Mesa (staging/20.1): ir_constant: Return zero on out-of-bounds vector accesses

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Module: Mesa
Branch: staging/20.1
Commit: d91921c0d21acdd69795f76a21be786389aafa1c
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=d91921c0d21acdd69795f76a21be786389aafa1c

Author: Danylo Piliaiev <danylo.piliaiev at globallogic.com>
Date:   Mon Aug 17 18:13:24 2020 +0300

ir_constant: Return zero on out-of-bounds vector accesses

Several optimization paths, including constant folding, can lead to
accessing an ir_constant vector with an out of bounds index.

Return 0 since GL_ARB_robustness and GL_KHR_robustness encourage
us to do so.

Fixes piglit tests:
spec at glsl-1.20@execution at vector-out-of-bounds-access@fs-vec4-out-of-bounds-2
spec at glsl-1.20@execution at vector-out-of-bounds-access@fs-vec4-out-of-bounds-4
spec at glsl-1.20@execution at vector-out-of-bounds-access@fs-vec4-out-of-bounds-5

Closes: https://gitlab.freedesktop.org/mesa/mesa/-/issues/2604
CC: <mesa-stable at lists.freedesktop.org>
Signed-off-by: Danylo Piliaiev <danylo.piliaiev at globallogic.com>
Reviewed-by: Eric Anholt <eric at anholt.net>
Reviewed-by: Marcin Ślusarz <marcin.slusarz at intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6363>
(cherry picked from commit e93979ba599355c42df01a89073362b970489a3a)

---

 .pick_status.json        |  2 +-
 src/compiler/glsl/ir.cpp | 14 ++++++++++++++
 2 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/.pick_status.json b/.pick_status.json
index 7921ef3a8a2..8928a5efde6 100644
--- a/.pick_status.json
+++ b/.pick_status.json
@@ -1777,7 +1777,7 @@
         "description": "ir_constant: Return zero on out-of-bounds vector accesses",
         "nominated": true,
         "nomination_type": 0,
-        "resolution": 0,
+        "resolution": 1,
         "master_sha": null,
         "because_sha": null
     },
diff --git a/src/compiler/glsl/ir.cpp b/src/compiler/glsl/ir.cpp
index 922dcd3c819..12faf8e41fc 100644
--- a/src/compiler/glsl/ir.cpp
+++ b/src/compiler/glsl/ir.cpp
@@ -799,6 +799,20 @@ ir_constant::ir_constant(const ir_constant *c, unsigned i)
    this->const_elements = NULL;
    this->type = c->type->get_base_type();
 
+   /* 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.
+    *
+    * GL_KHR_robustness and GL_ARB_robustness encourage us to return zero.
+    */
+   if (i >= c->type->vector_elements) {
+      this->value = { { 0 } };
+      return;
+   }
+
    switch (this->type->base_type) {
    case GLSL_TYPE_UINT:  this->value.u[0] = c->value.u[i]; break;
    case GLSL_TYPE_INT:   this->value.i[0] = c->value.i[i]; break;