Fix PR45442: Bail out when MemorySSA information is not available

[hiraditya]

Self approving as it is a trivial change and fixes PR45442

[fhahn]

llvm/lib/Transforms/Scalar/GVNHoist.cpp

525

IMO I think it would preferable to check at the call site where we get the MemoryUseOrDef and not call safeToHoistLdSt without MemoryUseOrDef.

llvm/test/Transforms/GVNHoist/pr45442.ll

21

nit: branch on undef is UB, so it is probably best to avoid it and use a i1 parameter or something instead

[hiraditya]

llvm/lib/Transforms/Scalar/GVNHoist.cpp

525

Sure, i'll do that.

llvm/test/Transforms/GVNHoist/pr45442.ll

21

Makes sense, i'll amend the testcase. The test case was reported in the PR so i added as is. Thanks for pointing out.

[fhahn]

llvm/test/Transforms/GVNHoist/pr45442.ll

21

No worries! Also might be good to replace the unreachable with ret void, if it still reproduces the crash.

[hiraditya]

Updated test cases.

[fhahn]

Thanks, LGTM although the test appease to still use branch on undef. Would be good to adjust before committing.

llvm/lib/Transforms/Scalar/GVNHoist.cpp

608–611

nit: auto * T?

[hiraditya]

Fixed the bug in: https://bugs.llvm.org/show_bug.cgi?id=45442

llvm/lib/Transforms/Scalar/GVNHoist.cpp

private:
   // Return true when it is safe to hoist a memory load or store U from OldPt
   // to NewPt.
   bool safeToHoistLdSt(const Instruction *NewPt, const Instruction *OldPt,
                        MemoryUseOrDef *U, InsKind K, int &NBBsOnAllPaths) {
     // In place hoisting is safe.
     if (NewPt == OldPt)
       return true;
 
-    // MemoryUseDef information is not available, bail out.
-    if (!U)
-      return false;
-
     const BasicBlock *NewBB = NewPt->getParent();
     const BasicBlock *OldBB = OldPt->getParent();
     const BasicBlock *UBB = U->getBlock();
 
     // Check for dependences on the Memory SSA.
     MemoryAccess *D = U->getDefiningAccess();
     BasicBlock *DBB = D->getBlock();
     if (DT->properlyDominates(NewBB, DBB))
       // Cannot move the load or store to NewBB above its definition in DBB.
       return false;
void checkSafety(CHIArgs C, BasicBlock *BB, InsKind K,
     for (auto CHI : C) {
       Instruction *Insn = CHI.I;
       if (!Insn) // No instruction was inserted in this CHI.
         continue;
       if (K == InsKind::Scalar) {
         if (safeToHoistScalar(BB, Insn->getParent(), NumBBsOnAllPaths))
           Safe.push_back(CHI);
       } else {
-        MemoryUseOrDef *UD = MSSA->getMemoryAccess(Insn);
-        if (safeToHoistLdSt(BB->getTerminator(), Insn, UD, K, NumBBsOnAllPaths))
+        auto *T = BB->getTerminator();
+        if (MemoryUseOrDef *UD = MSSA->getMemoryAccess(Insn))
+          if (safeToHoistLdSt(T, Insn, UD, K, NumBBsOnAllPaths))
             Safe.push_back(CHI);
       }
     }
   }
 
   using RenameStackType = DenseMap<VNType, SmallVector<Instruction *, 2>>;
 
   // Push all the VNs corresponding to BB into RenameStack.
   void fillRenameStack(BasicBlock *BB, InValuesType &ValueBBs,

llvm/test/Transforms/GVNHoist/pr45442.ll

 ; RUN: opt < %s -gvn-hoist -S | FileCheck %s
 
 ; gvn-hoist shouldn't crash in this case.
-; CHECK-LABEL: @func()
+; CHECK-LABEL: @func(i1 %b)
 ; CHECK:       entry:
 ; CHECK-NEXT:  br i1
 ; CHECK:  bb1:
-; CHECK-NEXT:  unreachable
+; CHECK-NEXT:  ret void
 ; CHECK:  bb2:
 ; CHECK-NEXT:  call
 ; CHECK-NEXT:  call
-; CHECK-NEXT:  unreachable
+; CHECK-NEXT:  ret void
 
 define void @v_1_0() #0 {
 entry:
   ret void
 }
 
-define void @func()  {
+define void @func(i1 %b) {
 entry:
-  br i1 undef, label %bb1, label %bb2
+  br i1 %b, label %bb1, label %bb2
 
 bb1:
-  unreachable
+  ret void
 
 bb2:
   call void @v_1_0()
   call void @v_1_0()
-  unreachable
+  ret void
 }
 
 attributes #0 = { nounwind readonly }