[LVI] Thread binop over select with constant arms

Author: dtcxzyw

llvm/lib/Analysis/LazyValueInfo.cpp

@@ -924,18 +924,74 @@ LazyValueInfoImpl::solveBlockValueBinaryOpImpl(
     Instruction *I, BasicBlock *BB,
     std::function<ConstantRange(const ConstantRange &, const ConstantRange &)>
         OpFn) {
+  Value *LHS = I->getOperand(0);
+  Value *RHS = I->getOperand(1);
+
+  auto GetValueFromCondition =
+      [&](Value *V, Value *Cond,
+          bool CondIsTrue) -> std::optional<ConstantRange> {
+    std::optional<ValueLatticeElement> OptVal = getBlockValue(V, BB, I);
+    if (!OptVal)
+      return std::nullopt;
+    return OptVal->asConstantRange(V->getType());
+  };
+
+  auto ThreadBinOpOverSelect =
+      [&](Value *X, const ConstantRange &CRX, SelectInst *Y,
+          bool XIsLHS) -> std::optional<ValueLatticeElement> {
+    Value *Cond = Y->getCondition();
+    // Only handle selects with constant values.
+    Constant *TrueC = dyn_cast<Constant>(Y->getTrueValue());
+    if (!TrueC)
+      return std::nullopt;
+    Constant *FalseC = dyn_cast<Constant>(Y->getFalseValue());
+    if (!FalseC)
+      return std::nullopt;
+    if (!isGuaranteedNotToBeUndef(Cond, AC))
+      return std::nullopt;
+
+    ConstantRange TrueX =
+        CRX.intersectWith(getValueFromCondition(X, Cond, /*CondIsTrue=*/true,
+                                                /*UseBlockValue=*/false)
+                              ->asConstantRange(X->getType()));
+    ConstantRange FalseX =
+        CRX.intersectWith(getValueFromCondition(X, Cond, /*CondIsTrue=*/false,
+                                                /*UseBlockValue=*/false)
+                              ->asConstantRange(X->getType()));
+    ConstantRange TrueY = TrueC->toConstantRange();
+    ConstantRange FalseY = FalseC->toConstantRange();
+
+    if (XIsLHS)
+      return ValueLatticeElement::getRange(
+          OpFn(TrueX, TrueY).unionWith(OpFn(FalseX, FalseY)));
+    return ValueLatticeElement::getRange(
+        OpFn(TrueY, TrueX).unionWith(OpFn(FalseY, FalseX)));
+  };
+
   // Figure out the ranges of the operands.  If that fails, use a
   // conservative range, but apply the transfer rule anyways.  This
   // lets us pick up facts from expressions like "and i32 (call i32
   // @foo()), 32"
-  std::optional<ConstantRange> LHSRes = getRangeFor(I->getOperand(0), I, BB);
+  std::optional<ConstantRange> LHSRes = getRangeFor(LHS, I, BB);
   if (!LHSRes)
     return std::nullopt;
 
-  std::optional<ConstantRange> RHSRes = getRangeFor(I->getOperand(1), I, BB);
+  // Try to thread binop over rhs select
+  if (auto *SI = dyn_cast<SelectInst>(RHS)) {
+    if (auto Res = ThreadBinOpOverSelect(LHS, *LHSRes, SI, /*XIsLHS=*/true))
+      return *Res;
+  }
+
+  std::optional<ConstantRange> RHSRes = getRangeFor(RHS, I, BB);
   if (!RHSRes)
     return std::nullopt;
 
+  // Try to thread binop over lhs select
+  if (auto *SI = dyn_cast<SelectInst>(LHS)) {
+    if (auto Res = ThreadBinOpOverSelect(RHS, *RHSRes, SI, /*XIsLHS=*/false))
+      return *Res;
+  }
+
   const ConstantRange &LHSRange = *LHSRes;
   const ConstantRange &RHSRange = *RHSRes;
   return ValueLatticeElement::getRange(OpFn(LHSRange, RHSRange));

llvm/test/Transforms/CorrelatedValuePropagation/cond-at-use.ll

@@ -638,8 +638,7 @@ define i1 @test_icmp_mod(i64 noundef %x) {
 ; CHECK-NEXT:    [[CMP:%.*]] = icmp slt i64 [[REM]], 0
 ; CHECK-NEXT:    [[COND:%.*]] = select i1 [[CMP]], i64 86400, i64 0
 ; CHECK-NEXT:    [[ADD:%.*]] = add nsw i64 [[COND]], [[REM]]
-; CHECK-NEXT:    [[CMP1:%.*]] = icmp ugt i64 [[ADD]], 86399
-; CHECK-NEXT:    ret i1 [[CMP1]]
+; CHECK-NEXT:    ret i1 false
 ;
 entry:
   %rem = srem i64 %x, 86400