Created attachment 67277 [details]
Test case to trigger assertion

Problem:

The attached test case triggers the following assertion during GLSL to TGSI lowering:

../../src/mesa/state_tracker/st_glsl_to_tgsi.cpp:673:get_opcode: Assertion `op != 177' failed.

Explanation:

The following GLSL IR fragment arises from the test case:

(expression int % (expression int u2i (swiz x (txf uvec4 (var_ref S)  (constant int (0))  0  (constant int (0)) ))) (constant int (0))

glsl_to_tgsi_visitor::visit(ir_texture *ir) sets the temporary register holding the TXF result to type glsl::vec4_type. This was correct prior to GL_EXT_texture_integer, which introduced texelFetch(usampler2D) and texelFetch(isampler2D) with return types uvec4 and ivec4 respectively.

The incorrect vec4 type propagates further through the lowering process. The inconsistency between this type and its ir_binop_mod consumer eventually triggers the assertion.

Solution:

It appears to be safe to use ir_texture->type, which carries the correct texelFetch return type, instead of glsl_type::vec4.

The attached patch resolves the issue for me. However, it has not been subjected to regression testing.