[llvm] [NVPTX] Add support for clamped funnel shift intrinsics (PR #113228)

[Artem Belevich via llvm-commits]

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@@ -384,6 +393,22 @@ static Instruction *simplifyNvvmIntrinsic(IntrinsicInst *II, InstCombiner &IC) {
     return BinaryOperator::Create(
         Instruction::FDiv, ConstantFP::get(II->getArgOperand(0)->getType(), 1),
         II->getArgOperand(0), II->getName());
+
+  case SCP_FunnelShiftClamp: {
+    // Canoncialize a clamping funnel shift to the generic llvm funnel shift
+    // when possible, as this is easier for llvm to optimize further.
+    if (const auto *ShiftConst = dyn_cast<ConstantInt>(II->getArgOperand(2))) {
+      if (ShiftConst->getZExtValue() >= II->getType()->getIntegerBitWidth())
+        return IC.replaceInstUsesWith(*II, II->getArgOperand(1));
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Artem-B wrote:

Unless I'm mistaken, clamped shift right should've returned MSB bits, AKA `getArgOperand(0)`. See the test comment below.

https://github.com/llvm/llvm-project/pull/113228