[llvm] [X86][ARM] Invert the low bit to get the inverse predicate (NFC) (PR #151748)

[Craig Topper via llvm-commits]

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@@ -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:
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topperc wrote:

Add an assert for COND_INVALID

https://github.com/llvm/llvm-project/pull/151748