[mlir][intrange] Fix inference of zero-trip loop bound (#96429)

When lower bound and exclusive upper bound of a loop are the same, and
the zero-trip loop is not canonicalized away before the analysis, this
leads to a meaningless range for the induction variable being inferred.
This patch adds a check to make sure that the inferred range for the IV
is meaningful before updating the analysis state.

Fix #94423

Author: ubfx

mlir/lib/Analysis/DataFlow/IntegerRangeAnalysis.cpp

@@ -195,9 +195,14 @@ void IntegerRangeAnalysis::visitNonControlFlowArguments(
       max -= 1;
     }
 
-    IntegerValueRangeLattice *ivEntry = getLatticeElement(*iv);
-    auto ivRange = ConstantIntRanges::fromSigned(min, max);
-    propagateIfChanged(ivEntry, ivEntry->join(IntegerValueRange{ivRange}));
+    // If we infer the lower bound to be larger than the upper bound, the
+    // resulting range is meaningless and should not be used in further
+    // inferences.
+    if (max.sge(min)) {
+      IntegerValueRangeLattice *ivEntry = getLatticeElement(*iv);
+      auto ivRange = ConstantIntRanges::fromSigned(min, max);
+      propagateIfChanged(ivEntry, ivEntry->join(IntegerValueRange{ivRange}));
+    }
     return;
   }
 

mlir/test/Dialect/Arith/int-range-interface.mlir

@@ -918,3 +918,21 @@ func.func @test_cmpf_propagates(%a: f32, %b: f32) -> index {
   func.return %2 : index
 }
 
+// CHECK-LABEL: func @zero_trip_loop
+func.func @zero_trip_loop() {
+  %idx1 = arith.constant 1 : index
+  scf.for %arg0 = %idx1 to %idx1 step %idx1 {
+    %138 = index.floordivs %arg0, %arg0
+  }
+  return
+}
+
+// CHECK-LABEL: func @zero_trip_loop2
+func.func @zero_trip_loop2() {
+  %idx1 = arith.constant 1 : index
+  %idxm1 = arith.constant -1 : index
+  scf.for %arg0 = %idx1 to %idx1 step %idxm1 {
+    %138 = index.floordivs %arg0, %arg0
+  }
+  return
+}