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authorKristian Høgsberg Kristensen <[email protected]>2015-11-04 14:58:54 -0800
committerKristian Høgsberg Kristensen <[email protected]>2015-11-10 12:02:46 -0800
commit96b22fb080894ba1840af2372f28a46cc0f40c76 (patch)
tree197f2454ecfd1778eeea2d81146682ff35fce01e /src/mapi/mapi.c
parent60dd5287ff8dbbbe0dbe76bdff6d13c7a5ea9ef0 (diff)
glsl: Use array deref for access to vector components
We've assumed that we could lower per-component vector access from vec[i] = scalar to vec = ir_triop_vector_insert(vec, scalar, i) but with SSBOs (and compute shader SLM and tesselation outputs) this is no longer valid. If a vector is "externally visible", multiple threads can write independent components simultaneously. With lowering to ir_triop_vector_insert, each thread read the entire vector, changes one component, then writes out the entire vector. This is racy. Instead of generating a ir_binop_vector_extract when we see v[i], we generate ir_dereference_array. We then add a lowering pass to lower the ir_dereference_array to ir_binop_vector_extract for rvalues and for to vector_insert for lvalues in a separate lowering pass. The resulting IR is the same as before, but we now have a window between ast->ir conversion and the lowering pass where v[i] appears in the IR as an array deref. This lets us run lowering passes that lower the vector access to I/O (eg for SSBO load/store) before we lower the per-component access to full vector writes. Reviewed-by: Jordan Justen <[email protected]> Signed-off-by: Kristian Høgsberg Kristensen <[email protected]>
Diffstat (limited to 'src/mapi/mapi.c')
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