[mlir][Vector] Update VectorEmulateNarrowType.cpp (2/N)

This is PR 2 in a series of N patches aimed at improving
"VectorEmulateNarrowType.cpp". This is mainly minor refactoring, no
major functional changes are made/added.

This PR renames the variable "scale". Note, "scale" could mean either:

  * "original-elements-per-emulated-type", or
  * "emulated-elements-per-original-type".

While from the context it is clear that it's always the former (original
type is always a sub-byte type and the emulated type is usually `i8`),
this PR reduces the cognitive load by making this clear.

**DEPENDS ON:**
* #123526 123526

Please only review the [top
commit](d40b31b).

**GitHub issue to track this work**:
#123630

Author: banach-space

mlir/lib/Dialect/Vector/Transforms/VectorEmulateNarrowType.cpp

@@ -290,13 +290,15 @@ static VectorValue emulatedVectorLoad(OpBuilder &rewriter, Location loc,
                                       int64_t numContainerElemsToLoad,
                                       Type emulatedElemTy,
                                       Type containerElemTy) {
-  auto scale = containerElemTy.getIntOrFloatBitWidth() /
-               emulatedElemTy.getIntOrFloatBitWidth();
+  auto emulatedPerContainerElem = containerElemTy.getIntOrFloatBitWidth() /
+                                  emulatedElemTy.getIntOrFloatBitWidth();
   auto newLoad = rewriter.create<vector::LoadOp>(
       loc, VectorType::get(numContainerElemsToLoad, containerElemTy), base,
       getValueOrCreateConstantIndexOp(rewriter, loc, linearizedIndices));
   return rewriter.create<vector::BitCastOp>(
-      loc, VectorType::get(numContainerElemsToLoad * scale, emulatedElemTy),
+      loc,
+      VectorType::get(numContainerElemsToLoad * emulatedPerContainerElem,
+                      emulatedElemTy),
       newLoad);
 }
 
@@ -388,10 +390,11 @@ static Value extractSliceIntoByte(ConversionPatternRewriter &rewriter,
       "sliceNumElements * vector element size must be less than or equal to 8");
   assert(8 % vectorElementType.getIntOrFloatBitWidth() == 0 &&
          "vector element must be a valid sub-byte type");
-  auto scale = 8 / vectorElementType.getIntOrFloatBitWidth();
+  auto emulatedPerContainerElem = 8 / vectorElementType.getIntOrFloatBitWidth();
   auto emptyByteVector = rewriter.create<arith::ConstantOp>(
-      loc, VectorType::get({scale}, vectorElementType),
-      rewriter.getZeroAttr(VectorType::get({scale}, vectorElementType)));
+      loc, VectorType::get({emulatedPerContainerElem}, vectorElementType),
+      rewriter.getZeroAttr(
+          VectorType::get({emulatedPerContainerElem}, vectorElementType)));
   auto extracted = staticallyExtractSubvector(rewriter, loc, vector,
                                               extractOffset, sliceNumElements);
   return staticallyInsertSubvector(rewriter, loc, extracted, emptyByteVector,
@@ -656,9 +659,9 @@ struct ConvertVectorMaskedStore final
               "(bit-wise misalignment)");
     }
 
-    int scale = containerBits / emulatedBits;
+    int emulatedPerContainerElem = containerBits / emulatedBits;
     int origElements = op.getValueToStore().getType().getNumElements();
-    if (origElements % scale != 0)
+    if (origElements % emulatedPerContainerElem != 0)
       return failure();
 
     auto stridedMetadata =
@@ -707,12 +710,13 @@ struct ConvertVectorMaskedStore final
     //
     // FIXME: Make an example based on the comment above work (see #115460 for
     // reproducer).
-    FailureOr<Operation *> newMask =
-        getCompressedMaskOp(rewriter, loc, op.getMask(), origElements, scale);
+    FailureOr<Operation *> newMask = getCompressedMaskOp(
+        rewriter, loc, op.getMask(), origElements, emulatedPerContainerElem);
     if (failed(newMask))
       return failure();
 
-    auto numElements = (origElements + scale - 1) / scale;
+    auto numElements = (origElements + emulatedPerContainerElem - 1) /
+                       emulatedPerContainerElem;
     auto newType = VectorType::get(numElements, containerElemTy);
     auto passThru = rewriter.create<arith::ConstantOp>(
         loc, newType, rewriter.getZeroAttr(newType));
@@ -721,7 +725,8 @@ struct ConvertVectorMaskedStore final
         loc, newType, adaptor.getBase(), linearizedIndices,
         newMask.value()->getResult(0), passThru);
 
-    auto newBitCastType = VectorType::get(numElements * scale, emulatedElemTy);
+    auto newBitCastType =
+        VectorType::get(numElements * emulatedPerContainerElem, emulatedElemTy);
     Value valueToStore =
         rewriter.create<vector::BitCastOp>(loc, newBitCastType, newLoad);
     valueToStore = rewriter.create<arith::SelectOp>(
@@ -765,7 +770,7 @@ struct ConvertVectorLoad final : OpConversionPattern<vector::LoadOp> {
           op, "impossible to pack emulated elements into container elements "
               "(bit-wise misalignment)");
     }
-    int scale = containerBits / emulatedBits;
+    int emulatedPerContainerElem = containerBits / emulatedBits;
 
     // Adjust the number of elements to load when emulating narrow types,
     // and then cast back to the original type with vector.bitcast op.
@@ -797,7 +802,7 @@ struct ConvertVectorLoad final : OpConversionPattern<vector::LoadOp> {
     // compile time as they must be constants.
 
     auto origElements = op.getVectorType().getNumElements();
-    bool isAlignedEmulation = origElements % scale == 0;
+    bool isAlignedEmulation = origElements % emulatedPerContainerElem == 0;
 
     auto stridedMetadata =
         rewriter.create<memref::ExtractStridedMetadataOp>(loc, op.getBase());
@@ -818,9 +823,10 @@ struct ConvertVectorLoad final : OpConversionPattern<vector::LoadOp> {
             : getConstantIntValue(linearizedInfo.intraDataOffset);
 
     // Always load enough elements which can cover the original elements.
-    int64_t maxintraDataOffset = foldedIntraVectorOffset.value_or(scale - 1);
-    auto numElements =
-        llvm::divideCeil(maxintraDataOffset + origElements, scale);
+    int64_t maxintraDataOffset =
+        foldedIntraVectorOffset.value_or(emulatedPerContainerElem - 1);
+    auto numElements = llvm::divideCeil(maxintraDataOffset + origElements,
+                                        emulatedPerContainerElem);
     Value result =
         emulatedVectorLoad(rewriter, loc, adaptor.getBase(), linearizedIndices,
                            numElements, emulatedElemTy, containerElemTy);
@@ -870,7 +876,7 @@ struct ConvertVectorMaskedLoad final
           op, "impossible to pack emulated elements into container elements "
               "(bit-wise misalignment)");
     }
-    int scale = containerBits / emulatedBits;
+    int emulatedPerContainerElem = containerBits / emulatedBits;
 
     // Adjust the number of elements to load when emulating narrow types,
     // and then cast back to the original type with vector.bitcast op.
@@ -916,7 +922,7 @@ struct ConvertVectorMaskedLoad final
     // subvector at the proper offset after bit-casting.
     auto origType = op.getVectorType();
     auto origElements = origType.getNumElements();
-    bool isAlignedEmulation = origElements % scale == 0;
+    bool isAlignedEmulation = origElements % emulatedPerContainerElem == 0;
 
     auto stridedMetadata =
         rewriter.create<memref::ExtractStridedMetadataOp>(loc, op.getBase());
@@ -935,18 +941,21 @@ struct ConvertVectorMaskedLoad final
             ? 0
             : getConstantIntValue(linearizedInfo.intraDataOffset);
 
-    int64_t maxIntraDataOffset = foldedIntraVectorOffset.value_or(scale - 1);
-    FailureOr<Operation *> newMask = getCompressedMaskOp(
-        rewriter, loc, op.getMask(), origElements, scale, maxIntraDataOffset);
+    int64_t maxIntraDataOffset =
+        foldedIntraVectorOffset.value_or(emulatedPerContainerElem - 1);
+    FailureOr<Operation *> newMask =
+        getCompressedMaskOp(rewriter, loc, op.getMask(), origElements,
+                            emulatedPerContainerElem, maxIntraDataOffset);
     if (failed(newMask))
       return failure();
 
     Value passthru = op.getPassThru();
 
-    auto numElements =
-        llvm::divideCeil(maxIntraDataOffset + origElements, scale);
+    auto numElements = llvm::divideCeil(maxIntraDataOffset + origElements,
+                                        emulatedPerContainerElem);
     auto loadType = VectorType::get(numElements, containerElemTy);
-    auto newBitcastType = VectorType::get(numElements * scale, emulatedElemTy);
+    auto newBitcastType =
+        VectorType::get(numElements * emulatedPerContainerElem, emulatedElemTy);
 
     auto emptyVector = rewriter.create<arith::ConstantOp>(
         loc, newBitcastType, rewriter.getZeroAttr(newBitcastType));
@@ -973,8 +982,8 @@ struct ConvertVectorMaskedLoad final
         rewriter.create<vector::BitCastOp>(loc, newBitcastType, newLoad);
 
     Value mask = op.getMask();
-    auto newSelectMaskType =
-        VectorType::get(numElements * scale, rewriter.getI1Type());
+    auto newSelectMaskType = VectorType::get(
+        numElements * emulatedPerContainerElem, rewriter.getI1Type());
     // TODO: try to fold if op's mask is constant
     auto emptyMask = rewriter.create<arith::ConstantOp>(
         loc, newSelectMaskType, rewriter.getZeroAttr(newSelectMaskType));
@@ -1033,11 +1042,11 @@ struct ConvertVectorTransferRead final
           op, "impossible to pack emulated elements into container elements "
               "(bit-wise misalignment)");
     }
-    int scale = containerBits / emulatedBits;
+    int emulatedPerContainerElem = containerBits / emulatedBits;
 
     auto origElements = op.getVectorType().getNumElements();
 
-    bool isAlignedEmulation = origElements % scale == 0;
+    bool isAlignedEmulation = origElements % emulatedPerContainerElem == 0;
 
     auto newPadding = rewriter.create<arith::ExtUIOp>(loc, containerElemTy,
                                                       adaptor.getPadding());
@@ -1060,17 +1069,20 @@ struct ConvertVectorTransferRead final
             ? 0
             : getConstantIntValue(linearizedInfo.intraDataOffset);
 
-    int64_t maxIntraDataOffset = foldedIntraVectorOffset.value_or(scale - 1);
-    auto numElements =
-        llvm::divideCeil(maxIntraDataOffset + origElements, scale);
+    int64_t maxIntraDataOffset =
+        foldedIntraVectorOffset.value_or(emulatedPerContainerElem - 1);
+    auto numElements = llvm::divideCeil(maxIntraDataOffset + origElements,
+                                        emulatedPerContainerElem);
 
     auto newRead = rewriter.create<vector::TransferReadOp>(
         loc, VectorType::get(numElements, containerElemTy), adaptor.getSource(),
         getValueOrCreateConstantIndexOp(rewriter, loc, linearizedIndices),
         newPadding);
 
     auto bitCast = rewriter.create<vector::BitCastOp>(
-        loc, VectorType::get(numElements * scale, emulatedElemTy), newRead);
+        loc,
+        VectorType::get(numElements * emulatedPerContainerElem, emulatedElemTy),
+        newRead);
 
     Value result = bitCast->getResult(0);
     if (!foldedIntraVectorOffset) {