[LoadStoreConversion] Handle negative indices in boundary checks (#3429)

Fixes #3240

---------

Signed-off-by: dchigarev <[email protected]>

Author: dchigarev

third_party/intel/lib/TritonIntelGPUToLLVM/LoadStoreOpToLLVM.cpp

@@ -263,8 +263,11 @@ struct LoadStoreConversionBase {
             {blockPtr.begin() + blockShape, blockPtr.begin() + blockStride},
             b.int_val(1, 1),
             [&](const Value &index, const Value &shape, const Value &mask) {
-              // mask = mask && (index < shape)
-              return b.and_(b.icmp_slt(index, b.trunc(i32_ty, shape)), mask);
+              // mask = mask && (index < shape) && idx >= 0
+              auto is_pos_idx = b.icmp_sge(index, b.int_val(32, 0));
+              return b.and_(
+                  b.and_(b.icmp_slt(index, b.trunc(i32_ty, shape)), mask),
+                  is_pos_idx);
             }));
       }
     }