[Analysis] Clamp SelectOp divisibility when condConstancy reduces output contiguity

lib/Analysis/AxisInfo.cpp

@@ -960,8 +960,12 @@ class SelectOpAxisInfoVisitor final : public AxisInfoVisitorImpl<OpTy> {
                                   rhsInfo.getConstancy(d), condConstancy[d]));
           contiguity.push_back(gcd(lhsInfo.getContiguity(d),
                                    rhsInfo.getContiguity(d), condConstancy[d]));
+          // getDivisibilityFromContiguity does not see condConstancy; clamp
+          // by the just-computed output contiguity so the result remains
+          // sound when condConstancy reduces it below the input contiguities.
           divisibility.push_back(
-              getDivisibilityFromContiguity(lhsInfo, rhsInfo, d));
+              gcd(getDivisibilityFromContiguity(lhsInfo, rhsInfo, d),
+                  contiguity.back()));
         }
       }
       if (lhsInfo.getConstantValue().has_value() &&

test/Analysis/test-alignment.mlir

@@ -1146,6 +1146,24 @@ tt.func @select_same_value_constancy() {
 
 // -----
 
+// Regression: SelectOp must clamp divisibility when condConstancy reduces the
+// output contiguity below either input's contiguity. Otherwise the helper
+// getDivisibilityFromContiguity overestimates divisibility because it does not
+// see condConstancy. See issue triton-lang/triton#10067.
+tt.func @select_cond_constancy_clamps_divisibility(%arg0: tensor<8xi1>) {
+  // expected-remark @below {{contiguity = [8], divisibility = [8], constancy = [1], constant_value = <none>}}
+  %lhs = tt.make_range {end = 16 : i32, start = 8 : i32} : tensor<8xi32>
+  // expected-remark @below {{contiguity = [8], divisibility = [16], constancy = [1], constant_value = <none>}}
+  %rhs = tt.make_range {end = 24 : i32, start = 16 : i32} : tensor<8xi32>
+  // %arg0 has unknown contents, so condConstancy = 1. Output contiguity must
+  // collapse to gcd(8, 8, 1) = 1; divisibility must clamp to 1 (not gcd(8, 16) = 8).
+  // expected-remark @below {{contiguity = [1], divisibility = [1], constancy = [1], constant_value = <none>}}
+  %sel = arith.select %arg0, %lhs, %rhs : tensor<8xi1>, tensor<8xi32>
+  tt.return
+}
+
+// -----
+
 tt.func @cmp_after_max_constancy() {
   %c5 = arith.constant dense<5> : tensor<4xi32>
   %c7 = arith.constant dense<7> : tensor<4xi32>