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-rw-r--r--mesalib/src/glsl/lower_vec_index_to_swizzle.cpp22
1 files changed, 20 insertions, 2 deletions
diff --git a/mesalib/src/glsl/lower_vec_index_to_swizzle.cpp b/mesalib/src/glsl/lower_vec_index_to_swizzle.cpp
index c7630c28a..46fd6ace1 100644
--- a/mesalib/src/glsl/lower_vec_index_to_swizzle.cpp
+++ b/mesalib/src/glsl/lower_vec_index_to_swizzle.cpp
@@ -33,6 +33,7 @@
#include "ir_visitor.h"
#include "ir_optimization.h"
#include "glsl_types.h"
+#include "main/macros.h"
/**
* Visitor class for replacing expressions with ir_constant values.
@@ -76,8 +77,25 @@ ir_vec_index_to_swizzle_visitor::convert_vec_index_to_swizzle(ir_rvalue *ir)
void *ctx = ralloc_parent(ir);
this->progress = true;
- return new(ctx) ir_swizzle(deref->array,
- ir_constant->value.i[0], 0, 0, 0, 1);
+
+ /* Page 40 of the GLSL 1.20 spec says:
+ *
+ * "When indexing with non-constant expressions, behavior is undefined
+ * if the index is negative, or greater than or equal to the size of
+ * the vector."
+ *
+ * The quoted spec text mentions non-constant expressions, but this code
+ * operates on constants. These constants are the result of non-constant
+ * expressions that have been optimized to constants. The common case here
+ * is a loop counter from an unrolled loop that is used to index a vector.
+ *
+ * The ir_swizzle constructor gets angry if the index is negative or too
+ * large. For simplicity sake, just clamp the index to [0, size-1].
+ */
+ const int i = MIN2(MAX2(ir_constant->value.i[0], 0),
+ (deref->array->type->vector_elements - 1));
+
+ return new(ctx) ir_swizzle(deref->array, i, 0, 0, 0, 1);
}
ir_visitor_status