[llvm] [Xtensa] Implement branch analysis. (PR #110959)

[Andrei Safronov via llvm-commits]

================
@@ -185,3 +185,301 @@ void XtensaInstrInfo::loadImmediate(MachineBasicBlock &MBB,
     report_fatal_error("Unsupported load immediate value");
   }
 }
+
+bool XtensaInstrInfo::reverseBranchCondition(
+    SmallVectorImpl<MachineOperand> &Cond) const {
+  assert(Cond.size() <= 4 && "Invalid branch condition!");
+
+  switch (Cond[0].getImm()) {
+  case Xtensa::BEQ:
+    Cond[0].setImm(Xtensa::BNE);
+    return false;
+  case Xtensa::BNE:
+    Cond[0].setImm(Xtensa::BEQ);
+    return false;
+  case Xtensa::BLT:
+    Cond[0].setImm(Xtensa::BGE);
+    return false;
+  case Xtensa::BGE:
+    Cond[0].setImm(Xtensa::BLT);
+    return false;
+  case Xtensa::BLTU:
+    Cond[0].setImm(Xtensa::BGEU);
+    return false;
+  case Xtensa::BGEU:
+    Cond[0].setImm(Xtensa::BLTU);
+    return false;
+
+  case Xtensa::BEQI:
+    Cond[0].setImm(Xtensa::BNEI);
+    return false;
+  case Xtensa::BNEI:
+    Cond[0].setImm(Xtensa::BEQI);
+    return false;
+  case Xtensa::BGEI:
+    Cond[0].setImm(Xtensa::BLTI);
+    return false;
+  case Xtensa::BLTI:
+    Cond[0].setImm(Xtensa::BGEI);
+    return false;
+  case Xtensa::BGEUI:
+    Cond[0].setImm(Xtensa::BLTUI);
+    return false;
+  case Xtensa::BLTUI:
+    Cond[0].setImm(Xtensa::BGEUI);
+    return false;
+
+  case Xtensa::BEQZ:
+    Cond[0].setImm(Xtensa::BNEZ);
+    return false;
+  case Xtensa::BNEZ:
+    Cond[0].setImm(Xtensa::BEQZ);
+    return false;
+  case Xtensa::BLTZ:
+    Cond[0].setImm(Xtensa::BGEZ);
+    return false;
+  case Xtensa::BGEZ:
+    Cond[0].setImm(Xtensa::BLTZ);
+    return false;
+
+  default:
+    report_fatal_error("Invalid branch condition!");
+  }
+}
+
+bool XtensaInstrInfo::analyzeBranch(MachineBasicBlock &MBB,
+                                    MachineBasicBlock *&TBB,
+                                    MachineBasicBlock *&FBB,
+                                    SmallVectorImpl<MachineOperand> &Cond,
+                                    bool AllowModify = false) const {
+  // Most of the code and comments here are boilerplate.
+
+  // Start from the bottom of the block and work up, examining the
+  // terminator instructions.
+  MachineBasicBlock::iterator I = MBB.end();
+  while (I != MBB.begin()) {
+    --I;
+    if (I->isDebugValue())
+      continue;
----------------
andreisfr wrote:

I prepared new test which checks analyzeBranch and reverseBranchCondition functionality. I hope I understand your comment correctly.

https://github.com/llvm/llvm-project/pull/110959