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i965/vec4: Ignore swizzle of VGRF for use by var_range_end()

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Issue description from Matt's commit e7c376ad:
 "var_range_end(v, n) loops over the n components of variable number v and
  finds the maximum value, giving the last use of any component of v.
  Therefore it expects v to correspond to the variable associated with the
  .x channel of the VGRF.

  var_from_reg() however returns the variable for the first channel of the
  VGRF, post-swizzle.

  So, if the last register had a swizzle with y, z, or w in the swizzle
  component, we would read out of bounds. For any other register, we would
  read liveness information from the next register.

  The fix is to convert the src_reg to a dst_reg in order to call the
  dst_reg version of var_from_reg() that doesn't consider the swizzle."

Closes: #3003
Fixes: 48dfb30f ('intel/compiler: Move all live interval analysis results into vec4_live_variables')
Reviewed-by: Matt Turner <mattst88@gmail.com>
Signed-off-by: Andrii Simiklit <asimiklit.work@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4941>
(cherry picked from commit d1b7462849)
This commit is contained in:
Andrii Simiklit 2020-05-07 12:46:28 +03:00 • committed by Eric Engestrom
parent a366c3f548
commit 2303be5ff1
2 changed files with 2 additions and 2 deletions
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2
.pick_status.json
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@ -2362,7 +2362,7 @@
"description": "i965/vec4: Ignore swizzle of VGRF for use by var_range_end()",
"nominated": true,
"nomination_type": 1,
"resolution": 0,
"resolution": 1,
"master_sha": null,
"because_sha": "48dfb30f9231c22a6af6885dbc9ef86dc2edde1e"
},

2
src/intel/compiler/brw_vec4_cse.cpp
View file

@ -288,7 +288,7 @@ vec4_visitor::opt_cse_local(bblock_t *block, const vec4_live_variables &live)
* more -- a sure sign they'll fail operands_match().
*/
if (src->file == VGRF) {
if (live.var_range_end(var_from_reg(alloc, *src), 8) < ip) {
if (live.var_range_end(var_from_reg(alloc, dst_reg(*src)), 8) < ip) {
entry->remove();
ralloc_free(entry);
break;