Mesa (main): nir: Add a helper for chasing movs with nir_ssa_scalar().

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Module: Mesa
Branch: main
Commit: 0afab39af9bcf5448d74b9b849c13085fdf92983
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=0afab39af9bcf5448d74b9b849c13085fdf92983

Author: Emma Anholt <emma at anholt.net>
Date:   Fri Jun 25 13:58:04 2021 -0700

nir: Add a helper for chasing movs with nir_ssa_scalar().

Sometimes you might want to find a constant source without going through
all the copy prop and constant folding to make your source be a
load_const.

Reviewed-by: Jason Ekstrand <jason at jlekstrand.net>
Reviewed-by: Alyssa Rosenzweig <alyssa.rosenzweig at collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/11613>

---

 src/compiler/nir/nir.c                    | 41 +++++++++++++++++++++++++++++++
 src/compiler/nir/nir.h                    | 12 +++++++++
 src/compiler/nir/nir_opt_copy_propagate.c | 23 +----------------
 3 files changed, 54 insertions(+), 22 deletions(-)

diff --git a/src/compiler/nir/nir.c b/src/compiler/nir/nir.c
index 70b934e0ce0..b18426a10be 100644
--- a/src/compiler/nir/nir.c
+++ b/src/compiler/nir/nir.c
@@ -2502,3 +2502,44 @@ nir_variable *nir_get_binding_variable(nir_shader *shader, nir_binding binding)
 
    return binding_var;
 }
+
+bool
+nir_alu_instr_is_copy(nir_alu_instr *instr)
+{
+   assert(instr->src[0].src.is_ssa);
+
+   if (instr->op == nir_op_mov) {
+      return !instr->dest.saturate &&
+             !instr->src[0].abs &&
+             !instr->src[0].negate;
+   } else if (nir_op_is_vec(instr->op)) {
+      for (unsigned i = 0; i < instr->dest.dest.ssa.num_components; i++) {
+         if (instr->src[i].abs || instr->src[i].negate)
+            return false;
+      }
+      return !instr->dest.saturate;
+   } else {
+      return false;
+   }
+}
+
+nir_ssa_scalar
+nir_ssa_scalar_chase_movs(nir_ssa_scalar s)
+{
+   while (nir_ssa_scalar_is_alu(s)) {
+      nir_alu_instr *alu = nir_instr_as_alu(s.def->parent_instr);
+      if (!nir_alu_instr_is_copy(alu))
+         break;
+
+      if (alu->op == nir_op_mov) {
+         s.def = alu->src[0].src.ssa;
+         s.comp = alu->src[0].swizzle[s.comp];
+      } else {
+         assert(nir_op_is_vec(alu->op));
+         s.def = alu->src[s.comp].src.ssa;
+         s.comp = alu->src[s.comp].swizzle[0];
+      }
+   }
+
+   return s;
+}
diff --git a/src/compiler/nir/nir.h b/src/compiler/nir/nir.h
index 59e46d05541..99d0f8039c3 100644
--- a/src/compiler/nir/nir.h
+++ b/src/compiler/nir/nir.h
@@ -1457,6 +1457,8 @@ void nir_alu_src_copy(nir_alu_src *dest, const nir_alu_src *src,
 void nir_alu_dest_copy(nir_alu_dest *dest, const nir_alu_dest *src,
                        nir_alu_instr *instr);
 
+bool nir_alu_instr_is_copy(nir_alu_instr *instr);
+
 /* is this source channel used? */
 static inline bool
 nir_alu_instr_channel_used(const nir_alu_instr *instr, unsigned src,
@@ -2614,6 +2616,16 @@ nir_ssa_scalar_chase_alu_src(nir_ssa_scalar s, unsigned alu_src_idx)
    return out;
 }
 
+nir_ssa_scalar nir_ssa_scalar_chase_movs(nir_ssa_scalar s);
+
+/** Returns a nir_ssa_scalar where we've followed the bit-exact mov/vec use chain to the original definition */
+static inline nir_ssa_scalar
+nir_ssa_scalar_resolved(nir_ssa_def *def, unsigned channel)
+{
+   nir_ssa_scalar s = { def, channel };
+   return nir_ssa_scalar_chase_movs(s);
+}
+
 
 typedef struct {
    bool success;
diff --git a/src/compiler/nir/nir_opt_copy_propagate.c b/src/compiler/nir/nir_opt_copy_propagate.c
index 5e5c5fd31bc..386587fa6c8 100644
--- a/src/compiler/nir/nir_opt_copy_propagate.c
+++ b/src/compiler/nir/nir_opt_copy_propagate.c
@@ -56,27 +56,6 @@ is_swizzleless_move(nir_alu_instr *instr)
    return true;
 }
 
-static bool
-is_copy(nir_alu_instr *instr)
-{
-   assert(instr->src[0].src.is_ssa);
-
-   /* we handle modifiers in a separate pass */
-   if (instr->op == nir_op_mov) {
-      return !instr->dest.saturate &&
-             !instr->src[0].abs &&
-             !instr->src[0].negate;
-   } else if (nir_op_is_vec(instr->op)) {
-      for (unsigned i = 0; i < instr->dest.dest.ssa.num_components; i++) {
-         if (instr->src[i].abs || instr->src[i].negate)
-            return false;
-      }
-      return !instr->dest.saturate;
-   } else {
-      return false;
-   }
-}
-
 static bool
 rewrite_to_vec(nir_function_impl *impl, nir_alu_instr *mov, nir_alu_instr *vec)
 {
@@ -162,7 +141,7 @@ copy_prop_instr(nir_function_impl *impl, nir_instr *instr)
 
    nir_alu_instr *mov = nir_instr_as_alu(instr);
 
-   if (!is_copy(mov))
+   if (!nir_alu_instr_is_copy(mov))
       return false;
 
    bool progress = false;