nir: get rid of OOB dereferences in nir_lower_io_arrays_to_elements
This patch fixes mesa compiler crash in i965 on shaders like the following one:
```
in VS_OUTPUT {
mat4 data;
} vs_output;
out vec4 fs_output;
vec4 convert(in float val) {
return vec4(val);
}
void main()
{
fs_output = vec4(0.0);
for (int a = -1; a < 5; a++) {
for (int b = -1; b < 5; b++) {
fs_output += convert(vs_output.data[b][a]);
}
}
}
```
Section 5.11 (Out-of-Bounds Accesses) of the GLSL 4.60 spec says:
In the subsections described above for array, vector, matrix and
structure accesses, any out-of-bounds access produced undefined
behavior....
Out-of-bounds reads return undefined values, which
include values from other variables of the active program or zero.
Out-of-bounds writes may be discarded or overwrite
other variables of the active program.
GL_KHR_robustness and GL_ARB_robustness encourage us to return zero
for reads.
Reviewed-by: Rhys Perry <pendingchaos02@gmail.com>
Signed-off-by: Andrii Simiklit <andrii.simiklit@globallogic.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6560>
diff --git a/src/compiler/nir/nir_lower_io_arrays_to_elements.c b/src/compiler/nir/nir_lower_io_arrays_to_elements.c
index 3763265..2603667 100644
--- a/src/compiler/nir/nir_lower_io_arrays_to_elements.c
+++ b/src/compiler/nir/nir_lower_io_arrays_to_elements.c
@@ -115,6 +115,18 @@
{
b->cursor = nir_before_instr(&intr->instr);
+ if (nir_deref_instr_is_known_out_of_bounds(nir_src_as_deref(intr->src[0]))) {
+ /* See Section 5.11 (Out-of-Bounds Accesses) of the GLSL 4.60 */
+ if (intr->intrinsic != nir_intrinsic_store_deref) {
+ nir_ssa_def *zero = nir_imm_zero(b, intr->dest.ssa.num_components,
+ intr->dest.ssa.bit_size);
+ nir_ssa_def_rewrite_uses(&intr->dest.ssa,
+ nir_src_for_ssa(zero));
+ }
+ nir_instr_remove(&intr->instr);
+ return;
+ }
+
nir_variable **elements =
get_array_elements(varyings, var, b->shader->info.stage);
