[llvm] [InstCombine] Fold icmp(constants[x]) when the range of x is given (PR #67093)

[via llvm-commits]

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@@ -187,43 +167,58 @@ Instruction *InstCombinerImpl::foldCmpLoadFromIndexedGlobal(
   // the array, this will fully represent all the comparison results.
   uint64_t MagicBitvector = 0;
 
+  Value *Idx = nullptr;
+
   // Scan the array and see if one of our patterns matches.
-  Constant *CompareRHS = cast<Constant>(ICI.getOperand(1));
-  for (unsigned i = 0, e = ArrayElementCount; i != e; ++i) {
-    Constant *Elt = Init->getAggregateElement(i);
-    if (!Elt) return nullptr;
-
-    // If this is indexing an array of structures, get the structure element.
-    if (!LaterIndices.empty()) {
-      Elt = ConstantFoldExtractValueInstruction(Elt, LaterIndices);
-      if (!Elt)
-        return nullptr;
-    }
+  Constant *ComparedRHS = cast<Constant>(ICI.getOperand(1));
+  // The longest step we can reach once.
+  APInt OffsetStep = VariableOffsets.front().second;
+
+  // BeginOffset is the offset from constant pointer where we begin scanning the
+  // constant. Make BeginOffset the smallest offset greater than 0
+  APInt BeginOffset = ConstantOffset.srem(OffsetStep);
+  if (BeginOffset.slt(0))
+    BeginOffset += OffsetStep;
+
+  uint64_t ElementCountToTraverse = (DataSize - BeginOffset).udiv(OffsetStep).getZExtValue() + 1;
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XChy wrote:

I missed "+1" here, actually `BeginOffset` indeed includes one more element. Fix it now.

https://github.com/llvm/llvm-project/pull/67093