[llvm] [WebAssembly] [Backend] Wasm optimize illegal bitmask (PR #145627)

[Sam Parker via llvm-commits]

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@@ -3236,6 +3244,57 @@ static SDValue performBitcastCombine(SDNode *N,
         DL, VT);
   }
 
+  // bitcast <N x i1>(setcc ...) to concat iN, where N = 32 and 64 (illegal)
+  if (NumElts == 32 || NumElts == 64) {
+    // Strategy: We will setcc them seperately in v16i1
+    // Bitcast them to i16, extend them to either i32 or i64.
+    // Add them together, shifting left 1 by 1.
+    SDValue Concat, SetCCVector;
+    ISD::CondCode SetCond;
+
+    if (!sd_match(N, m_BitCast(m_c_SetCC(m_Value(Concat),
+                                         m_VectorVT(m_Value(SetCCVector)),
+                                         m_CondCode(SetCond)))))
+      return SDValue();
+    // COMMITTED at this point, SDValue() if match fails.
+    if (Concat.getOpcode() != ISD::CONCAT_VECTORS)
+      return SDValue();
+    // CHECK IF VECTOR is a constant, i.e all values are the same
+    if (!ISD::isBuildVectorOfConstantSDNodes(SetCCVector.getNode()))
+      return SDValue();
+
+    SmallVector<SDValue> Vec;
+    for (SDValue Const : SetCCVector->ops()) {
+      Vec.push_back(Const);
+      if (Vec.size() >= 16)
+        break;
+    }
+
+    // Build our own version of splat Vector.
+    SDValue SplitSetCCVec = DAG.getBuildVector(MVT::v16i8, DL, Vec);
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sparker-arm wrote:

Or just take the constant value and `SPLAT` it?

https://github.com/llvm/llvm-project/pull/145627