st/glsl_to_tgsi: avoid iterating past the head of the instruction list

exec_node::get_prev() does not guard against going past the beginning
of the list, so we need to add explicit checks here.

Found by ASAN in piglit arb_shader_storage_buffer_object-rendering.

Cc: mesa-stable@lists.freedesktop.org
Signed-off-by: Marek Olšák <marek.olsak@amd.com>

diff --git a/src/mesa/state_tracker/st_glsl_to_tgsi.cpp b/src/mesa/state_tracker/st_glsl_to_tgsi.cpp
index d43d821aad0317b909b7673916e56679124df572..af41bdbbea10d622824823a8d516e3de597d858a 100644 (file)
--- a/src/mesa/state_tracker/st_glsl_to_tgsi.cpp
+++ b/src/mesa/state_tracker/st_glsl_to_tgsi.cpp
@@ -3611,10 +3611,17 @@ glsl_to_tgsi_visitor::visit_ssbo_intrinsic(ir_call *ir)
       inst->resource = buffer;
       if (access)
          inst->buffer_access = access->value.u[0];
+
+      if (inst == this->instructions.get_head_raw())
+         break;
       inst = (glsl_to_tgsi_instruction *)inst->get_prev();
-      if (inst->op == TGSI_OPCODE_UADD)
+
+      if (inst->op == TGSI_OPCODE_UADD) {
+         if (inst == this->instructions.get_head_raw())
+            break;
          inst = (glsl_to_tgsi_instruction *)inst->get_prev();
-   } while (inst && inst->op == op && inst->resource.file == PROGRAM_UNDEFINED);
+      }
+   } while (inst->op == op && inst->resource.file == PROGRAM_UNDEFINED);
 }
 
 void