[flang-commits] [flang] [flang] Inline hlfir.reshape as hlfir.elemental. (PR #124683)

[Slava Zakharin via flang-commits]

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@@ -951,6 +951,213 @@ class DotProductConversion
   }
 };
 
+class ReshapeAsElementalConversion
+    : public mlir::OpRewritePattern<hlfir::ReshapeOp> {
+public:
+  using mlir::OpRewritePattern<hlfir::ReshapeOp>::OpRewritePattern;
+
+  llvm::LogicalResult
+  matchAndRewrite(hlfir::ReshapeOp reshape,
+                  mlir::PatternRewriter &rewriter) const override {
+    // Do not inline RESHAPE with ORDER yet. The runtime implementation
+    // may be good enough, unless the temporary creation overhead
+    // is high.
+    // TODO: If ORDER is constant, then we can still easily inline.
+    // TODO: If the result's rank is 1, then we can assume ORDER == (/1/).
+    if (reshape.getOrder())
+      return rewriter.notifyMatchFailure(reshape,
+                                         "RESHAPE with ORDER argument");
+
+    // Verify that the element types of ARRAY, PAD and the result
+    // match before doing any transformations.
+    hlfir::Entity result = hlfir::Entity{reshape};
+    hlfir::Entity array = hlfir::Entity{reshape.getArray()};
+    mlir::Type elementType = array.getFortranElementType();
+    if (result.getFortranElementType() != elementType)
+      return rewriter.notifyMatchFailure(
+          reshape, "ARRAY and result have different types");
+    mlir::Value pad = reshape.getPad();
+    if (pad && hlfir::getFortranElementType(pad.getType()) != elementType)
+      return rewriter.notifyMatchFailure(reshape,
+                                         "ARRAY and PAD have different types");
+
+    // TODO: selecting between ARRAY and PAD of non-trivial element types
+    // requires more work. We have to select between two references
+    // to elements in ARRAY and PAD. This requires conditional
+    // bufferization of the element, if ARRAY/PAD is an expression.
+    if (pad && !fir::isa_trivial(elementType))
+      return rewriter.notifyMatchFailure(reshape,
+                                         "PAD present with non-trivial type");
+
+    mlir::Location loc = reshape.getLoc();
+    fir::FirOpBuilder builder{rewriter, reshape.getOperation()};
+    // Assume that all the indices arithmetic does not overflow
+    // the IndexType.
+    builder.setIntegerOverflowFlags(mlir::arith::IntegerOverflowFlags::nuw);
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vzakhari wrote:

I am using unsigned arithmetic. `-fwrapv` does not quite fit, so I am not sure.

https://github.com/llvm/llvm-project/pull/124683