[SCEV] See through op.with.overflow intrinsics

Summary:
This change teaches SCEV to see reduce `(extractvalue
0 (op.with.overflow X Y))` into `op X Y` (with a no-wrap tag if
possible).

Reviewers: atrick, regehr

Subscribers: mcrosier, mzolotukhin, llvm-commits

Differential Revision: http://reviews.llvm.org/D18684

llvm-svn: 265912

1 files changed, 49 insertions, 5 deletions

diff --git a/llvm/lib/Analysis/ScalarEvolution.cpp b/llvm/lib/Analysis/ScalarEvolution.cpp
index 654a766b416..6366e3621ae 100644
--- a/llvm/lib/Analysis/ScalarEvolution.cpp
+++ b/llvm/lib/Analysis/ScalarEvolution.cpp
@@ -3831,7 +3831,7 @@ struct BinaryOp {
 
 
 /// Try to map \p V into a BinaryOp, and return \c None on failure.
-static Optional<BinaryOp> MatchBinaryOp(Value *V) {
+static Optional<BinaryOp> MatchBinaryOp(Value *V, DominatorTree &DT) {
   auto *Op = dyn_cast<Operator>(V);
   if (!Op)
     return None;
@@ -3877,6 +3877,50 @@ static Optional<BinaryOp> MatchBinaryOp(Value *V) {
     }
     return BinaryOp(Op);
 
+  case Instruction::ExtractValue: {
+    auto *EVI = cast<ExtractValueInst>(Op);
+    if (EVI->getNumIndices() != 1 || EVI->getIndices()[0] != 0)
+      break;
+
+    auto *CI = dyn_cast<CallInst>(EVI->getAggregateOperand());
+    if (!CI)
+      break;
+
+    if (auto *F = CI->getCalledFunction())
+      switch (F->getIntrinsicID()) {
+      case Intrinsic::sadd_with_overflow:
+      case Intrinsic::uadd_with_overflow: {
+        if (!isOverflowIntrinsicNoWrap(cast<IntrinsicInst>(CI), DT))
+          return BinaryOp(Instruction::Add, CI->getArgOperand(0),
+                          CI->getArgOperand(1));
+
+        // Now that we know that all uses of the arithmetic-result component of
+        // CI are guarded by the overflow check, we can go ahead and pretend
+        // that the arithmetic is non-overflowing.
+        if (F->getIntrinsicID() == Intrinsic::sadd_with_overflow)
+          return BinaryOp(Instruction::Add, CI->getArgOperand(0),
+                          CI->getArgOperand(1), /* IsNSW = */ true,
+                          /* IsNUW = */ false);
+        else
+          return BinaryOp(Instruction::Add, CI->getArgOperand(0),
+                          CI->getArgOperand(1), /* IsNSW = */ false,
+                          /* IsNUW*/ true);
+      }
+
+      case Intrinsic::ssub_with_overflow:
+      case Intrinsic::usub_with_overflow:
+        return BinaryOp(Instruction::Sub, CI->getArgOperand(0),
+                        CI->getArgOperand(1));
+
+      case Intrinsic::smul_with_overflow:
+      case Intrinsic::umul_with_overflow:
+        return BinaryOp(Instruction::Mul, CI->getArgOperand(0),
+                        CI->getArgOperand(1));
+      default:
+        break;
+      }
+  }
+
   default:
     break;
   }
@@ -3953,7 +3997,7 @@ const SCEV *ScalarEvolution::createAddRecFromPHI(PHINode *PN) {
 
           // If the increment doesn't overflow, then neither the addrec nor
           // the post-increment will overflow.
-          if (auto BO = MatchBinaryOp(BEValueV)) {
+          if (auto BO = MatchBinaryOp(BEValueV, DT)) {
             if (BO->Opcode == Instruction::Add && BO->LHS == PN) {
               if (BO->IsNUW)
                 Flags = setFlags(Flags, SCEV::FlagNUW);
@@ -4833,7 +4877,7 @@ const SCEV *ScalarEvolution::createSCEV(Value *V) {
     return getUnknown(V);
 
   Operator *U = cast<Operator>(V);
-  if (auto BO = MatchBinaryOp(U)) {
+  if (auto BO = MatchBinaryOp(U, DT)) {
     switch (BO->Opcode) {
     case Instruction::Add: {
       // The simple thing to do would be to just call getSCEV on both operands
@@ -4874,7 +4918,7 @@ const SCEV *ScalarEvolution::createSCEV(Value *V) {
         else
           AddOps.push_back(getSCEV(BO->RHS));
 
-        auto NewBO = MatchBinaryOp(BO->LHS);
+        auto NewBO = MatchBinaryOp(BO->LHS, DT);
         if (!NewBO || (NewBO->Opcode != Instruction::Add &&
                        NewBO->Opcode != Instruction::Sub)) {
           AddOps.push_back(getSCEV(BO->LHS));
@@ -4904,7 +4948,7 @@ const SCEV *ScalarEvolution::createSCEV(Value *V) {
         }
 
         MulOps.push_back(getSCEV(BO->RHS));
-        auto NewBO = MatchBinaryOp(BO->LHS);
+        auto NewBO = MatchBinaryOp(BO->LHS, DT);
         if (!NewBO || NewBO->Opcode != Instruction::Mul) {
           MulOps.push_back(getSCEV(BO->LHS));
           break;