[Mlir-commits] [mlir] [mlir] Optimize const values AffineMap::compose (PR #141005)

[Jeremy Kun]

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@@ -579,16 +579,16 @@ AffineMap AffineMap::compose(AffineMap map) const {
 
 SmallVector<int64_t, 4> AffineMap::compose(ArrayRef<int64_t> values) const {
   assert(getNumSymbols() == 0 && "Expected symbol-less map");
-  SmallVector<AffineExpr, 4> exprs;
-  exprs.reserve(values.size());
+  unsigned numValues = values.size();
+  DenseMap<AffineExpr, AffineExpr> mapping;
   MLIRContext *ctx = getContext();
-  for (auto v : values)
-    exprs.push_back(getAffineConstantExpr(v, ctx));
-  auto resMap = compose(AffineMap::get(0, 0, exprs, ctx));
+  for (unsigned idx = 0; idx < numValues; ++idx)
+    mapping[getAffineDimExpr(idx, ctx)] =
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j2kun wrote:

Since you know you're replacing dims directly and it's not a sparse replacement (every dim is replaced), why not use `replaceDims`/`replaceDimsAndSymbols`? This avoids constructing the `getAffineDimExpr` as well as avoiding the hashmap construction/lookups (in favor of array indexing which is more performant).

https://github.com/llvm/llvm-project/pull/141005