[PATCH] D37888: [SCEV] Generalize folding of trunc(x)+n*trunc(y) into folding m*trunc(x)+n*trunc(y)

[Sanjoy Das via Phabricator via llvm-commits]

sanjoy requested changes to this revision.
sanjoy added inline comments.
This revision now requires changes to proceed.


================
Comment at: lib/Analysis/ScalarEvolution.cpp:2347
+    for (unsigned i=Idx; i<Ops.size() && Ops[i]->getSCEVType() <= scMulExpr; ++i) {
+      if (isa<SCEVTruncateExpr>(Ops[i])) {
+        return cast<SCEVTruncateExpr>(Ops[i]);
----------------
This is doing a bit more work than it needs to -- if the first element after a constant isn't a trunc, then none of them are.


================
Comment at: lib/Analysis/ScalarEvolution.cpp:2366
+  };
+  if (const auto *Trunc = FindTrunc()) {
     Type *DstType = Trunc->getType();
----------------
Instead of searching from a trunc operation and going from there, how about phrasing this logic as:

  1. First figure out the SrcType, if possible (by looking at truncates and multiplies)
  2. If (1) was successful, re-traverse the operands and try to do the trunc extraction

This makes it clear that the second part is only using SrcType and not the whole truncate.


https://reviews.llvm.org/D37888