[PATCH] D124374: [RISCV][TargetLowering] Special case overflow expansion for (uaddo X, C).

[Craig Topper via Phabricator via llvm-commits]

craig.topper added inline comments.


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Comment at: llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp:8826
     // the live range of X. We assume comparing with 0 is cheap.
-    // TODO: This generalizes to (X + C) < C.
+    // The general case (X + C) < C is not necessary benefits. Although we
+    // reduce the live range of X, we may introduce the materialization of
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"necessary benefits" -> "necessarily beneficial"


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Comment at: llvm/lib/Target/RISCV/RISCVISelLowering.cpp:6974
       // Special case uaddo X, 1 overflowed if the addition result is 0.
-      // FIXME: We can do this for any constant RHS by using (X + C) < C.
+      // The general case (X + C) < C is not necessary benefits. Although we
+      // reduce the live range of X, we may introduce the materialization of
----------------
Here too


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Comment at: llvm/lib/Target/RISCV/RISCVISelLowering.cpp:6976
+      // reduce the live range of X, we may introduce the materialization of
+      // constant C, especially the setcc result is used by branch. We have no
+      // compare with constant and branch instructions.
----------------
"especially the setcc" -> "especially when the setcc"


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  https://reviews.llvm.org/D124374/new/

https://reviews.llvm.org/D124374