From 55130069b8bbb7abf4de31f4925be9fdfc11101f Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Daniel=20Sch=C3=BCrmann?= <daniel@schuermann.dev>
Date: Mon, 8 Apr 2024 13:47:25 +0200
Subject: [PATCH] aco/vn: copy-propagate trivial phis

Totals from 154 (0.19% of 79395) affected shaders: (GFX11)

Instrs: 102420 -> 101702 (-0.70%); split: -0.71%, +0.01%
CodeSize: 534060 -> 530620 (-0.64%); split: -0.65%, +0.01%
Latency: 560180 -> 559723 (-0.08%); split: -0.10%, +0.01%
InvThroughput: 62769 -> 61708 (-1.69%); split: -1.72%, +0.03%
Copies: 6929 -> 6260 (-9.66%); split: -9.68%, +0.03%
Branches: 1636 -> 1609 (-1.65%)
PreVGPRs: 5913 -> 5906 (-0.12%)
VALU: 52681 -> 52012 (-1.27%); split: -1.27%, +0.00%
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/28661>
---
 src/amd/compiler/aco_opt_value_numbering.cpp | 29 +++++++++++++++-----
 1 file changed, 22 insertions(+), 7 deletions(-)

diff --git a/src/amd/compiler/aco_opt_value_numbering.cpp b/src/amd/compiler/aco_opt_value_numbering.cpp
index 4e3e3548429..4f46f386d69 100644
--- a/src/amd/compiler/aco_opt_value_numbering.cpp
+++ b/src/amd/compiler/aco_opt_value_numbering.cpp
@@ -313,6 +313,21 @@ can_eliminate(aco_ptr<Instruction>& instr)
    return true;
 }
 
+bool
+is_trivial_phi(Block& block, Instruction* instr)
+{
+   if (!is_phi(instr))
+      return false;
+
+   /* Logical LCSSA phis must be kept in order to prevent the optimizer
+    * from doing invalid transformations. */
+   if (instr->opcode == aco_opcode::p_phi && (block.kind & block_kind_loop_exit))
+      return false;
+
+   return std::all_of(instr->operands.begin(), instr->operands.end(),
+                      [&](Operand& op) { return op == instr->operands[0]; });
+}
+
 void
 process_block(vn_ctx& ctx, Block& block)
 {
@@ -333,14 +348,9 @@ process_block(vn_ctx& ctx, Block& block)
           instr->opcode == aco_opcode::p_demote_to_helper || instr->opcode == aco_opcode::p_end_wqm)
          ctx.exec_id++;
 
-      if (!can_eliminate(instr)) {
-         new_instructions.emplace_back(std::move(instr));
-         continue;
-      }
-
       /* simple copy-propagation through renaming */
       bool copy_instr =
-         instr->opcode == aco_opcode::p_parallelcopy ||
+         is_trivial_phi(block, instr.get()) || instr->opcode == aco_opcode::p_parallelcopy ||
          (instr->opcode == aco_opcode::p_create_vector && instr->operands.size() == 1);
       if (copy_instr && !instr->definitions[0].isFixed() && instr->operands[0].isTemp() &&
           instr->operands[0].regClass() == instr->definitions[0].regClass()) {
@@ -348,6 +358,11 @@ process_block(vn_ctx& ctx, Block& block)
          continue;
       }
 
+      if (!can_eliminate(instr)) {
+         new_instructions.emplace_back(std::move(instr));
+         continue;
+      }
+
       instr->pass_flags = ctx.exec_id;
       std::pair<expr_set::iterator, bool> res = ctx.expr_values.emplace(instr.get(), block.index);
 
@@ -388,7 +403,7 @@ void
 rename_phi_operands(Block& block, aco::unordered_map<uint32_t, Temp>& renames)
 {
    for (aco_ptr<Instruction>& phi : block.instructions) {
-      if (phi->opcode != aco_opcode::p_phi && phi->opcode != aco_opcode::p_linear_phi)
+      if (!is_phi(phi))
          break;
 
       for (Operand& op : phi->operands) {