator|=(regMaskTP& first, const regMaskTP& second)
-{
-    first = first | second;
-    return first;
-}
-
-static regMaskTP& operator^=(regMaskTP& first, const regMaskTP& second)
-{
-    first = first ^ second;
-    return first;
-}
-
-static regMaskTP& operator^=(regMaskTP& first, const regNumber reg)
-{
-    first = first ^ genRegMask(reg);
-    return first;
-}
-
-static regMaskTP& operator&=(regMaskTP& first, const regMaskTP& second)
-{
-    first = first & second;
-    return first;
-}
-
 static bool operator==(const regMaskTP& first, const regMaskTP& second)
 {
     return (first.getLow() == second.getLow());