[PATCH] D107303: [RISCV] Indicate that RISCVMergeBaseOffsetOpt preserves the CFG.

[Craig Topper via Phabricator via llvm-commits]

craig.topper created this revision.
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Return false from runOnFunction if nothing changed. Curiously
we already returned a bool from detectAndFoldOffset, but didn't
use it.

Fix a couple breaks after returns that I saw while auditing
detectAndFoldOffset.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D107303

Files:
  llvm/lib/Target/RISCV/RISCVMergeBaseOffset.cpp


Index: llvm/lib/Target/RISCV/RISCVMergeBaseOffset.cpp
===================================================================
--- llvm/lib/Target/RISCV/RISCVMergeBaseOffset.cpp
+++ llvm/lib/Target/RISCV/RISCVMergeBaseOffset.cpp
@@ -53,6 +53,11 @@
         MachineFunctionProperties::Property::IsSSA);
   }
 
+  void getAnalysisUsage(AnalysisUsage &AU) const override {
+    AU.setPreservesCFG();
+    MachineFunctionPass::getAnalysisUsage(AU);
+  }
+
   StringRef getPassName() const override {
     return RISCV_MERGE_BASE_OFFSET_NAME;
   }
@@ -193,7 +198,7 @@
     LLVM_DEBUG(dbgs() << "  Offset Instr: " << Tail);
     foldOffset(HiLUI, LoADDI, Tail, Offset);
     return true;
-  } break;
+  }
   case RISCV::ADD: {
     // The offset is too large to fit in the immediate field of ADDI.
     // This can be in two forms:
@@ -208,7 +213,7 @@
       return false;
     foldOffset(HiLUI, LoADDI, Tail, Offset);
     return true;
-  } break;
+  }
   case RISCV::LB:
   case RISCV::LH:
   case RISCV::LW:
@@ -252,7 +257,7 @@
     Tail.getOperand(1).setReg(HiLUI.getOperand(0).getReg());
     DeadInstrs.insert(&LoADDI);
     return true;
-  } break;
+  }
   }
   return false;
 }
@@ -261,6 +266,7 @@
   if (skipFunction(Fn.getFunction()))
     return false;
 
+  bool MadeChange = false;
   DeadInstrs.clear();
   MRI = &Fn.getRegInfo();
   for (MachineBasicBlock &MBB : Fn) {
@@ -272,13 +278,13 @@
       LLVM_DEBUG(dbgs() << "  Found lowered global address with one use: "
                         << *LoADDI->getOperand(2).getGlobal() << "\n");
       // If the use count is only one, merge the offset
-      detectAndFoldOffset(HiLUI, *LoADDI);
+      MadeChange |= detectAndFoldOffset(HiLUI, *LoADDI);
     }
   }
   // Delete dead instructions.
   for (auto *MI : DeadInstrs)
     MI->eraseFromParent();
-  return true;
+  return MadeChange;
 }
 
 /// Returns an instance of the Merge Base Offset Optimization pass.


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