[InstCombine] Add option to clean up some assumptions.

Author: fhahn

llvm/include/llvm/Transforms/InstCombine/InstCombine.h

@@ -31,6 +31,7 @@ struct InstCombineOptions {
   // Verify that a fix point has been reached after MaxIterations.
   bool VerifyFixpoint = false;
   unsigned MaxIterations = InstCombineDefaultMaxIterations;
+  bool CleanupAssumptions = false;
 
   InstCombineOptions() = default;
 
@@ -43,6 +44,11 @@ struct InstCombineOptions {
     MaxIterations = Value;
     return *this;
   }
+
+  InstCombineOptions &setCleanupAssumptions(bool Value) {
+    CleanupAssumptions = Value;
+    return *this;
+  }
 };
 
 class InstCombinePass : public PassInfoMixin<InstCombinePass> {

llvm/lib/Passes/PassBuilder.cpp

@@ -915,6 +915,8 @@ Expected<InstCombineOptions> parseInstCombineOptions(StringRef Params) {
                     ParamName).str(),
             inconvertibleErrorCode());
       Result.setMaxIterations((unsigned)MaxIterations.getZExtValue());
+    } else if (ParamName == "cleanup-assumptions") {
+      Result.setCleanupAssumptions(Enable);
     } else {
       return make_error<StringError>(
           formatv("invalid InstCombine pass parameter '{0}' ", ParamName).str(),

llvm/lib/Passes/PassBuilderPipelines.cpp

@@ -1305,7 +1305,8 @@ void PassBuilder::addVectorPasses(OptimizationLevel Level,
     FPM.addPass(LoopLoadEliminationPass());
   }
   // Cleanup after the loop optimization passes.
-  FPM.addPass(InstCombinePass());
+  FPM.addPass(
+      InstCombinePass(InstCombineOptions().setCleanupAssumptions(true)));
 
   if (Level.getSpeedupLevel() > 1 && ExtraVectorizerPasses) {
     ExtraFunctionPassManager<ShouldRunExtraVectorPasses> ExtraPasses;
@@ -1317,7 +1318,8 @@ void PassBuilder::addVectorPasses(OptimizationLevel Level,
     // dead (or speculatable) control flows or more combining opportunities.
     ExtraPasses.addPass(EarlyCSEPass());
     ExtraPasses.addPass(CorrelatedValuePropagationPass());
-    ExtraPasses.addPass(InstCombinePass());
+    ExtraPasses.addPass(
+        InstCombinePass(InstCombineOptions().setCleanupAssumptions(true)));
     LoopPassManager LPM;
     LPM.addPass(LICMPass(PTO.LicmMssaOptCap, PTO.LicmMssaNoAccForPromotionCap,
                          /*AllowSpeculation=*/true));
@@ -1328,7 +1330,8 @@ void PassBuilder::addVectorPasses(OptimizationLevel Level,
                                         /*UseBlockFrequencyInfo=*/true));
     ExtraPasses.addPass(
         SimplifyCFGPass(SimplifyCFGOptions().convertSwitchRangeToICmp(true)));
-    ExtraPasses.addPass(InstCombinePass());
+    ExtraPasses.addPass(
+        InstCombinePass(InstCombineOptions().setCleanupAssumptions(true)));
     FPM.addPass(std::move(ExtraPasses));
   }
 
@@ -1351,7 +1354,8 @@ void PassBuilder::addVectorPasses(OptimizationLevel Level,
 
   if (IsFullLTO) {
     FPM.addPass(SCCPPass());
-    FPM.addPass(InstCombinePass());
+    FPM.addPass(
+        InstCombinePass(InstCombineOptions().setCleanupAssumptions(true)));
     FPM.addPass(BDCEPass());
   }
 
@@ -1366,7 +1370,8 @@ void PassBuilder::addVectorPasses(OptimizationLevel Level,
   FPM.addPass(VectorCombinePass());
 
   if (!IsFullLTO) {
-    FPM.addPass(InstCombinePass());
+    FPM.addPass(
+        InstCombinePass(InstCombineOptions().setCleanupAssumptions(true)));
     // Unroll small loops to hide loop backedge latency and saturate any
     // parallel execution resources of an out-of-order processor. We also then
     // need to clean up redundancies and loop invariant code.
@@ -1392,7 +1397,8 @@ void PassBuilder::addVectorPasses(OptimizationLevel Level,
   }
 
   FPM.addPass(InferAlignmentPass());
-  FPM.addPass(InstCombinePass());
+  FPM.addPass(
+      InstCombinePass(InstCombineOptions().setCleanupAssumptions(true)));
 
   // This is needed for two reasons:
   //   1. It works around problems that instcombine introduces, such as sinking

llvm/lib/Passes/PassRegistry.def

@@ -540,7 +540,7 @@ FUNCTION_PASS_WITH_PARAMS(
     [](InstCombineOptions Opts) { return InstCombinePass(Opts); },
     parseInstCombineOptions,
     "no-use-loop-info;use-loop-info;no-verify-fixpoint;verify-fixpoint;"
-    "max-iterations=N")
+    "max-iterations=N;cleanup-assumptions")
 FUNCTION_PASS_WITH_PARAMS(
     "loop-unroll", "LoopUnrollPass",
     [](LoopUnrollOptions Opts) { return LoopUnrollPass(Opts); },

llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp

@@ -3172,6 +3172,13 @@ Instruction *InstCombinerImpl::visitCallInst(CallInst &CI) {
         MaybeSimplifyHint(OBU.Inputs[0]);
         MaybeSimplifyHint(OBU.Inputs[1]);
       }
+
+      // Try to clean up some assumption that are not very useful after this
+      // point.
+      if (CleanupAssumptions && OBU.getTagName() == "dereferenceable") {
+        auto *New = CallBase::removeOperandBundle(II, OBU.getTagID());
+        return New;
+      }
     }
 
     // Convert nonnull assume like:

llvm/lib/Transforms/InstCombine/InstCombineInternal.h

@@ -59,16 +59,20 @@ class User;
 class LLVM_LIBRARY_VISIBILITY InstCombinerImpl final
     : public InstCombiner,
       public InstVisitor<InstCombinerImpl, Instruction *> {
+  bool CleanupAssumptions = false;
+
 public:
   InstCombinerImpl(InstructionWorklist &Worklist, BuilderTy &Builder,
                    bool MinimizeSize, AAResults *AA, AssumptionCache &AC,
                    TargetLibraryInfo &TLI, TargetTransformInfo &TTI,
                    DominatorTree &DT, OptimizationRemarkEmitter &ORE,
                    BlockFrequencyInfo *BFI, BranchProbabilityInfo *BPI,
                    ProfileSummaryInfo *PSI, const DataLayout &DL,
-                   ReversePostOrderTraversal<BasicBlock *> &RPOT)
+                   ReversePostOrderTraversal<BasicBlock *> &RPOT,
+                   bool CleanupAssumptions)
       : InstCombiner(Worklist, Builder, MinimizeSize, AA, AC, TLI, TTI, DT, ORE,
-                     BFI, BPI, PSI, DL, RPOT) {}
+                     BFI, BPI, PSI, DL, RPOT),
+        CleanupAssumptions(CleanupAssumptions) {}
 
   virtual ~InstCombinerImpl() = default;
 

llvm/lib/Transforms/InstCombine/InstructionCombining.cpp

@@ -5524,7 +5524,7 @@ static bool combineInstructionsOverFunction(
                       << F.getName() << "\n");
 
     InstCombinerImpl IC(Worklist, Builder, F.hasMinSize(), AA, AC, TLI, TTI, DT,
-                        ORE, BFI, BPI, PSI, DL, RPOT);
+                        ORE, BFI, BPI, PSI, DL, RPOT, Opts.CleanupAssumptions);
     IC.MaxArraySizeForCombine = MaxArraySize;
     bool MadeChangeInThisIteration = IC.prepareWorklist(F);
     MadeChangeInThisIteration |= IC.run();
@@ -5573,7 +5573,7 @@ PreservedAnalyses InstCombinePass::run(Function &F,
                                        FunctionAnalysisManager &AM) {
   auto &LRT = AM.getResult<LastRunTrackingAnalysis>(F);
   // No changes since last InstCombine pass, exit early.
-  if (LRT.shouldSkip(&ID))
+  if (LRT.shouldSkip(&ID) && !Options.CleanupAssumptions)
     return PreservedAnalyses::all();
 
   auto &AC = AM.getResult<AssumptionAnalysis>(F);