[llvm] [AMDGPU][SDAG] Legalise v2i32 or/xor/and instructions to make use of 64-bit wide instructions (PR #140694)

[Janek van Oirschot via llvm-commits]

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@@ -12872,6 +12887,46 @@ SDValue SITargetLowering::performOrCombine(SDNode *N,
     }
   }
 
+  // Detect identity v2i32 OR and replace with identity source node.
+  // Specifically an Or that has operands constructed from the same source node
+  // via extract_vector_elt and build_vector.
+  if (VT == MVT::v2i32) {
+    if (LHS->getOpcode() == ISD::BUILD_VECTOR &&
+        RHS->getOpcode() == ISD::BUILD_VECTOR) {
+      LLVM_DEBUG(dbgs() << "### Performing v2i32 SIISelLowering "
+                           "DAGCombine::CombineOR\n";);
+
+      auto *LC = dyn_cast<ConstantSDNode>(LHS->getOperand(1));
+      auto *RC = dyn_cast<ConstantSDNode>(RHS->getOperand(0));
+
+      if (LC && RC) {
+
+        // Test for and normalise build vectors.
+        if (LHS->getOpcode() == ISD::BUILD_VECTOR &&
+            RHS->getOpcode() == ISD::BUILD_VECTOR &&
+            // Check cast to constantnode here
+            LHS->getConstantOperandVal(1) == 0 &&
+            RHS->getConstantOperandVal(0) == 0) {
+
+          // Get the extract_vector_element operands.
+          SDValue LEVE = LHS->getOperand(0);
+          SDValue REVE = RHS->getOperand(1);
+
+          if (LEVE->getOpcode() == ISD::EXTRACT_VECTOR_ELT &&
+              REVE->getOpcode() == ISD::EXTRACT_VECTOR_ELT) {
+            // Check that the the elements from the same vector are extracted.
+            if (LEVE->getOperand(0) == REVE->getOperand(0) &&
+                LEVE->getOperand(1) != REVE->getOperand(1)) {
+              LLVM_DEBUG(dbgs() << "### Found identity OR, folding...\n";);
+              SDValue IdentitySrc = LEVE.getOperand(0);
+              return IdentitySrc;
+            }
+          }
+        }
+      }
+    }
+  }
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JanekvO wrote:

Quite the nest of if-statements. Is it possible to perhaps combine the condition into its own static function/lambda? Or perhaps combine some ifs to reduce this nest?

https://github.com/llvm/llvm-project/pull/140694