[llvm] Use range attribute to constant fold comparisons with constant values. (PR #84627)

[Nikita Popov via llvm-commits]

================
@@ -3729,6 +3729,19 @@ static Value *simplifyICmpWithIntrinsicOnLHS(CmpInst::Predicate Pred,
   }
 }
 
+/// Helper method to get range from metadata or attribute.
+static std::optional<ConstantRange> getRange(Value *V,
+                                             const InstrInfoQuery &IIQ) {
+  if (Instruction *I = dyn_cast<Instruction>(V))
+    if (MDNode *MD = IIQ.getMetadata(I, LLVMContext::MD_range))
+      return getConstantRangeFromMetadata(*MD);
+  if (const Argument *A = dyn_cast<Argument>(V))
----------------
nikic wrote:

We should also check call return values.

Once full support is in place we should probably forbid use of !range of calls.

https://github.com/llvm/llvm-project/pull/84627