[llvm] [RISCV][GISel] Added GISelPRedicateCodes to LeadingOnes*Mask (PR #119886)

[Craig Topper via llvm-commits]

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@@ -493,7 +493,15 @@ def LeadingOnesMask : PatLeaf<(imm), [{
   if (!N->hasOneUse())
     return false;
   return !isInt<32>(N->getSExtValue()) && isMask_64(~N->getSExtValue());
-}], TrailingZeros>;
+}], TrailingZeros> {
+  let GISelPredicateCode = [{
+    if (!MRI.hasOneNonDBGUse(MI.getOperand(0).getReg()))
+      return false;
+    const auto &MO = MI.getOperand(1);
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topperc wrote:

GISel uses MachineIR where defs and uses are "operands". For G_CONSTANT, operand 0 is the def and operand 1 is the source.

SelectionDAG operands are only inputs. Results are separate.

The `(imm)` in the PatLeaf should guarantee this is only called for G_CONSTANT.

https://github.com/llvm/llvm-project/pull/119886