From: Eric Anholt <eric@anholt.net>
Date: Wed, 16 Mar 2016 01:32:19 +0000 (-0700)
Subject: nir: Optimize out discard_ifs with a constant 0 argument.
X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=1aa8a0392f256a1be8f8d2774a4f7d3e03b3aac3;p=mesa.git

nir: Optimize out discard_ifs with a constant 0 argument.

I found this in a shader that was doing an alpha test when alpha is fixed
at 1.0.

v2: Rebase on master (now the const value is "u32" not "u").

Reviewed-by: Jason Ekstrand <jason@jlekstrand.net> (v1)
---

diff --git a/src/compiler/nir/nir_opt_constant_folding.c b/src/compiler/nir/nir_opt_constant_folding.c
index 8f040619bfa..d6be807b3dc 100644
--- a/src/compiler/nir/nir_opt_constant_folding.c
+++ b/src/compiler/nir/nir_opt_constant_folding.c
@@ -155,6 +155,14 @@ constant_fold_intrinsic_instr(nir_intrinsic_instr *instr)
       progress |= constant_fold_deref(&instr->instr, instr->variables[i]);
    }
 
+   if (instr->intrinsic == nir_intrinsic_discard_if) {
+      nir_const_value *src_val = nir_src_as_const_value(instr->src[0]);
+      if (src_val && src_val->u32[0] == 0) {
+         nir_instr_remove(&instr->instr);
+         progress = true;
+      }
+   }
+
    return progress;
 }