[SCCP] Propagate integer range info for parameters in IPSCCP.

Summary:
This updates the SCCP solver to use of the ValueElement lattice for 
parameters, which provides integer range information. The range
information is used to remove unneeded icmp instructions.

For the following function, f() can be optimized to `ret i32 2` with
this change

  source_filename = "sccp.c"
  target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
  target triple = "x86_64-unknown-linux-gnu"
  
  ; Function Attrs: norecurse nounwind readnone uwtable
  define i32 @main() local_unnamed_addr #0 {
  entry:
    %call = tail call fastcc i32 @f(i32 1)
    %call1 = tail call fastcc i32 @f(i32 47)
    %add3 = add nsw i32 %call, %call1
    ret i32 %add3
  }
  
  ; Function Attrs: noinline norecurse nounwind readnone uwtable
  define internal fastcc i32 @f(i32 %x) unnamed_addr #1 {
  entry:
    %c1 = icmp sle i32 %x, 100
  
    %cmp = icmp sgt i32 %x, 300
    %. = select i1 %cmp, i32 1, i32 2
    ret i32 %.
  }
  
  attributes #1 = { noinline }



Reviewers: davide, sanjoy, efriedma, dberlin

Reviewed By: davide, dberlin

Subscribers: mcrosier, gberry, mssimpso, dberlin, llvm-commits

Differential Revision: https://reviews.llvm.org/D36656

llvm-svn: 315288

llvm/lib/Transforms/Scalar/SCCP.cpp

@@ -27,6 +27,7 @@
 #include "llvm/Analysis/ConstantFolding.h"
 #include "llvm/Analysis/GlobalsModRef.h"
 #include "llvm/Analysis/TargetLibraryInfo.h"
+#include "llvm/Analysis/ValueLattice.h"
 #include "llvm/IR/CallSite.h"
 #include "llvm/IR/Constants.h"
 #include "llvm/IR/DataLayout.h"
@@ -52,6 +53,8 @@ STATISTIC(NumDeadBlocks , "Number of basic blocks unreachable");
 STATISTIC(IPNumInstRemoved, "Number of instructions removed by IPSCCP");
 STATISTIC(IPNumArgsElimed ,"Number of arguments constant propagated by IPSCCP");
 STATISTIC(IPNumGlobalConst, "Number of globals found to be constant by IPSCCP");
+STATISTIC(IPNumRangeInfoUsed, "Number of times constant range info was used by"
+                              "IPSCCP");
 
 namespace {
 /// LatticeVal class - This class represents the different lattice values that
@@ -153,6 +156,14 @@ class LatticeVal {
     Val.setInt(forcedconstant);
     Val.setPointer(V);
   }
+
+  ValueLatticeElement toValueLattice() const {
+    if (isOverdefined())
+      return ValueLatticeElement::getOverdefined();
+    if (isConstant())
+      return ValueLatticeElement::get(getConstant());
+    return ValueLatticeElement();
+  }
 };
 } // end anonymous namespace.
 
@@ -169,6 +180,8 @@ class SCCPSolver : public InstVisitor<SCCPSolver> {
   const TargetLibraryInfo *TLI;
   SmallPtrSet<BasicBlock*, 8> BBExecutable; // The BBs that are executable.
   DenseMap<Value*, LatticeVal> ValueState;  // The state each value is in.
+  // The state each parameter is in.
+  DenseMap<Value *, ValueLatticeElement> ParamState;
 
   /// StructValueState - This maintains ValueState for values that have
   /// StructType, for example for formal arguments, calls, insertelement, etc.
@@ -290,10 +303,15 @@ class SCCPSolver : public InstVisitor<SCCPSolver> {
     return StructValues;
   }
 
-  LatticeVal getLatticeValueFor(Value *V) const {
-    DenseMap<Value*, LatticeVal>::const_iterator I = ValueState.find(V);
-    assert(I != ValueState.end() && "V is not in valuemap!");
-    return I->second;
+  ValueLatticeElement getLatticeValueFor(Value *V) {
+    if (ParamState.count(V) == 0) {
+      DenseMap<Value *, LatticeVal>::const_iterator I = ValueState.find(V);
+      assert(I != ValueState.end() &&
+             "V not found in ValueState nor Paramstate map!");
+      ParamState[V] = I->second.toValueLattice();
+    }
+
+    return ParamState[V];
   }
 
   /// getTrackedRetVals - Get the inferred return value map.
@@ -426,6 +444,15 @@ class SCCPSolver : public InstVisitor<SCCPSolver> {
     return LV;
   }
 
+  ValueLatticeElement &getParamState(Value *V) {
+    assert(!V->getType()->isStructTy() && "Should use getStructValueState");
+
+    if (ParamState.count(V) == 0)
+      ParamState[V] = getValueState(V).toValueLattice();
+
+    return ParamState[V];
+  }
+
   /// getStructValueState - Return the LatticeVal object that corresponds to the
   /// value/field pair.  This function handles the case when the value hasn't
   /// been seen yet by properly seeding constants etc.
@@ -1162,6 +1189,9 @@ void SCCPSolver::visitCallSite(CallSite CS) {
           mergeInValue(getStructValueState(&*AI, i), &*AI, CallArg);
         }
       } else {
+        // Most other parts of the Solver still only use the simpler value
+        // lattice, so we propagate changes for parameters to both lattices.
+        getParamState(&*AI).mergeIn(getValueState(*CAI).toValueLattice(), DL);
         mergeInValue(&*AI, getValueState(*CAI));
       }
     }
@@ -1557,6 +1587,44 @@ bool SCCPSolver::ResolvedUndefsIn(Function &F) {
   return false;
 }
 
+static bool tryToReplaceWithConstantRange(SCCPSolver &Solver, Value *V) {
+  bool Changed = false;
+  if (!V->getType()->isIntegerTy())
+    return false;
+
+  const ValueLatticeElement &IV = Solver.getLatticeValueFor(V);
+  if (IV.isOverdefined())
+    return false;
+
+  // Currently we only use range information for integer values.
+  if (!(V->getType()->isIntegerTy() && IV.isConstantRange()))
+    return false;
+
+  for (auto &Use : V->uses()) {
+    auto *Icmp = dyn_cast<ICmpInst>(Use.getUser());
+    if (!Icmp)
+      continue;
+
+    auto A = Solver.getLatticeValueFor(Icmp->getOperand(0));
+    auto B = Solver.getLatticeValueFor(Icmp->getOperand(1));
+    Constant *C = nullptr;
+    if (A.satisfiesPredicate(Icmp->getPredicate(), B))
+      C = ConstantInt::getTrue(Icmp->getType());
+    else if (A.satisfiesPredicate(Icmp->getInversePredicate(), B))
+      C = ConstantInt::getFalse(Icmp->getType());
+
+    if (C) {
+      Icmp->replaceAllUsesWith(C);
+      DEBUG(dbgs() << "Replacing " << *Icmp << " with " << *C
+                   << ", because of range information " << A << " " << B
+                   << "\n");
+      Icmp->eraseFromParent();
+      Changed = true;
+    }
+  }
+  return Changed;
+}
+
 static bool tryToReplaceWithConstant(SCCPSolver &Solver, Value *V) {
   Constant *Const = nullptr;
   if (V->getType()->isStructTy()) {
@@ -1573,10 +1641,19 @@ static bool tryToReplaceWithConstant(SCCPSolver &Solver, Value *V) {
     }
     Const = ConstantStruct::get(ST, ConstVals);
   } else {
-    LatticeVal IV = Solver.getLatticeValueFor(V);
+    const ValueLatticeElement &IV = Solver.getLatticeValueFor(V);
     if (IV.isOverdefined())
       return false;
-    Const = IV.isConstant() ? IV.getConstant() : UndefValue::get(V->getType());
+
+    if (IV.isConstantRange()) {
+      if (IV.getConstantRange().isSingleElement())
+        Const =
+            ConstantInt::get(V->getType(), IV.asConstantInteger().getValue());
+      else
+        return false;
+    } else
+      Const =
+          IV.isConstant() ? IV.getConstant() : UndefValue::get(V->getType());
   }
   assert(Const && "Constant is nullptr here!");
   DEBUG(dbgs() << "  Constant: " << *Const << " = " << *V << '\n');
@@ -1816,12 +1893,17 @@ static bool runIPSCCP(Module &M, const DataLayout &DL,
     if (F.isDeclaration())
       continue;
 
-    if (Solver.isBlockExecutable(&F.front()))
+    if (Solver.isBlockExecutable(&F.front())) {
       for (Function::arg_iterator AI = F.arg_begin(), E = F.arg_end(); AI != E;
-           ++AI)
+           ++AI) {
         if (!AI->use_empty() && tryToReplaceWithConstant(Solver, &*AI))
           ++IPNumArgsElimed;
 
+        if (!AI->use_empty() && tryToReplaceWithConstantRange(Solver, &*AI))
+          ++IPNumRangeInfoUsed;
+      }
+    }
+
     for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) {
       if (!Solver.isBlockExecutable(&*BB)) {
         DEBUG(dbgs() << "  BasicBlock Dead:" << *BB);

llvm/test/Transforms/SCCP/ip-constan-ranges.ll

@@ -0,0 +1,117 @@
+; RUN: opt < %s -ipsccp -S | FileCheck %s
+
+; Constant range for %a is [1, 48) and for %b is [301, 1000)
+; CHECK-LABEL: f1
+; CHECK-NOT: icmp
+; CHECK: %a.1 = select i1 false, i32 1, i32 2
+; CHECK: %b.1 = select i1 true, i32 1, i32 2
+; CHECK: %a.2 = select i1 false, i32 1, i32 2
+; CHECK: %b.2 = select i1 true, i32 1, i32 2
+define internal i32 @f1(i32 %a, i32 %b) {
+entry:
+  %cmp.a = icmp sgt i32 %a, 300
+  %cmp.b = icmp sgt i32 %b, 300
+  %cmp.a2 = icmp ugt i32 %a, 300
+  %cmp.b2 = icmp ugt i32 %b, 300
+
+  %a.1 = select i1 %cmp.a, i32 1, i32 2
+  %b.1 = select i1 %cmp.b, i32 1, i32 2
+  %a.2 = select i1 %cmp.a2, i32 1, i32 2
+  %b.2 = select i1 %cmp.b2, i32 1, i32 2
+  %res1 = add i32 %a.1, %b.1
+  %res2 = add i32 %a.2, %b.2
+  %res3 = add i32 %res1, %res2
+  ret i32 %res3
+}
+
+; Constant range for %x is [47, 302)
+; CHECK-LABEL: f2
+; CHECK: %cmp = icmp sgt i32 %x, 300
+; CHECK: %res1 = select i1 %cmp, i32 1, i32 2
+; CHECK-NEXT: %res2 = select i1 true, i32 3, i32 4
+; CHECK-NEXT: %res3 = select i1 true, i32 5, i32 6
+; CHECK-NEXT: %res4 = select i1 %cmp4, i32 3, i32 4
+; CHECK-NEXT: %res5 = select i1 true, i32 5, i32 6
+define internal i32 @f2(i32 %x) {
+entry:
+  %cmp = icmp sgt i32 %x, 300
+  %cmp2 = icmp ne i32 %x, 10
+  %cmp3 = icmp sge i32 %x, 47
+  %cmp4 = icmp ugt i32 %x, 300
+  %cmp5 = icmp uge i32 %x, 47
+  %res1 = select i1 %cmp, i32 1, i32 2
+  %res2 = select i1 %cmp2, i32 3, i32 4
+  %res3 = select i1 %cmp3, i32 5, i32 6
+  %res4 = select i1 %cmp4, i32 3, i32 4
+  %res5 = select i1 %cmp5, i32 5, i32 6
+
+  %res6 = add i32 %res1, %res2
+  %res7 = add i32 %res3, %res4
+  %res = add i32 %res6, %res5
+  ret i32 %res
+}
+
+define i32 @caller1() {
+entry:
+  %call1 = tail call i32 @f1(i32 1, i32 301)
+  %call2 = tail call i32 @f1(i32 47, i32 999)
+  %call3 = tail call i32 @f2(i32 47)
+  %call4 = tail call i32 @f2(i32 301)
+  %res = add nsw i32 %call1, %call2
+  %res.1 = add nsw i32 %res, %call3
+  %res.2 = add nsw i32 %res.1, %call4
+  ret i32 %res.2
+}
+
+; x is overdefined, because constant ranges are only used for parameter
+; values.
+; CHECK-LABEL: f3
+; CHECK: %cmp = icmp sgt i32 %x, 300
+; CHECK: %res = select i1 %cmp, i32 1, i32 2
+; CHECK: ret i32 %res
+define internal i32 @f3(i32 %x) {
+entry:
+  %cmp = icmp sgt i32 %x, 300
+  %res = select i1 %cmp, i32 1, i32 2
+  ret i32 %res
+}
+
+; The phi node could be converted in a ConstantRange.
+define i32 @caller2(i1 %cmp) {
+entry:
+  br i1 %cmp, label %if.true, label %end
+
+if.true:
+  br label %end
+
+end:
+  %res = phi i32 [ 0, %entry], [ 1, %if.true ]
+  %call1 = tail call i32 @f3(i32 %res)
+  ret i32 %call1
+}
+
+; CHECK-LABEL: f4
+; CHECK: %cmp = icmp sgt i32 %x, 300
+; CHECK: %res = select i1 %cmp, i32 1, i32 2
+; CHECK: ret i32 %res
+define internal i32 @f4(i32 %x) {
+entry:
+  %cmp = icmp sgt i32 %x, 300
+  %res = select i1 %cmp, i32 1, i32 2
+  ret i32 %res
+}
+
+; ICmp could introduce bounds on ConstantRanges.
+define i32 @caller3(i32 %x) {
+entry:
+  %cmp = icmp sgt i32 %x, 300
+  br i1 %cmp, label %if.true, label %end
+
+if.true:
+  %x.1 = tail call i32 @f4(i32 %x)
+  br label %end
+
+end:
+  %res = phi i32 [ 0, %entry], [ %x.1, %if.true ]
+  ret i32 %res
+}