[llvm] Add ConstantRangeList::subtract(ConstantRange) (PR #97093)

[Jan Voung via llvm-commits]

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@@ -81,6 +81,65 @@ void ConstantRangeList::insert(const ConstantRange &NewRange) {
   }
 }
 
+void ConstantRangeList::subtract(const ConstantRange &SubRange) {
+  if (SubRange.isEmptySet())
+    return;
+  assert(!SubRange.isFullSet() && "Do not support full set");
+  assert(SubRange.getLower().slt(SubRange.getUpper()));
+  assert(getBitWidth() == SubRange.getBitWidth());
+  // Handle common cases.
+  if (empty() || Ranges.back().getUpper().sle(SubRange.getLower())) {
+    return;
+  }
+  if (SubRange.getUpper().sle(Ranges.front().getLower())) {
+    return;
+  }
+
+  SmallVector<ConstantRange, 2> Result;
+  auto AppendRange = [&Result](APInt Start, APInt End) {
+    if (Start.slt(End))
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jvoung wrote:

might be helpful to have brief comment "append new range if not empty" (was initially less clear why the slt check)

https://github.com/llvm/llvm-project/pull/97093