[JumpThreading] Teach jump threading how to analyze (and (cmp A, C1), (cmp A, C2...

Currently JumpThreading can use LazyValueInfo to analyze an 'and' or 'or' of compare if the compare is fed by a livein of a basic block. This can be used to to prove the condition can't be met for some predecessor and the jump from that predecessor can be moved to the false path of the condition.

But if the compare is something that InstCombine turns into an add and a single compare, it can't be analyzed because the livein is now an input to the add and not the compare.

This patch adds a new method to LVI to get a ConstantRange on an edge. Then we teach jump threading to detect the add livein feeding a compare and to get the ConstantRange and propagate it.

Differential Revision: https://reviews.llvm.org/D33262

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@306085 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/include/llvm/Analysis/LazyValueInfo.h b/include/llvm/Analysis/LazyValueInfo.h
index 7b178fc7bcc21db47978c8f63ccc58374d192037..787c88cc6ec1a6040a1e5b811a3a1c7e05bc93d6 100644 (file)
--- a/include/llvm/Analysis/LazyValueInfo.h
+++ b/include/llvm/Analysis/LazyValueInfo.h
@@ -93,6 +93,13 @@ public:
   Constant *getConstantOnEdge(Value *V, BasicBlock *FromBB, BasicBlock *ToBB,
                               Instruction *CxtI = nullptr);
 
+  /// Return the ConstantRage constraint that is known to hold for the
+  /// specified value on the specified edge. This may be only be called
+  /// on integer-typed Values.
+  ConstantRange getConstantRangeOnEdge(Value *V, BasicBlock *FromBB,
+                                       BasicBlock *ToBB,
+                                       Instruction *CxtI = nullptr);
+
   /// Inform the analysis cache that we have threaded an edge from
   /// PredBB to OldSucc to be from PredBB to NewSucc instead.
   void threadEdge(BasicBlock *PredBB, BasicBlock *OldSucc, BasicBlock *NewSucc);

diff --git a/lib/Analysis/LazyValueInfo.cpp b/lib/Analysis/LazyValueInfo.cpp
index a5d6e670f72f3bc956ce5fda2a622cc407e3cdcd..102081e721ac6b053b5d059c04afd08227c105aa 100644 (file)
--- a/lib/Analysis/LazyValueInfo.cpp
+++ b/lib/Analysis/LazyValueInfo.cpp
@@ -1660,6 +1660,26 @@ Constant *LazyValueInfo::getConstantOnEdge(Value *V, BasicBlock *FromBB,
   return nullptr;
 }
 
+ConstantRange LazyValueInfo::getConstantRangeOnEdge(Value *V,
+                                                    BasicBlock *FromBB,
+                                                    BasicBlock *ToBB,
+                                                    Instruction *CxtI) {
+  unsigned Width = V->getType()->getIntegerBitWidth();
+  const DataLayout &DL = FromBB->getModule()->getDataLayout();
+  LVILatticeVal Result =
+      getImpl(PImpl, AC, &DL, DT).getValueOnEdge(V, FromBB, ToBB, CxtI);
+
+  if (Result.isUndefined())
+    return ConstantRange(Width, /*isFullSet=*/false);
+  if (Result.isConstantRange())
+    return Result.getConstantRange();
+  // We represent ConstantInt constants as constant ranges but other kinds
+  // of integer constants, i.e. ConstantExpr will be tagged as constants
+  assert(!(Result.isConstant() && isa<ConstantInt>(Result.getConstant())) &&
+         "ConstantInt value must be represented as constantrange");
+  return ConstantRange(Width, /*isFullSet=*/true);
+}
+
 static LazyValueInfo::Tristate getPredicateResult(unsigned Pred, Constant *C,
                                                   const LVILatticeVal &Val,
                                                   const DataLayout &DL,

diff --git a/lib/Transforms/Scalar/JumpThreading.cpp b/lib/Transforms/Scalar/JumpThreading.cpp
index 011a81e1654f3cc0cf8ff1d1a8d30bd372197c12..05293eb0079fc84dc90b399ddf46bd418126f46a 100644 (file)
--- a/lib/Transforms/Scalar/JumpThreading.cpp
+++ b/lib/Transforms/Scalar/JumpThreading.cpp
@@ -25,6 +25,7 @@
 #include "llvm/Analysis/Loads.h"
 #include "llvm/Analysis/LoopInfo.h"
 #include "llvm/Analysis/ValueTracking.h"
+#include "llvm/IR/ConstantRange.h"
 #include "llvm/IR/DataLayout.h"
 #include "llvm/IR/IntrinsicInst.h"
 #include "llvm/IR/LLVMContext.h"
@@ -635,6 +636,46 @@ bool JumpThreadingPass::ComputeValueKnownInPredecessors(
         return !Result.empty();
       }
 
+      // InstCombine can fold some forms of constant range checks into
+      // (icmp (add (x, C1)), C2). See if we have we have such a thing with
+      // x as a live-in.
+      {
+        using namespace PatternMatch;
+        Value *AddLHS;
+        ConstantInt *AddConst;
+        if (isa<ConstantInt>(CmpConst) &&
+            match(CmpLHS, m_Add(m_Value(AddLHS), m_ConstantInt(AddConst)))) {
+          if (!isa<Instruction>(AddLHS) ||
+              cast<Instruction>(AddLHS)->getParent() != BB) {
+            for (BasicBlock *P : predecessors(BB)) {
+              // If the value is known by LazyValueInfo to be a ConstantRange in
+              // a predecessor, use that information to try to thread this
+              // block.
+              ConstantRange CR = LVI->getConstantRangeOnEdge(
+                  AddLHS, P, BB, CxtI ? CxtI : cast<Instruction>(CmpLHS));
+              // Propagate the range through the addition.
+              CR = CR.add(AddConst->getValue());
+
+              // Get the range where the compare returns true.
+              ConstantRange CmpRange = ConstantRange::makeExactICmpRegion(
+                  Pred, cast<ConstantInt>(CmpConst)->getValue());
+
+              Constant *ResC;
+              if (CmpRange.contains(CR))
+                ResC = ConstantInt::getTrue(CmpType);
+              else if (CmpRange.inverse().contains(CR))
+                ResC = ConstantInt::getFalse(CmpType);
+              else
+                continue;
+
+              Result.push_back(std::make_pair(ResC, P));
+            }
+
+            return !Result.empty();
+          }
+        }
+      }
+
       // Try to find a constant value for the LHS of a comparison,
       // and evaluate it statically if we can.
       PredValueInfoTy LHSVals;