[llvm] Add more cases for computeOverflowForSignedAdd (PR #99900)

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``````````bash
git-clang-format --diff 1c798e0b077f062dbe56603021a9b67c7621ffe0 4072ffa1aee863e6614a8eab2804b2d8dbfc17c9 --extensions cpp -- llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
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View the diff from clang-format here.
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``````````diff
diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
index 9cec62a3be..e060ec6474 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
@@ -4241,8 +4241,8 @@ SelectionDAG::computeOverflowForSignedAdd(SDValue N0, SDValue N1) const {
   // cannot overflow.
   if (ComputeNumSignBits(N0) > 1 && ComputeNumSignBits(N1) > 1)
     return OFK_Never;
-  
-    // smulhi + any value never overflow
+
+  // smulhi + any value never overflow
   KnownBits N1Known = computeKnownBits(N1);
   if (N0.getOpcode() == ISD::SMUL_LOHI && N0.getResNo() == 1)
     return OFK_Never;
@@ -4250,8 +4250,8 @@ SelectionDAG::computeOverflowForSignedAdd(SDValue N0, SDValue N1) const {
   KnownBits N0Known = computeKnownBits(N0);
   if (N1.getOpcode() == ISD::SMUL_LOHI && N1.getResNo() == 1)
     return OFK_Never;
-  
-    // Fallback to ConstantRange::signedAddMayOverflow handling.
+
+  // Fallback to ConstantRange::signedAddMayOverflow handling.
   ConstantRange N0Range = ConstantRange::fromKnownBits(N0Known, false);
   ConstantRange N1Range = ConstantRange::fromKnownBits(N1Known, false);
   return mapOverflowResult(N0Range.signedAddMayOverflow(N1Range));

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https://github.com/llvm/llvm-project/pull/99900