[SimplifyCFG] don't sink common insts too soon (PR34603)

This should solve:
https://bugs.llvm.org/show_bug.cgi?id=34603
...by preventing SimplifyCFG from altering redundant instructions before early-cse has a chance to run.
It changes the default (canonical-forming) behavior of SimplifyCFG, so we're only doing the
sinking transform later in the optimization pipeline.

Differential Revision: https://reviews.llvm.org/D38566

llvm-svn: 320749

1 files changed, 15 insertions, 1 deletions

diff --git a/llvm/lib/Transforms/Scalar/SimplifyCFGPass.cpp b/llvm/lib/Transforms/Scalar/SimplifyCFGPass.cpp
index 789e0a4..1522170 100644
--- a/llvm/lib/Transforms/Scalar/SimplifyCFGPass.cpp
+++ b/llvm/lib/Transforms/Scalar/SimplifyCFGPass.cpp
@@ -61,6 +61,11 @@ static cl::opt<bool> UserForwardSwitchCond(
     "forward-switch-cond", cl::Hidden, cl::init(false),
     cl::desc("Forward switch condition to phi ops (default = false)"));
 
+static cl::opt<bool> UserSinkCommonInsts(
+    "sink-common-insts", cl::Hidden, cl::init(false),
+    cl::desc("Sink common instructions (default = false)"));
+
+
 STATISTIC(NumSimpl, "Number of blocks simplified");
 
 /// If we have more than one empty (other than phi node) return blocks,
@@ -205,6 +210,9 @@ SimplifyCFGPass::SimplifyCFGPass(const SimplifyCFGOptions &Opts) {
   Options.NeedCanonicalLoop = UserKeepLoops.getNumOccurrences()
                                   ? UserKeepLoops
                                   : Opts.NeedCanonicalLoop;
+  Options.SinkCommonInsts = UserSinkCommonInsts.getNumOccurrences()
+                                ? UserSinkCommonInsts
+                                : Opts.SinkCommonInsts;
 }
 
 PreservedAnalyses SimplifyCFGPass::run(Function &F,
@@ -226,6 +234,7 @@ struct CFGSimplifyPass : public FunctionPass {
 
   CFGSimplifyPass(unsigned Threshold = 1, bool ForwardSwitchCond = false,
                   bool ConvertSwitch = false, bool KeepLoops = true,
+                  bool SinkCommon = false,
                   std::function<bool(const Function &)> Ftor = nullptr)
       : FunctionPass(ID), PredicateFtor(std::move(Ftor)) {
 
@@ -246,6 +255,10 @@ struct CFGSimplifyPass : public FunctionPass {
 
     Options.NeedCanonicalLoop =
         UserKeepLoops.getNumOccurrences() ? UserKeepLoops : KeepLoops;
+
+    Options.SinkCommonInsts = UserSinkCommonInsts.getNumOccurrences()
+                                  ? UserSinkCommonInsts
+                                  : SinkCommon;
   }
 
   bool runOnFunction(Function &F) override {
@@ -276,7 +289,8 @@ INITIALIZE_PASS_END(CFGSimplifyPass, "simplifycfg", "Simplify the CFG", false,
 FunctionPass *
 llvm::createCFGSimplificationPass(unsigned Threshold, bool ForwardSwitchCond,
                                   bool ConvertSwitch, bool KeepLoops,
+                                  bool SinkCommon,
                                   std::function<bool(const Function &)> Ftor) {
   return new CFGSimplifyPass(Threshold, ForwardSwitchCond, ConvertSwitch,
-                             KeepLoops, std::move(Ftor));
+                             KeepLoops, SinkCommon, std::move(Ftor));
 }