[llvm] [InstCombine] Improve `foldICmpUsingKnownBits` by using ConstantRange info (PR #76252)

[Yingwei Zheng via llvm-commits]

https://github.com/dtcxzyw created https://github.com/llvm/llvm-project/pull/76252

None

>From 60e97c5846e24db3321c5526844f8558375cd86a Mon Sep 17 00:00:00 2001
From: Yingwei Zheng <dtcxzyw2333 at gmail.com>
Date: Sat, 23 Dec 2023 00:24:04 +0800
Subject: [PATCH] [InstCombine] Improve `foldICmpUsingKnownBits` by using
 ConstantRange info

---
 .../InstCombine/InstCombineCompares.cpp       | 28 +++++++++++++------
 1 file changed, 20 insertions(+), 8 deletions(-)

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
index 289976718e52f3..18e725bcca1fbf 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
@@ -6131,18 +6131,30 @@ Instruction *InstCombinerImpl::foldICmpUsingKnownBits(ICmpInst &I) {
   // Given the known and unknown bits, compute a range that the LHS could be
   // in.  Compute the Min, Max and RHS values based on the known bits. For the
   // EQ and NE we use unsigned values.
+  bool IsSigned = I.isSigned();
+  ConstantRange::PreferredRangeType RangeType =
+      IsSigned ? ConstantRange::Signed : ConstantRange::Unsigned;
+  ConstantRange Op0CR = ConstantRange::fromKnownBits(Op0Known, IsSigned);
+  if (Ty->isIntOrIntVectorTy())
+    Op0CR.intersectWith(
+        computeConstantRange(Op0, IsSigned, SQ.IIQ.UseInstrInfo), RangeType);
+  ConstantRange Op1CR = ConstantRange::fromKnownBits(Op1Known, IsSigned);
+  if (Ty->isIntOrIntVectorTy())
+    Op1CR.intersectWith(
+        computeConstantRange(Op1, IsSigned, SQ.IIQ.UseInstrInfo), RangeType);
+
   APInt Op0Min(BitWidth, 0), Op0Max(BitWidth, 0);
   APInt Op1Min(BitWidth, 0), Op1Max(BitWidth, 0);
   if (I.isSigned()) {
-    Op0Min = Op0Known.getSignedMinValue();
-    Op0Max = Op0Known.getSignedMaxValue();
-    Op1Min = Op1Known.getSignedMinValue();
-    Op1Max = Op1Known.getSignedMaxValue();
+    Op0Min = Op0CR.getSignedMin();
+    Op0Max = Op0CR.getSignedMax();
+    Op1Min = Op1CR.getSignedMin();
+    Op1Max = Op1CR.getSignedMax();
   } else {
-    Op0Min = Op0Known.getMinValue();
-    Op0Max = Op0Known.getMaxValue();
-    Op1Min = Op1Known.getMinValue();
-    Op1Max = Op1Known.getMaxValue();
+    Op0Min = Op0CR.getUnsignedMin();
+    Op0Max = Op0CR.getUnsignedMax();
+    Op1Min = Op1CR.getUnsignedMin();
+    Op1Max = Op1CR.getUnsignedMax();
   }
 
   // If Min and Max are known to be the same, then SimplifyDemandedBits figured