[X86][ARM] Invert the low bit to get the inverse predicate (NFC)

Both ARM and x86 defined their predicate in such a way to allow bit twiddling to get inverse predicates

Author: AZero13

llvm/lib/Target/ARM/Utils/ARMBaseInfo.h

@@ -46,23 +46,9 @@ enum CondCodes { // Meaning (integer)          Meaning (floating-point)
 };
 
 inline static CondCodes getOppositeCondition(CondCodes CC) {
-  switch (CC) {
-  default: llvm_unreachable("Unknown condition code");
-  case EQ: return NE;
-  case NE: return EQ;
-  case HS: return LO;
-  case LO: return HS;
-  case MI: return PL;
-  case PL: return MI;
-  case VS: return VC;
-  case VC: return VS;
-  case HI: return LS;
-  case LS: return HI;
-  case GE: return LT;
-  case LT: return GE;
-  case GT: return LE;
-  case LE: return GT;
-  }
+  // To reverse a condition it's necessary to only invert the low bit:
+
+  return static_cast<CondCodes>(static_cast<unsigned>(CC) ^ 0x1);
 }
 
 /// getSwappedCondition - assume the flags are set by MI(a,b), return

llvm/lib/Target/X86/X86InstrInfo.cpp

@@ -3297,51 +3297,6 @@ unsigned X86::getNonNDVariant(unsigned Opc) {
   return getNewOpcFromTable(X86ND2NonNDTable, Opc);
 }
 
-/// Return the inverse of the specified condition,
-/// e.g. turning COND_E to COND_NE.
-X86::CondCode X86::GetOppositeBranchCondition(X86::CondCode CC) {
-  switch (CC) {
-  default:
-    llvm_unreachable("Illegal condition code!");
-  case X86::COND_E:
-    return X86::COND_NE;
-  case X86::COND_NE:
-    return X86::COND_E;
-  case X86::COND_L:
-    return X86::COND_GE;
-  case X86::COND_LE:
-    return X86::COND_G;
-  case X86::COND_G:
-    return X86::COND_LE;
-  case X86::COND_GE:
-    return X86::COND_L;
-  case X86::COND_B:
-    return X86::COND_AE;
-  case X86::COND_BE:
-    return X86::COND_A;
-  case X86::COND_A:
-    return X86::COND_BE;
-  case X86::COND_AE:
-    return X86::COND_B;
-  case X86::COND_S:
-    return X86::COND_NS;
-  case X86::COND_NS:
-    return X86::COND_S;
-  case X86::COND_P:
-    return X86::COND_NP;
-  case X86::COND_NP:
-    return X86::COND_P;
-  case X86::COND_O:
-    return X86::COND_NO;
-  case X86::COND_NO:
-    return X86::COND_O;
-  case X86::COND_NE_OR_P:
-    return X86::COND_E_AND_NP;
-  case X86::COND_E_AND_NP:
-    return X86::COND_NE_OR_P;
-  }
-}
-
 /// Assuming the flags are set by MI(a,b), return the condition code if we
 /// modify the instructions such that flags are set by MI(b,a).
 static X86::CondCode getSwappedCondition(X86::CondCode CC) {

llvm/lib/Target/X86/X86InstrInfo.h

@@ -85,7 +85,11 @@ unsigned getNonNDVariant(unsigned Opc);
 
 /// GetOppositeBranchCondition - Return the inverse of the specified cond,
 /// e.g. turning COND_E to COND_NE.
-CondCode GetOppositeBranchCondition(CondCode CC);
+CondCode GetOppositeBranchCondition(CondCode CC) {
+  // To reverse a condition it's necessary to only invert the low bit:
+
+  return static_cast<CondCode>(static_cast<unsigned>(CC) ^ 0x1);
+}
 
 /// Get the VPCMP immediate for the given condition.
 unsigned getVPCMPImmForCond(ISD::CondCode CC);