[llvm] [BOLT][AArch64] Support FEAT_CMPBR branch instructions. (PR #174972)

[Alexandros Lamprineas via llvm-commits]

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@@ -1844,8 +1844,21 @@ class AArch64MCPlusBuilder : public MCPlusBuilder {
     }
   }
 
+  bool isReversibleBranch(const MCInst &Inst) const override {
+    if (isCompAndBranch(Inst)) {
+      unsigned InvertedOpcode = getInvertedBranchOpcode(Inst.getOpcode());
+      if (needsImmDec(InvertedOpcode))
+        return Inst.getOperand(1).getImm() > 0;
+      if (needsImmInc(InvertedOpcode))
+        return Inst.getOperand(1).getImm() < 63;
+    }
+    return MCPlusBuilder::isReversibleBranch(Inst);
+  }
+
   void reverseBranchCondition(MCInst &Inst, const MCSymbol *TBB,
                               MCContext *Ctx) const override {
+    assert(isReversibleBranch(Inst) && "Cannot reverse branch");
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labrinea wrote:

I think it is too late to exit here. The caller of reverseBranchCondition relies on successful transformation therefore we must assert.

https://github.com/llvm/llvm-project/pull/174972