[IndVars] Check if WideInc available before trying to use it

WideInc/WideIncExpr can be null. Previously this worked out
because the comparison with WideIncExpr would fail. Now we have
accesses to WideInc prior to that. Avoid the issue with an
explicit check.

Fixes https://github.com/llvm/llvm-project/issues/106239.

1 files changed, 17 insertions, 11 deletions

diff --git a/llvm/lib/Transforms/Utils/SimplifyIndVar.cpp b/llvm/lib/Transforms/Utils/SimplifyIndVar.cpp
index 8e3a14b..a950a4f 100644
--- a/llvm/lib/Transforms/Utils/SimplifyIndVar.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyIndVar.cpp
@@ -1928,18 +1928,24 @@ Instruction *WidenIV::widenIVUse(WidenIV::NarrowIVDefUse DU,
     if (!WideAddRec.first)
       return nullptr;
 
-    // Reuse the IV increment that SCEVExpander created. Recompute flags, unless
-    // the flags for both increments agree and it is safe to use the ones from
-    // the original inc. In that case, the new use of the wide increment won't
-    // be more poisonous.
-    bool NeedToRecomputeFlags =
-        !SCEVExpander::canReuseFlagsFromOriginalIVInc(OrigPhi, WidePhi,
-                                                      DU.NarrowUse, WideInc) ||
-        DU.NarrowUse->hasNoUnsignedWrap() != WideInc->hasNoUnsignedWrap() ||
-        DU.NarrowUse->hasNoSignedWrap() != WideInc->hasNoSignedWrap();
+    auto CanUseWideInc = [&]() {
+      if (!WideInc)
+        return false;
+      // Reuse the IV increment that SCEVExpander created. Recompute flags,
+      // unless the flags for both increments agree and it is safe to use the
+      // ones from the original inc. In that case, the new use of the wide
+      // increment won't be more poisonous.
+      bool NeedToRecomputeFlags =
+          !SCEVExpander::canReuseFlagsFromOriginalIVInc(
+              OrigPhi, WidePhi, DU.NarrowUse, WideInc) ||
+          DU.NarrowUse->hasNoUnsignedWrap() != WideInc->hasNoUnsignedWrap() ||
+          DU.NarrowUse->hasNoSignedWrap() != WideInc->hasNoSignedWrap();
+      return WideAddRec.first == WideIncExpr &&
+             Rewriter.hoistIVInc(WideInc, DU.NarrowUse, NeedToRecomputeFlags);
+    };
+
     Instruction *WideUse = nullptr;
-    if (WideAddRec.first == WideIncExpr &&
-        Rewriter.hoistIVInc(WideInc, DU.NarrowUse, NeedToRecomputeFlags))
+    if (CanUseWideInc())
       WideUse = WideInc;
     else {
       WideUse = cloneIVUser(DU, WideAddRec.first);