[PATCH] D83153: [DAGCombiner] Prevent regression in isMulAddWithConstProfitable

[Roman Lebedev via Phabricator via llvm-commits]

lebedev.ri added inline comments.


================
Comment at: llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp:15755-15759
+        // This transform will introduce regression, if c1 is legal add
+        // immediate while c1*c2 isn't.
+        const TargetLowering &TLI = DAG.getTargetLoweringInfo();
+        if (TLI.isLegalAddImmediate(C1) && !TLI.isLegalAddImmediate(C1C2))
+          return false;
----------------
You also need a second piece if the puzzle, because we would have
already performed this transform before ever getting here:
https://godbolt.org/z/TE_bzk

You need to add an inverse transform into DAGCombiner.cpp.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D83153/new/

https://reviews.llvm.org/D83153