[llvm] [llvm] Use LazyValueInfo to improve llvm.objectsize computation (PR #114673)

[via llvm-commits]

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@@ -856,6 +910,48 @@ OffsetSpan ObjectSizeOffsetVisitor::visitGlobalVariable(GlobalVariable &GV) {
   return OffsetSpan(Zero, align(Size, GV.getAlign()));
 }
 
+OffsetSpan ObjectSizeOffsetVisitor::visitGetElementPtr(GetElementPtrInst &GEP) {
+  OffsetSpan PtrData = computeImpl(GEP.getPointerOperand());
+  if (!PtrData.bothKnown())
+    return ObjectSizeOffsetVisitor::unknown();
+
+  if (Options.EvalMode == ObjectSizeOpts::Mode::Min ||
+      Options.EvalMode == ObjectSizeOpts::Mode::Max) {
+    unsigned BitWidth = PtrData.After.getBitWidth();
+    APInt ConstantOffset = Zero;
+    SmallMapVector<Value *, APInt, 4> VariableOffsets;
+    if (!GEP.collectOffset(DL, BitWidth, VariableOffsets, ConstantOffset))
+      return ObjectSizeOffsetVisitor::unknown();
+
+    ConstantRange AccumulatedRange = ConstantOffset;
+    for (auto const &VO : VariableOffsets) {
+      ConstantRange CR = computeConstantRange(
+          VO.first, /*ForSigned*/ true, /*UseInstrInfo*/ true, /*AC=*/nullptr,
+          /*CtxtI=*/&GEP, /*DT=*/Options.DT);
+      if (CR.isFullSet())
+        return ObjectSizeOffsetVisitor::unknown();
+
+      AccumulatedRange = AccumulatedRange.add(CR.multiply(VO.second));
+    }
+
+    APInt Bound;
+    if (Options.EvalMode == ObjectSizeOpts::Mode::Min) {
+      Bound = AccumulatedRange.getSignedMax();
+      // Upper bound actually unknown.
+      if (Bound.isMaxSignedValue())
+        return ObjectSizeOffsetVisitor::unknown();
+    } else {
+      Bound = AccumulatedRange.getSignedMin();
+      // Lower bound actually unknown.
+      if (Bound.isMinSignedValue())
+        return ObjectSizeOffsetVisitor::unknown();
+    }
+
+    return {PtrData.Before + Bound, PtrData.After - Bound};
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serge-sans-paille wrote:

it turns out `stripAndAccumulateConstantOffset` accepts an optional argument that makes it possible to plug our analysis, so I used it and as a side effect it delegates the answer to your question to this function ;-)

https://github.com/llvm/llvm-project/pull/114673