[LV] Update CFG before adding runtime checks.

addRuntimeChecks uses SCEVExpander, which relies on the DT/LoopInfo to
be up-to-date. Changing the CFG afterwards may invalidate some inserted
instructions, especially LCSSA phis.

Reorder the code to first update the CFG and then create the runtime
checks. This should not have any impact on the generated code, as we
adjust the CFG and generate runtime checks together.

Fixes PR47343.

Author: fhahn

llvm/lib/Transforms/Vectorize/LoopVectorize.cpp

@@ -2950,31 +2950,32 @@ void InnerLoopVectorizer::emitMemRuntimeChecks(Loop *L, BasicBlock *Bypass) {
     });
   }
 
-  Instruction *FirstCheckInst;
-  Instruction *MemRuntimeCheck;
-  std::tie(FirstCheckInst, MemRuntimeCheck) =
-      addRuntimeChecks(MemCheckBlock->getTerminator(), OrigLoop,
-                       RtPtrChecking.getChecks(), RtPtrChecking.getSE());
-  assert(MemRuntimeCheck && "no RT checks generated although RtPtrChecking "
-                            "claimed checks are required");
-
   MemCheckBlock->setName("vector.memcheck");
   // Create new preheader for vector loop.
   LoopVectorPreHeader =
       SplitBlock(MemCheckBlock, MemCheckBlock->getTerminator(), DT, LI, nullptr,
                  "vector.ph");
 
+  auto *CondBranch = cast<BranchInst>(
+      Builder.CreateCondBr(Builder.getTrue(), Bypass, LoopVectorPreHeader));
+  ReplaceInstWithInst(MemCheckBlock->getTerminator(), CondBranch);
+  LoopBypassBlocks.push_back(MemCheckBlock);
+  AddedSafetyChecks = true;
+
   // Update dominator only if this is first RT check.
   if (LoopBypassBlocks.empty()) {
     DT->changeImmediateDominator(Bypass, MemCheckBlock);
     DT->changeImmediateDominator(LoopExitBlock, MemCheckBlock);
   }
 
-  ReplaceInstWithInst(
-      MemCheckBlock->getTerminator(),
-      BranchInst::Create(Bypass, LoopVectorPreHeader, MemRuntimeCheck));
-  LoopBypassBlocks.push_back(MemCheckBlock);
-  AddedSafetyChecks = true;
+  Instruction *FirstCheckInst;
+  Instruction *MemRuntimeCheck;
+  std::tie(FirstCheckInst, MemRuntimeCheck) =
+      addRuntimeChecks(MemCheckBlock->getTerminator(), OrigLoop,
+                       RtPtrChecking.getChecks(), RtPtrChecking.getSE());
+  assert(MemRuntimeCheck && "no RT checks generated although RtPtrChecking "
+                            "claimed checks are required");
+  CondBranch->setCondition(MemRuntimeCheck);
 
   // We currently don't use LoopVersioning for the actual loop cloning but we
   // still use it to add the noalias metadata.

llvm/test/Transforms/LoopVectorize/pr47343-expander-lcssa-after-cfg-update.ll

@@ -0,0 +1,100 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt -loop-vectorize -force-vector-width=2 %s -S | FileCheck %s
+
+; Test case for PR47343. Make sure LCSSA phis are create correctly when
+; expanding the memory runtime checks.
+
+@f.e = external global i32, align 1
+@d = external global i8*, align 1
+
+declare i1 @cond()
+
+define void @f() {
+; CHECK-LABEL: @f(
+
+; CHECK:       outer.header:
+; CHECK-NEXT:    [[TMP0:%.*]] = load i8*, i8** @d, align 1
+; CHECK-NEXT:    [[C_0:%.*]] = call i1 @cond()
+; CHECK-NEXT:    br i1 [[C_0]], label %outer.exit.0, label %inner.1.header.preheader
+
+; CHECK:       outer.exit.0:
+; CHECK-NEXT:    [[DOTLCSSA:%.*]] = phi i8* [ [[TMP0]], %outer.header ]
+; CHECK-NEXT:    br label %loop.preheader
+
+; CHECK:       outer.exit.1:
+; CHECK-NEXT:    [[DOTLCSSA1:%.*]] = phi i8* [ [[TMP0]], %inner.1.latch ]
+; CHECK-NEXT:    br label %loop.preheader
+
+; CHECK:       loop.preheader:
+; CHECK-NEXT:    [[TMP1:%.*]] = phi i8* [ [[DOTLCSSA]], %outer.exit.0 ], [ [[DOTLCSSA1]], %outer.exit.1 ]
+; CHECK-NEXT:    br i1 false, label [[SCALAR_PH:%.*]], label [[VECTOR_MEMCHECK:%.*]]
+
+; CHECK:       vector.memcheck:
+; CHECK-NEXT:    [[SCEVGEP:%.*]] = getelementptr i8, i8* [[TMP1]], i64 1
+; CHECK-NEXT:    [[BOUND0:%.*]] = icmp ult i8* bitcast (i32* @f.e to i8*), [[SCEVGEP]]
+; CHECK-NEXT:    [[BOUND1:%.*]] = icmp ult i8* [[TMP0]], getelementptr (i8, i8* bitcast (i32* @f.e to i8*), i64 1)
+; CHECK-NEXT:    [[FOUND_CONFLICT:%.*]] = and i1 [[BOUND0]], [[BOUND1]]
+; CHECK-NEXT:    [[MEMCHECK_CONFLICT:%.*]] = and i1 [[FOUND_CONFLICT]], true
+; CHECK-NEXT:    br i1 [[MEMCHECK_CONFLICT]], label [[SCALAR_PH]], label [[VECTOR_PH:%.*]]
+
+; CHECK:       vector.ph:
+; CHECK-NEXT:    br label [[VECTOR_BODY:%.*]]
+
+; CHECK:       vector.body:
+; CHECK-NEXT:    [[INDEX:%.*]] = phi i32 [ 0, [[VECTOR_PH]] ], [ [[INDEX_NEXT:%.*]], [[VECTOR_BODY]] ]
+; CHECK-NEXT:    [[TMP2:%.*]] = add i32 [[INDEX]], 0
+; CHECK-NEXT:    store i32 0, i32* @f.e, align 1, !alias.scope !0, !noalias !3
+; CHECK-NEXT:    store i32 0, i32* @f.e, align 1, !alias.scope !0, !noalias !3
+; CHECK-NEXT:    store i8 10, i8* [[TMP0]], align 1
+; CHECK-NEXT:    store i8 10, i8* [[TMP0]], align 1
+; CHECK-NEXT:    [[INDEX_NEXT]] = add i32 [[INDEX]], 2
+; CHECK-NEXT:    [[TMP3:%.*]] = icmp eq i32 [[INDEX_NEXT]], 500
+; CHECK-NEXT:    br i1 [[TMP3]], label [[MIDDLE_BLOCK:%.*]], label [[VECTOR_BODY]], [[LOOP5:!llvm.loop !.*]]
+
+; CHECK:       middle.block:
+; CHECK-NEXT:    [[CMP_N:%.*]] = icmp eq i32 500, 500
+; CHECK-NEXT:    br i1 [[CMP_N]], label [[EXIT:%.*]], label [[SCALAR_PH]]
+
+; CHECK:       scalar.ph:
+; CHECK-NEXT:    [[TMP4:%.*]] = phi i8* [ [[TMP1]], %vector.memcheck ], [ [[TMP1]], %loop.preheader ], [ [[TMP1]], %middle.block ]
+; CHECK-NEXT:    [[BC_RESUME_VAL:%.*]] = phi i32 [ 500, %middle.block ], [ 0, %loop.preheader ], [ 0, %vector.memcheck ]
+; CHECK-NEXT:    br label [[LOOP:%.*]]
+;
+entry:
+  br label %outer.header
+
+outer.header:                            ; preds = %cleanup, %entry
+  %0 = load i8*, i8** @d, align 1
+  %c.0 = call i1 @cond()
+  br i1 %c.0, label %outer.exit.0, label %inner.1.header
+
+inner.1.header:                                         ; preds = %if.end, %for.body3.lr.ph.outer
+  %c.1 = call i1 @cond()
+  br i1 %c.1, label %inner.1.latch, label %outer.latch
+
+inner.1.latch:                                           ; preds = %land.end
+  %c.2 = call i1 @cond()
+  br i1 %c.2, label %outer.exit.1, label %inner.1.header
+
+outer.latch:                                          ; preds = %land.end
+  br label %outer.header
+
+
+outer.exit.0:                                         ; preds = %if.end, %if.end.us.us.us
+  br label %loop
+
+outer.exit.1:                                         ; preds = %if.end, %if.end.us.us.us
+  br label %loop
+
+loop:                                  ; preds = %if.end.us.us.us, %for.body3.lr.ph.outer
+  %iv = phi i32 [ %iv.next, %loop ], [ 0, %outer.exit.0 ], [ 0, %outer.exit.1 ]
+  %conv6.us.us.us = zext i1 false to i32
+  store i32 %conv6.us.us.us, i32* @f.e, align 1
+  store i8 10, i8* %0, align 1
+  %iv.next = add nsw i32 %iv, 1
+  %ec = icmp eq i32 %iv.next, 500
+  br i1 %ec, label %exit, label %loop
+
+exit:
+  ret void
+}