From b80daf0b48c6be27812c95904298fac0c9bdc4e2 Mon Sep 17 00:00:00 2001
From: Sanjay Patel <spatel@rotateright.com>
Date: Sun, 22 Oct 2017 19:10:07 +0000
Subject: [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.

llvm-svn: 316298
---
 llvm/lib/Transforms/Scalar/SimplifyCFGPass.cpp | 18 ++++++++++++------
 1 file changed, 12 insertions(+), 6 deletions(-)

(limited to 'llvm/lib/Transforms/Scalar/SimplifyCFGPass.cpp')

diff --git a/llvm/lib/Transforms/Scalar/SimplifyCFGPass.cpp b/llvm/lib/Transforms/Scalar/SimplifyCFGPass.cpp
index 723619f46bb..6f38e5d11b5 100644
--- a/llvm/lib/Transforms/Scalar/SimplifyCFGPass.cpp
+++ b/llvm/lib/Transforms/Scalar/SimplifyCFGPass.cpp
@@ -179,8 +179,10 @@ static bool simplifyFunctionCFG(Function &F, const TargetTransformInfo &TTI,
   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 FunctionPass {
     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 BaseCFGSimplifyPass {
 
   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 BaseCFGSimplifyPass {
 
   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());
   }
 };
-- 
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