[llvm] [ValueTracking][RISCV] Use ConstantRange::getUnsignedMax instead of getUpper to simplify some code. (PR #96816)

[Craig Topper via llvm-commits]

https://github.com/topperc created https://github.com/llvm/llvm-project/pull/96816

This avoids the need to subtract 1 and explain why.

>From 995f0c6281499bd1ad739bc398cc3753ba3bf929 Mon Sep 17 00:00:00 2001
From: Craig Topper <craig.topper at sifive.com>
Date: Wed, 26 Jun 2024 13:26:14 -0700
Subject: [PATCH] [ValueTracking][RISCV] Use ConstantRange::getUnsignedMax
 instead of getUpper to simplify some code.

This avoids the need to subtract 1 and explain why.
---
 llvm/lib/Analysis/ValueTracking.cpp | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
index 777b2792a1ed2..1dfc6cfac4551 100644
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -1740,10 +1740,8 @@ static void computeKnownBitsFromOperator(const Operator *I,
             cast<ConstantInt>(II->getArgOperand(HasAVL))->getZExtValue());
         RISCVII::VLMUL VLMUL = static_cast<RISCVII::VLMUL>(
             cast<ConstantInt>(II->getArgOperand(1 + HasAVL))->getZExtValue());
-        // The Range is [Lower, Upper), so we need to subtract 1 here to get the
-        // real upper value.
         uint64_t MaxVLEN =
-            (Range.getUpper().getZExtValue() - 1) * RISCV::RVVBitsPerBlock;
+            Range.getUnsignedMax().getZExtValue() * RISCV::RVVBitsPerBlock;
         uint64_t MaxVL = MaxVLEN / RISCVVType::getSEWLMULRatio(SEW, VLMUL);
 
         // Result of vsetvli must be not larger than AVL.