From bef0601d51a95f0032ec63f708bba523db4c9325 Mon Sep 17 00:00:00 2001
From: Faith Ekstrand <faith.ekstrand@collabora.com>
Date: Tue, 19 Mar 2024 08:28:55 -0500
Subject: [PATCH] nir/lower_reg: Remove dead reg_decl intrinsics
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For any reg we can lower, we remove it whenever we remove the last read
or write.  For regs that aren't used at all, however, there are no reads
or writes so there's nothing to trigger the removal.  Instead, we need
to do it in setup_reg.

Reviewed-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Reviewed-by: Daniel Schürmann <daniel@schuermann.dev>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/28300>
---
 src/compiler/nir/nir_lower_reg_intrinsics_to_ssa.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/src/compiler/nir/nir_lower_reg_intrinsics_to_ssa.c b/src/compiler/nir/nir_lower_reg_intrinsics_to_ssa.c
index b844f4e5b82..fd1305ff464 100644
--- a/src/compiler/nir/nir_lower_reg_intrinsics_to_ssa.c
+++ b/src/compiler/nir/nir_lower_reg_intrinsics_to_ssa.c
@@ -36,6 +36,11 @@ struct regs_to_ssa_state {
 static void
 setup_reg(nir_intrinsic_instr *decl, struct regs_to_ssa_state *state)
 {
+   if (nir_def_is_unused(&decl->def)) {
+      nir_instr_remove(&decl->instr);
+      return;
+   }
+
    assert(state->values[decl->def.index] == NULL);
    if (!should_lower_reg(decl))
       return;