[llvm] [DAG] Improve known bits of Zext/Sext loads with range metadata (PR #80829)

[Matt Arsenault via llvm-commits]

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@@ -3612,32 +3612,42 @@ KnownBits SelectionDAG::computeKnownBits(SDValue Op, const APInt &DemandedElts,
           }
         }
       }
-    } else if (ISD::isZEXTLoad(Op.getNode()) && Op.getResNo() == 0) {
-      // If this is a ZEXTLoad and we are looking at the loaded value.
-      EVT VT = LD->getMemoryVT();
-      unsigned MemBits = VT.getScalarSizeInBits();
-      Known.Zero.setBitsFrom(MemBits);
-    } else if (const MDNode *Ranges = LD->getRanges()) {
-      EVT VT = LD->getValueType(0);
-
-      // TODO: Handle for extending loads
-      if (LD->getExtensionType() == ISD::NON_EXTLOAD) {
+    } else if (Op.getResNo() == 0) {
+      KnownBits Known0(!LD->getMemoryVT().isScalableVT()
+                           ? LD->getMemoryVT().getSizeInBits()
+                           : BitWidth);
+      EVT VT = Op.getValueType();
+      // Fill in any known bits from range information. There are 3 types being
+      // used. The results VT (same vector elt size as BitWidth), the loaded
+      // MemoryVT (which may or may not be vector) and the range VTs original
+      // type. The range matadata needs the full range (i.e
+      // MemoryVT().getSizeInBits()), which is truncated to the correct elt size
+      // if it is know. These are then extended to the original VT sizes below.
+      if (const MDNode *MD = LD->getRanges()) {
+        computeKnownBitsFromRangeMetadata(*MD, Known0);
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arsenm wrote:

But that patch already handles this? The range metadata wouldn't appear in the load node in the first place (unless some other code went out of its way to add it)

https://github.com/llvm/llvm-project/pull/80829