[PATCH] D86347: [SimplifyCFG] Two entry phi select costs

[Sam Parker via Phabricator via llvm-commits]

samparker added inline comments.


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Comment at: llvm/lib/Transforms/Utils/SimplifyCFG.cpp:98-102
 static cl::opt<unsigned> TwoEntryPHINodeFoldingThreshold(
     "two-entry-phi-node-folding-threshold", cl::Hidden, cl::init(4),
     cl::desc("Control the maximal total instruction cost that we are willing "
              "to speculatively execute to fold a 2-entry PHI node into a "
              "select (default = 4)"));
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lebedev.ri wrote:
> You need to bump it by that new cmp+sel cost, so `+2`.
Where is the cmp coming from?


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Comment at: llvm/lib/Transforms/Utils/SimplifyCFG.cpp:2011
+    if (OrigV != ThenV)
+      BudgetRemaining -=
+          TTI.getCmpSelInstrCost(Instruction::Select, PN.getType(), nullptr,
----------------
lebedev.ri wrote:
> I'm not sure this does what you think it does..
Do you think this is wrong? What do you think it should be doing?


Repository:
  rG LLVM Github Monorepo

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  https://reviews.llvm.org/D86347/new/

https://reviews.llvm.org/D86347