[llvm] r316298 - [SimplifyCFG] delay switch condition forwarding to -latesimplifycfg

[Sanjay Patel via llvm-commits]

Author: spatel
Date: Sun Oct 22 12:10:07 2017
New Revision: 316298

URL: http://llvm.org/viewvc/llvm-project?rev=316298&view=rev
Log:
[SimplifyCFG] delay switch condition forwarding to -latesimplifycfg

As discussed in D39011:
https://reviews.llvm.org/D39011
...replacing constants with a variable is inverting the transform done
by other IR passes, so we definitely don't want to do this early. 
In fact, it's questionable whether this transform belongs in SimplifyCFG 
at all. I'll look at moving this to codegen as a follow-up step.


Modified:
    llvm/trunk/include/llvm/Transforms/Utils/Local.h
    llvm/trunk/lib/Transforms/Scalar/SimplifyCFGPass.cpp
    llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp
    llvm/trunk/test/Transforms/SimplifyCFG/ForwardSwitchConditionToPHI.ll

Modified: llvm/trunk/include/llvm/Transforms/Utils/Local.h
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/Transforms/Utils/Local.h?rev=316298&r1=316297&r2=316298&view=diff
==============================================================================
--- llvm/trunk/include/llvm/Transforms/Utils/Local.h (original)
+++ llvm/trunk/include/llvm/Transforms/Utils/Local.h Sun Oct 22 12:10:07 2017
@@ -60,14 +60,16 @@ class TargetTransformInfo;
 /// replaced by lookup tables and selects.
 struct SimplifyCFGOptions {
   int BonusInstThreshold;
+  bool ForwardSwitchCondToPhi;
   bool ConvertSwitchToLookupTable;
   bool NeedCanonicalLoop;
   AssumptionCache *AC;
 
-  SimplifyCFGOptions(int BonusThreshold = 1, bool SwitchToLookup = false,
-                     bool CanonicalLoops = true,
+  SimplifyCFGOptions(int BonusThreshold = 1, bool ForwardSwitchCond = false,
+                     bool SwitchToLookup = false, bool CanonicalLoops = true,
                      AssumptionCache *AssumpCache = nullptr)
       : BonusInstThreshold(BonusThreshold),
+        ForwardSwitchCondToPhi(ForwardSwitchCond),
         ConvertSwitchToLookupTable(SwitchToLookup),
         NeedCanonicalLoop(CanonicalLoops), AC(AssumpCache) {}
 };

Modified: llvm/trunk/lib/Transforms/Scalar/SimplifyCFGPass.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/SimplifyCFGPass.cpp?rev=316298&r1=316297&r2=316298&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Scalar/SimplifyCFGPass.cpp (original)
+++ llvm/trunk/lib/Transforms/Scalar/SimplifyCFGPass.cpp Sun Oct 22 12:10:07 2017
@@ -179,8 +179,10 @@ static bool simplifyFunctionCFG(Function
   return true;
 }
 
+// FIXME: The new pass manager always creates a "late" simplifycfg pass using
+// this default constructor.
 SimplifyCFGPass::SimplifyCFGPass()
-    : Options(UserBonusInstThreshold, true, false) {}
+    : Options(UserBonusInstThreshold, true, true, false) {}
 
 SimplifyCFGPass::SimplifyCFGPass(const SimplifyCFGOptions &PassOptions)
     : Options(PassOptions) {}
@@ -200,12 +202,15 @@ namespace {
 struct BaseCFGSimplifyPass : public FunctionPass {
   std::function<bool(const Function &)> PredicateFtor;
   int BonusInstThreshold;
+  bool ForwardSwitchCondToPhi;
   bool ConvertSwitchToLookupTable;
   bool KeepCanonicalLoops;
 
-  BaseCFGSimplifyPass(int T, bool ConvertSwitch, bool KeepLoops,
+  BaseCFGSimplifyPass(int T, bool ForwardSwitchCond, bool ConvertSwitch,
+                      bool KeepLoops,
                       std::function<bool(const Function &)> Ftor, char &ID)
       : FunctionPass(ID), PredicateFtor(std::move(Ftor)),
+        ForwardSwitchCondToPhi(ForwardSwitchCond),
         ConvertSwitchToLookupTable(ConvertSwitch),
         KeepCanonicalLoops(KeepLoops) {
     BonusInstThreshold = (T == -1) ? UserBonusInstThreshold : T;
@@ -219,8 +224,9 @@ struct BaseCFGSimplifyPass : public Func
     const TargetTransformInfo &TTI =
         getAnalysis<TargetTransformInfoWrapperPass>().getTTI(F);
     return simplifyFunctionCFG(F, TTI,
-                               {BonusInstThreshold, ConvertSwitchToLookupTable,
-                                KeepCanonicalLoops, AC});
+                               {BonusInstThreshold, ForwardSwitchCondToPhi,
+                                ConvertSwitchToLookupTable, KeepCanonicalLoops,
+                                AC});
   }
 
   void getAnalysisUsage(AnalysisUsage &AU) const override {
@@ -235,7 +241,7 @@ struct CFGSimplifyPass : public BaseCFGS
 
   CFGSimplifyPass(int T = -1,
                   std::function<bool(const Function &)> Ftor = nullptr)
-                  : BaseCFGSimplifyPass(T, false, true, Ftor, ID) {
+                  : BaseCFGSimplifyPass(T, false, false, true, Ftor, ID) {
     initializeCFGSimplifyPassPass(*PassRegistry::getPassRegistry());
   }
 };
@@ -245,7 +251,7 @@ struct LateCFGSimplifyPass : public Base
 
   LateCFGSimplifyPass(int T = -1,
                       std::function<bool(const Function &)> Ftor = nullptr)
-                      : BaseCFGSimplifyPass(T, true, false, Ftor, ID) {
+                      : BaseCFGSimplifyPass(T, true, true, false, Ftor, ID) {
     initializeLateCFGSimplifyPassPass(*PassRegistry::getPassRegistry());
   }
 };

Modified: llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp?rev=316298&r1=316297&r2=316298&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp (original)
+++ llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp Sun Oct 22 12:10:07 2017
@@ -5563,7 +5563,7 @@ bool SimplifyCFGOpt::SimplifySwitch(Swit
   if (switchToSelect(SI, Builder, DL, TTI))
     return simplifyCFG(BB, TTI, Options) | true;
 
-  if (ForwardSwitchConditionToPHI(SI))
+  if (Options.ForwardSwitchCondToPhi && ForwardSwitchConditionToPHI(SI))
     return simplifyCFG(BB, TTI, Options) | true;
 
   // The conversion from switch to lookup tables results in difficult-to-analyze

Modified: llvm/trunk/test/Transforms/SimplifyCFG/ForwardSwitchConditionToPHI.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/SimplifyCFG/ForwardSwitchConditionToPHI.ll?rev=316298&r1=316297&r2=316298&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/SimplifyCFG/ForwardSwitchConditionToPHI.ll (original)
+++ llvm/trunk/test/Transforms/SimplifyCFG/ForwardSwitchConditionToPHI.ll Sun Oct 22 12:10:07 2017
@@ -1,5 +1,5 @@
 ; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
-; RUN: opt < %s -simplifycfg -S | FileCheck %s
+; RUN: opt < %s -latesimplifycfg -S | FileCheck %s
 
 ; PR10131