[PATCH] D131471: [RISCV] Fold (sub constant, (setcc x, y, eq/neq)) -> (add constant - 1, (setcc x, y, neq/eq))

[Craig Topper via Phabricator via llvm-commits]

craig.topper added inline comments.


================
Comment at: llvm/lib/Target/RISCV/RISCVISelLowering.cpp:8276
+  if (isa<ConstantSDNode>(N0) && N1.getOpcode() == ISD::SETCC &&
+      N->isOnlyUserOf(N1.getNode())) {
+    auto *Nnz0 = cast<ConstantSDNode>(N0);
----------------
You can use `N1.hasOneUse()` which should be cheaper. `isOnlyUser` is more useful if N had multiple operands that could each be N1. We know one operand of N is a constant so N1 can only be used by one operand.


================
Comment at: llvm/lib/Target/RISCV/RISCVISelLowering.cpp:8282
+      EVT VT = N->getValueType(0);
+      int64_t ImmVal = cast<ConstantSDNode>(N0)->getSExtValue() - 1;
+      SDValue CCInverse =
----------------
This line has undefined behavior if N0 happens to be 0x8000000000000000.

It's also incorrect if N is type i65 or larger. Probably best to use APInt which will fix both issues.


Repository:
  rG LLVM Github Monorepo

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  https://reviews.llvm.org/D131471/new/

https://reviews.llvm.org/D131471