[CVP] Remove unnecessary checks for empty GNWR; NFC

The guaranteed no-wrap region is never empty, it always contains at
least zero, so these optimizations don't ever apply.

To make this more obviously true, replace the conversative return
in makeGNWR with an assertion.

llvm-svn: 361698

Author: nikic

llvm/lib/IR/ConstantRange.cpp

@@ -238,8 +238,7 @@ ConstantRange::makeGuaranteedNoWrapRegion(Instruction::BinaryOps BinOp,
 
   switch (BinOp) {
   default:
-    // Conservative answer: empty set
-    return getEmpty(BitWidth);
+    llvm_unreachable("Unsupported binary op");
 
   case Instruction::Add: {
     if (Unsigned)

llvm/lib/Transforms/Scalar/CorrelatedValuePropagation.cpp

@@ -400,15 +400,12 @@ static bool processSwitch(SwitchInst *SI, LazyValueInfo *LVI,
 
 // See if we can prove that the given overflow intrinsic will not overflow.
 static bool willNotOverflow(WithOverflowInst *WO, LazyValueInfo *LVI) {
-  Value *RHS = WO->getRHS();
-  ConstantRange RRange = LVI->getConstantRange(RHS, WO->getParent(), WO);
+  ConstantRange LRange = LVI->getConstantRange(
+      WO->getLHS(), WO->getParent(), WO);
+  ConstantRange RRange = LVI->getConstantRange(
+      WO->getRHS(), WO->getParent(), WO);
   ConstantRange NWRegion = ConstantRange::makeGuaranteedNoWrapRegion(
       WO->getBinaryOp(), RRange, WO->getNoWrapKind());
-  // As an optimization, do not compute LRange if we do not need it.
-  if (NWRegion.isEmptySet())
-    return false;
-  Value *LHS = WO->getLHS();
-  ConstantRange LRange = LVI->getConstantRange(LHS, WO->getParent(), WO);
   return NWRegion.contains(LRange);
 }
 
@@ -626,36 +623,23 @@ static bool processBinOp(BinaryOperator *BinOp, LazyValueInfo *LVI) {
   Value *LHS = BinOp->getOperand(0);
   Value *RHS = BinOp->getOperand(1);
 
+  ConstantRange LRange = LVI->getConstantRange(LHS, BB, BinOp);
   ConstantRange RRange = LVI->getConstantRange(RHS, BB, BinOp);
 
-  // Initialize LRange only if we need it. If we know that guaranteed no wrap
-  // range for the given RHS range is empty don't spend time calculating the
-  // range for the LHS.
-  Optional<ConstantRange> LRange;
-  auto LazyLRange = [&] () {
-      if (!LRange)
-        LRange = LVI->getConstantRange(LHS, BB, BinOp);
-      return LRange.getValue();
-  };
-
   bool Changed = false;
   if (!NUW) {
     ConstantRange NUWRange = ConstantRange::makeGuaranteedNoWrapRegion(
         BinOp->getOpcode(), RRange, OBO::NoUnsignedWrap);
-    if (!NUWRange.isEmptySet()) {
-      bool NewNUW = NUWRange.contains(LazyLRange());
-      BinOp->setHasNoUnsignedWrap(NewNUW);
-      Changed |= NewNUW;
-    }
+    bool NewNUW = NUWRange.contains(LRange);
+    BinOp->setHasNoUnsignedWrap(NewNUW);
+    Changed |= NewNUW;
   }
   if (!NSW) {
     ConstantRange NSWRange = ConstantRange::makeGuaranteedNoWrapRegion(
         BinOp->getOpcode(), RRange, OBO::NoSignedWrap);
-    if (!NSWRange.isEmptySet()) {
-      bool NewNSW = NSWRange.contains(LazyLRange());
-      BinOp->setHasNoSignedWrap(NewNSW);
-      Changed |= NewNSW;
-    }
+    bool NewNSW = NSWRange.contains(LRange);
+    BinOp->setHasNoSignedWrap(NewNSW);
+    Changed |= NewNSW;
   }
 
   return Changed;