glsl: Rework lowering of non-constant array indexing
The previous implementation could easily get tricked if the LHS of an assignment included a non-constant index that was "inside" another dereference. For example: mat4 m[2]; m[0][i] = vec4(0.0); Due to the way it tracked whether the array was being assigned, it would think that the non-constant index was in an r-value. The new code fixes that by tracking l-values and r-values differently. The index is also replaced by cloning the IR and replacing the index variable instead of the odd way it was done before. v2: Apply some simplifications suggested by Eric Anholt. Making assignment_generator::rvalue be ir_dereference instead of ir_rvalue simplified the code a bit. Fixes i965 piglit fs-temp-array-mat[234]-index-wr and vs-varying-array-mat[234]-index-wr. Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=34691 Reviewed-by:Eric Anholt <eric@anholt.net> (cherry picked from commit 1731ac30) To make bisects work, this also squashes in: glsl: Correctly return progress from lower_variable_index_to_cond_assign lower_variable_index_to_cond_assign runs until it can't make any more progress. It then returns the result of the last pass which will always be false. This caused the lowering loop in _mesa_ir_link_shader to end before doing one last round of lower_if_to_cond_assign. This caused several if-statements (resulting from lower_variable_index_to_cond_assign) to be left in the IR. In addition to this change, lower_variable_index_to_cond_assign should take a flag indicating whether or not it should even generate if-statements. This is easily controlled by switch_generator::linear_sequence_max_length. This would generate much better code on architectures without any flow contol. Fixes i915 piglit regressions glsl-texcoord-array and glsl-fs-vec4-indexing-temp-src. Reviewed-by:
Eric Anholt <eric@anholt.net> (cherry picked from commit c1e591ee)
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