[Xtensa] Fixup hwloop pass

Create block and insert it before loop end address as target for jump/branch instruction to avoid premature exit from loop.
espressif · Mar 29, 2023 · f389074 · f389074
1 parent a07cafd
commit f389074
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Showing 2 changed files with 40 additions and 6 deletions.
diff --git a/llvm/lib/Target/Xtensa/XtensaFixupHWLoops.cpp b/llvm/lib/Target/Xtensa/XtensaFixupHWLoops.cpp
@@ -290,7 +290,6 @@ bool XtensaFixupHwLoops::fixupLoopInstrs(MachineLoop *L) {
               Changed = true;
               break;
             }
-
             if (PII != PIB) {
               LoopEnd = MF->CreateMachineBasicBlock();
               MF->insert(++(PMBB->getIterator()), LoopEnd);
@@ -302,10 +301,45 @@ bool XtensaFixupHwLoops::fixupLoopInstrs(MachineLoop *L) {
                   .addMBB(LoopEnd);
               LoopEnd->addSuccessor(LoopEnd);
             } else {
-              BuildMI(*PMBB, PII, DL, TII->get(Xtensa::LOOPEND)).addMBB(PMBB);
-              PMBB->addSuccessor(PMBB);
-              BuildMI(*PMBB, PII, DL, TII->get(Xtensa::NOP));
-              LoopEnd = PMBB;
+              bool NeedBlockForJump = false;
+              // Check for branches to the loop end basic block from
+              // predecessors
+              for (auto I = PMBB->pred_begin(), E = PMBB->pred_end(); I != E;
+                   ++I) {
+                MachineBasicBlock *PLEMBB = *I;
+                MachineBasicBlock *TBB = nullptr, *FBB = nullptr;
+                SmallVector<MachineOperand, 4> Cond;
+                if (!TII->analyzeBranch(*PLEMBB, TBB, FBB, Cond)) {
+                  if (TBB == PMBB) {
+                    NeedBlockForJump = true;
+                    break;
+                  }
+                } else {
+                  NeedBlockForJump = true;
+                  break;
+                }
+              }
+              // Create block and insert it before loop end address as
+              // target for jump/branch instruction to avoid premature exit from
+              // loop
+              if (NeedBlockForJump) {
+                LoopEnd = MF->CreateMachineBasicBlock();
+                MF->insert(++(PMBB->getIterator()), LoopEnd);
+                LoopEnd->transferSuccessors(PMBB);
+                LoopEnd->splice(LoopEnd->end(), PMBB, PII, PMBB->end());
+                PMBB->addSuccessor(LoopEnd);
+                BuildMI(*PMBB, PMBB->end(), DL, TII->get(Xtensa::NOP));
+
+                BuildMI(*LoopEnd, LoopEnd->begin(), DL,
+                        TII->get(Xtensa::LOOPEND))
+                    .addMBB(LoopEnd);
+                LoopEnd->addSuccessor(LoopEnd);
+              } else {
+                BuildMI(*PMBB, PII, DL, TII->get(Xtensa::LOOPEND)).addMBB(PMBB);
+                PMBB->addSuccessor(PMBB);
+                BuildMI(*PMBB, PII, DL, TII->get(Xtensa::NOP));
+                LoopEnd = PMBB;
+              }
             }
 
             Changed = true;

diff --git a/llvm/lib/Target/Xtensa/XtensaHardwareLoops.cpp b/llvm/lib/Target/Xtensa/XtensaHardwareLoops.cpp
@@ -360,7 +360,7 @@ bool XtensaHardwareLoops::processLoop(MachineLoop *L) {
 }
 
 bool XtensaHardwareLoops::checkLoopSize(MachineLoop *L) {
-  uint64_t LoopSize = 0;
+  uint64_t LoopSize = 3; //Reserve space for possible NOP
 
   for (auto *MBB : L->getBlocks()) {
     uint64_t BlockSize = 0;