[mlir][vector] Add folder for bitcast of integer splat constants

[qedawkins]

Summary

This is a similar to the existing folder for f16 to f32 added with D96041 but instead for integer types where destination bits > source bits.

[ThomasRaoux]

mlir/lib/Dialect/Vector/IR/VectorOps.cpp

4953

optional comment but it should be easy to generalize to any integer size using APInt.

[qedawkins]

Generalize pattern to arbitrary bit widths

[qedawkins]

add back initial commit

[qedawkins]

mlir/lib/Dialect/Vector/IR/VectorOps.cpp

4953

Amended to generalize to integer sizes where destination bit width > source bit width.

[ThomasRaoux]

Nice :) Thanks! Make sure to update the title and description.

mlir/lib/Dialect/Vector/IR/VectorOps.cpp

if (floatPack.isSplat()) {
       }
     }
   }
 
   if (auto intPack = sourceConstant.dyn_cast<DenseIntElementsAttr>()) {
     if (intPack.isSplat()) {
       auto splat = intPack.getSplatValue<IntegerAttr>();
 
-      // Casting int8 into int32.
-      if (srcElemType.isInteger(8) && dstElemType.isInteger(32)) {
-        uint32_t bits = static_cast<uint32_t>(splat.getValue().getZExtValue());
-        // Duplicate the 8-bit pattern.
-        bits = (bits << 24) | (bits << 16) | (bits << 8) | bits;
-        APInt intBits(32, bits);
+      if (dstElemType.isa<IntegerType>()) {
+        uint64_t srcBitWidth = srcElemType.getIntOrFloatBitWidth();
+        uint64_t dstBitWidth = dstElemType.getIntOrFloatBitWidth();
+
+        // Casting to a larger integer bit width.
+        if (dstBitWidth > srcBitWidth && dstBitWidth % srcBitWidth == 0) {
+          APInt intBits = splat.getValue().zext(dstBitWidth);
+
+          // Duplicate the lower width element.
+          for (uint64_t i = 0; i < dstBitWidth / srcBitWidth - 1; i++)
+            intBits = (intBits << srcBitWidth) | intBits;
           return DenseElementsAttr::get(getResultVectorType(), intBits);
         }
       }
     }
+  }
 
   return {};
 }
 
 //===----------------------------------------------------------------------===//
 // TypeCastOp
 //===----------------------------------------------------------------------===//