[llvm] [RISCV] Track the value range of vsetvlimax (PR #218313)

[Pengcheng Wang via llvm-commits]

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@@ -2903,12 +2897,13 @@ bool llvm::isKnownToBeAPowerOfTwo(const Value *V, bool OrZero,
         if (II->getArgOperand(0) == II->getArgOperand(1))
           return isKnownToBeAPowerOfTwo(II->getArgOperand(0), OrZero, Q, Depth);
         break;
-      case Intrinsic::riscv_vsetvlimax:
-        // VLEN and LMUL are powers of two, and SEW is a power of two.
-        if (ConstantRange Range = getRISCVVSetVLMaxRange(*II);
-            !Range.isFullSet())
-          return OrZero || !Range.contains(APInt(Range.getBitWidth(), 0));
-        return false;
+      case Intrinsic::riscv_vsetvlimax: {
+        // VLMAX is VLEN * LMUL / SEW, which is always a power of two. It can
+        // still be zero for a fractional LMUL with a large SEW and small VLEN
+        // (e.g. e64mf8), so consult the range to rule out zero unless OrZero.
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wangpc-pp wrote:

AI illusion :-)

https://github.com/llvm/llvm-project/pull/218313