[CVP] Handle instructions with no user. No need to create CVPLattice state. This...

Summary:
I tested this patch by compiling sqlite3.ll (clang -O3 -mllvm -disable-llvm-optzns sqlite3.c.)

 opt -called-value-propagation sqlite3.ll -time-passes -f -o out.ll

 I get 10+% speedup for the pass. I expect some of the gain come from skipping terminator instructions.

    === BEFORE THE PATCH ===
    ===-------------------------------------------------------------------------===
                          ... Pass execution timing report ...
    ===-------------------------------------------------------------------------===
      Total Execution Time: 0.5562 seconds (0.5582 wall clock)

       ---User Time---   --System Time--   --User+System--   ---Wall Time---  --- Name ---
       0.2485 ( 46.4%)   0.0120 ( 57.7%)   0.2605 ( 46.8%)   0.2615 ( 46.8%)  Bitcode Writer
       0.1607 ( 30.0%)   0.0079 ( 37.7%)   0.1685 ( 30.3%)   0.1693 ( 30.3%)  Called Value Propagation
       0.1262 ( 23.6%)   0.0009 (  4.5%)   0.1271 ( 22.9%)   0.1275 ( 22.8%)  Module Verifier
       0.5353 (100.0%)   0.0209 (100.0%)   0.5562 (100.0%)   0.5582 (100.0%)  Total

    === AFTER THE PATCH ===
    ===-------------------------------------------------------------------------===
                          ... Pass execution timing report ...
    ===-------------------------------------------------------------------------===
      Total Execution Time: 0.5338 seconds (0.5355 wall clock)

       ---User Time---   --System Time--   --User+System--   ---Wall Time---  --- Name ---
       0.2498 ( 48.6%)   0.0118 ( 59.3%)   0.2615 ( 49.0%)   0.2629 ( 49.1%)  Bitcode Writer
       0.1377 ( 26.8%)   0.0075 ( 37.8%)   0.1452 ( 27.2%)   0.1455 ( 27.2%)  Called Value Propagation
       0.1264 ( 24.6%)   0.0006 (  3.0%)   0.1270 ( 23.8%)   0.1271 ( 23.7%)  Module Verifier
       0.5139 (100.0%)   0.0199 (100.0%)   0.5338 (100.0%)   0.5355 (100.0%)  Total

Reviewers: davide, mssimpso

Reviewed By: davide

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D49108

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@342398 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Transforms/IPO/CalledValuePropagation.cpp b/lib/Transforms/IPO/CalledValuePropagation.cpp
index d642445..de62cfc 100644 (file)
--- a/lib/Transforms/IPO/CalledValuePropagation.cpp
+++ b/lib/Transforms/IPO/CalledValuePropagation.cpp
@@ -345,6 +345,9 @@ private:
   void visitInst(Instruction &I,
                  DenseMap<CVPLatticeKey, CVPLatticeVal> &ChangedValues,
                  SparseSolver<CVPLatticeKey, CVPLatticeVal> &SS) {
+    // Simply bail if this instruction has no user.
+    if (I.use_empty())
+      return;
     auto RegI = CVPLatticeKey(&I, IPOGrouping::Register);
     ChangedValues[RegI] = getOverdefinedVal();
   }