[SCEV] Fix potentially empty set for unsigned ranges

The following commit enabled the analysis of ranges for heap allocations:
22ca38d

The range turns out to be empty in cases such as the one in test (which
is [1,1)), leading to an assertion failure. This patch fixes for the
same case.

Fixes llvm#63856

Reviewed By: fhahn

Differential Revision: https://reviews.llvm.org/D159160

Author: tejas-amd

llvm/lib/Analysis/ScalarEvolution.cpp

@@ -6843,7 +6843,7 @@ const ConstantRange &ScalarEvolution::getRangeRef(
         if (llvm::isKnownNonZero(V, DL))
           MinVal = Align;
         ConservativeResult = ConservativeResult.intersectWith(
-            {MinVal, MaxVal + 1}, RangeType);
+            ConstantRange::getNonEmpty(MinVal, MaxVal + 1), RangeType);
       }
     }
 

llvm/test/Analysis/ScalarEvolution/malloc.ll

@@ -23,4 +23,15 @@ define ptr @f2() {
   ret ptr %alloc
 }
 
+define ptr @undefined_max() {
+; CHECK-LABEL: 'undefined_max'
+; CHECK-NEXT:  Classifying expressions for: @undefined_max
+; CHECK-NEXT:    %alloc = call nonnull ptr @malloc(i64 -1)
+; CHECK-NEXT:    -->  %alloc U: full-set S: full-set
+; CHECK-NEXT:  Determining loop execution counts for: @undefined_max
+;
+  %alloc = call nonnull ptr @malloc(i64 -1)
+  ret ptr %alloc
+}
+
 declare noalias noundef ptr @malloc(i64 noundef) allockind("alloc,uninitialized") allocsize(0)