[PATCH] D13740: Catch combine opportunities for redundant imuls

[Zia Ansari via llvm-commits]

zansari created this revision.
zansari added reviewers: mkuper, delena, spatel, hfinkel.
zansari added a subscriber: llvm-commits.

When we fold (mul (add x, c1), c1) -> (add (mul x, c2), c1*c2), we bail if (add x, c1) has multiple users, leaving and extra add instruction. In such cases, this patch adds a check to see if we can eliminate a multiply instruction in exchange for the extra add. combine-multiplies.ll illustrates this issue in a little more detail.

http://reviews.llvm.org/D13740

Files:
  lib/CodeGen/SelectionDAG/DAGCombiner.cpp
  test/CodeGen/X86/combine-multiplies.ll

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