[Mesa-dev] [PATCH] i965/vs: fix unit mismatch in base_offset.

[Paul Berry]

Callers of emit_scratch_{read,write}() pass a base_offset that is
measured in bytes, but emit_scratch_{read,write}() was assuming it was
measured in multiples of a complete register.  As a result, a shader
using a scratch read/write offset greater than zero (in practice, a
shader containing more than one variable in scratch) would use too
large an offset, frequently exceeding the available scratch space.

This patch corrects the mismatch by dividing base_offset by REG_SIZE
at the beginning of emit_scratch_{read,write}().

NOTE: This is a candidate for stable release branches.
---

No test cases were failing because of this bug, but it was getting in
the way of Ken's efforts to implement register spilling for vertex
shaders.

Ken: I've done a full piglit run on master to verify that it doesn't
regress anything, but I didn't check whether there are any remaining
regressions when I apply it to your "spilling" branch.  All I checked
was that it fixed the 3 regressions you told me about earlier today.

 src/mesa/drivers/dri/i965/brw_vec4_visitor.cpp | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/src/mesa/drivers/dri/i965/brw_vec4_visitor.cpp b/src/mesa/drivers/dri/i965/brw_vec4_visitor.cpp
index 682837f..60fab54 100644
--- a/src/mesa/drivers/dri/i965/brw_vec4_visitor.cpp
+++ b/src/mesa/drivers/dri/i965/brw_vec4_visitor.cpp
@@ -2443,12 +2443,19 @@ vec4_visitor::get_pull_constant_offset(vec4_instruction *inst,
 /**
  * Emits an instruction before @inst to load the value named by @orig_src
  * from scratch space at @base_offset to @temp.
+ *
+ * @base_offset is measured in bytes.
  */
 void
 vec4_visitor::emit_scratch_read(vec4_instruction *inst,
 				dst_reg temp, src_reg orig_src,
 				int base_offset)
 {
+   /* Convert base_offset from bytes to a register number, since that's what
+    * get_scratch_offset() expects.
+    */
+   base_offset /= REG_SIZE;
+
    int reg_offset = base_offset + orig_src.reg_offset;
    src_reg index = get_scratch_offset(inst, orig_src.reladdr, reg_offset);
 
@@ -2458,12 +2465,19 @@ vec4_visitor::emit_scratch_read(vec4_instruction *inst,
 /**
  * Emits an instruction after @inst to store the value to be written
  * to @orig_dst to scratch space at @base_offset, from @temp.
+ *
+ * @base_offset is measured in bytes.
  */
 void
 vec4_visitor::emit_scratch_write(vec4_instruction *inst,
 				 src_reg temp, dst_reg orig_dst,
 				 int base_offset)
 {
+   /* Convert base_offset from bytes to a register number, since that's what
+    * get_scratch_offset() expects.
+    */
+   base_offset /= REG_SIZE;
+
    int reg_offset = base_offset + orig_dst.reg_offset;
    src_reg index = get_scratch_offset(inst, orig_dst.reladdr, reg_offset);
 
-- 
1.7.12