gallivm: avoid crashing in mod by 0 with llvmpipe

This adds code that is basically the same as the code in umod, udiv and idiv.
However, unlike idiv we return -1.

Reviewed-by: Roland Scheidegger <sroland@vmware.com>

diff --git a/src/gallium/auxiliary/gallivm/lp_bld_tgsi_action.c b/src/gallium/auxiliary/gallivm/lp_bld_tgsi_action.c
index 3d5e2cb316b3481cd2a3738045172e6379b9b418..6f75bec5005edf40aef694782a6600426357cf8c 100644 (file)
--- a/src/gallium/auxiliary/gallivm/lp_bld_tgsi_action.c
+++ b/src/gallium/auxiliary/gallivm/lp_bld_tgsi_action.c
@@ -1536,8 +1536,22 @@ mod_emit_cpu(
    struct lp_build_tgsi_context * bld_base,
    struct lp_build_emit_data * emit_data)
 {
-   emit_data->output[emit_data->chan] = lp_build_mod(&bld_base->int_bld,
-                                   emit_data->args[0], emit_data->args[1]);
+   LLVMBuilderRef builder = bld_base->base.gallivm->builder;
+   LLVMValueRef div_mask = lp_build_cmp(&bld_base->uint_bld,
+                                        PIPE_FUNC_EQUAL, emit_data->args[1],
+                                        bld_base->uint_bld.zero);
+   /* We want to make sure that we never divide/mod by zero to not
+    * generate sigfpe. We don't want to crash just because the
+    * shader is doing something weird. */
+   LLVMValueRef divisor = LLVMBuildOr(builder,
+                                      div_mask,
+                                      emit_data->args[1], "");
+   LLVMValueRef result = lp_build_mod(&bld_base->int_bld,
+                                      emit_data->args[0], divisor);
+   /* umod by zero doesn't have a guaranteed return value chose -1 for now. */
+   emit_data->output[emit_data->chan] = LLVMBuildOr(builder,
+                                                    div_mask,
+                                                    result, "");
 }
 
 /* TGSI_OPCODE_NOT */