Optimize flips between 1 and 0 (#100491)

We can solve this with a bit flip rather than + 1 mod 2.

Author: AZero13

src/coreclr/jit/compiler.cpp

@@ -2193,7 +2193,7 @@ const char* Compiler::compRegVarName(regNumber reg, bool displayVar, bool isFloa
                                                                 // consecutive calls before printing
             static int index = 0;                               // for circular index into the name array
 
-            index = (index + 1) % 2; // circular reuse of index
+            index ^= 1; // circular reuse of index
             sprintf_s(nameVarReg[index], NAME_VAR_REG_BUFFER_LEN, "%s'%s'", getRegName(reg), VarNameToStr(varName));
 
             return nameVarReg[index];

src/coreclr/jit/emitxarch.cpp

@@ -10102,7 +10102,7 @@ const char* emitter::emitRegName(regNumber reg, emitAttr attr, bool varName) con
                 suffix = 'd';
                 goto APPEND_SUFFIX;
             }
-            rbc        = (rbc + 1) % 2;
+            rbc ^= 1;
             rb[rbc][0] = 'e';
             rb[rbc][1] = rn[1];
             rb[rbc][2] = rn[2];
@@ -10133,7 +10133,7 @@ const char* emitter::emitRegName(regNumber reg, emitAttr attr, bool varName) con
             {
                 suffix = 'b';
             APPEND_SUFFIX:
-                rbc        = (rbc + 1) % 2;
+                rbc ^= 1;
                 rb[rbc][0] = rn[0];
                 rb[rbc][1] = rn[1];
                 if (rn[2])
@@ -10151,7 +10151,7 @@ const char* emitter::emitRegName(regNumber reg, emitAttr attr, bool varName) con
             }
             else
             {
-                rbc        = (rbc + 1) % 2;
+                rbc ^= 1;
                 rb[rbc][0] = rn[1];
                 if (reg < 4)
                 {
@@ -10168,7 +10168,7 @@ const char* emitter::emitRegName(regNumber reg, emitAttr attr, bool varName) con
 #endif // TARGET_AMD64
 
 #if defined(TARGET_X86)
-            rbc        = (rbc + 1) % 2;
+            rbc ^= 1;
             rb[rbc][0] = rn[1];
             rb[rbc][1] = 'l';
             strcpy_s(&rb[rbc][2], sizeof(rb[0]) - 2, rn + 3);

src/coreclr/vm/gc_unwind_x86.inl

@@ -1670,10 +1670,7 @@ unsigned scanArgRegTableI(PTR_CBYTE    table,
                 {
                     thisPtrReg = REGI_NA;
                 }
-                if  (iptrRegs & regMask)
-                {
-                    iptrRegs &= ~regMask;
-                }
+                iptrRegs &= ~regMask;
             }
             iptr = isThis = false;
             continue;