[llvm] [GlobalISel] Add iterative known-bits evaluation to GISelValueTracking (PR #221755)

[via llvm-commits]

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@@ -1138,6 +1138,77 @@ void GISelValueTracking::computeKnownBitsImpl(Register R, KnownBits &Known,
   LLVM_DEBUG(dumpResult(MI, Known, Depth));
 }
 
+static void genUnknown(MachineRegisterInfo &MRI, const Register &Reg,
+                       KnownBits &Known) {
+  LLT Ty = MRI.getType(Reg);
+  if (!Ty.isValid()) {
+    Known = KnownBits();
+    return;
+  }
+  unsigned BitWidth = Ty.getScalarSizeInBits();
+  Known = KnownBits(BitWidth);
+}
+
+/// Evaluate a known-bits query with an explicit worklist instead of recursive
+/// descent.
+void GISelValueTracking::computeKnownBitsImpl(Register R, KnownBits &Known,
+                                              const APInt &DemandedElts,
+                                              unsigned Depth) {
+  const bool TopLevel = Stack.empty();
+
+  // Nested queries only consult the per-query cache. If the result is not
+  // available yet, enqueue the request and return an unknown placeholder.
+  if (!TopLevel) {
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daemonpilot wrote:

Done. Removed `TopLevel` and replaced `!Stack.empty()` directly.

https://github.com/llvm/llvm-project/pull/221755