nir/opt_offsets: fix try_extract_const_addition recursion

This initially looks like a miscompilation bug, but I don't think it's
actually possible for it to create incorrect code.

fossil-db (Sienna Cichlid):
Totals from 32 (0.02% of 134572) affected shaders:
VGPRs: 1336 -> 1320 (-1.20%)
CodeSize: 90552 -> 89468 (-1.20%)
Instrs: 17007 -> 16852 (-0.91%); split: -0.92%, +0.01%
Latency: 429040 -> 428136 (-0.21%); split: -0.21%, +0.00%
InvThroughput: 84966 -> 84572 (-0.46%); split: -0.47%, +0.00%
Copies: 1458 -> 1468 (+0.69%); split: -0.07%, +0.75%
Branches: 382 -> 384 (+0.52%)
PreSGPRs: 970 -> 968 (-0.21%)
PreVGPRs: 1029 -> 1011 (-1.75%)

Signed-off-by: Rhys Perry <pendingchaos02@gmail.com>
Reviewed-by: Emma Anholt <emma@anholt.net>
Reviewed-by: Timur Kristóf <timur.kristof@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/14009>

diff --git a/src/compiler/nir/nir_opt_offsets.c b/src/compiler/nir/nir_opt_offsets.c
index 88b7b2a..9e1ae25 100644 (file)
--- a/src/compiler/nir/nir_opt_offsets.c
+++ b/src/compiler/nir/nir_opt_offsets.c
@@ -70,7 +70,7 @@ try_extract_const_addition(nir_builder *b, nir_instr *instr, opt_offsets_state *
          return alu->src[1 - i].src.ssa;
       }
 
-      nir_ssa_def *replace_src = try_extract_const_addition(b, alu->src[0].src.ssa->parent_instr, state, out_const);
+      nir_ssa_def *replace_src = try_extract_const_addition(b, alu->src[i].src.ssa->parent_instr, state, out_const);
       if (replace_src) {
          b->cursor = nir_before_instr(&alu->instr);
          return nir_iadd(b, replace_src, alu->src[1 - i].src.ssa);