Mesa (staging/20.3): aco: fix DCE of rematerializable phi operands

[GitLab Mirror]

Module: Mesa
Branch: staging/20.3
Commit: 539611ace9a17607dff339dbfc160c71906ed845
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=539611ace9a17607dff339dbfc160c71906ed845

Author: Daniel Schürmann <daniel at schuermann.dev>
Date:   Fri Dec 11 14:30:30 2020 +0100

aco: fix DCE of rematerializable phi operands

Otherwise, if a phi gets spilled, the operand might be considered unused.

Fixes: d48d72e98af9436babeeb3a94b312f94bc582b36 ('aco: Initial commit of independent AMD compiler')

Reviewed-by: Rhys Perry <pendingchaos02 at gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/8055>
(cherry picked from commit 0bccfd86f6e97611a3b9b4f227aa414bc3d04e02)

---

 .pick_status.json              |  2 +-
 src/amd/compiler/aco_spill.cpp | 15 +++++++--------
 2 files changed, 8 insertions(+), 9 deletions(-)

diff --git a/.pick_status.json b/.pick_status.json
index dd9464e98e6..60ba003ab96 100644
--- a/.pick_status.json
+++ b/.pick_status.json
@@ -31,7 +31,7 @@
         "description": "aco: fix DCE of rematerializable phi operands",
         "nominated": true,
         "nomination_type": 1,
-        "resolution": 0,
+        "resolution": 1,
         "master_sha": null,
         "because_sha": "d48d72e98af9436babeeb3a94b312f94bc582b36"
     },
diff --git a/src/amd/compiler/aco_spill.cpp b/src/amd/compiler/aco_spill.cpp
index 67c6712e0e4..1abfa04a940 100644
--- a/src/amd/compiler/aco_spill.cpp
+++ b/src/amd/compiler/aco_spill.cpp
@@ -815,6 +815,12 @@ void add_coupling_code(spill_ctx& ctx, Block* block, unsigned block_idx)
           phi->opcode != aco_opcode::p_linear_phi)
          break;
 
+      /* prevent it's definining instruction from being DCE'd if it could be rematerialized */
+      for (const Operand& op : phi->operands) {
+         if (op.isTemp() && ctx.remat.count(op.getTemp()))
+            ctx.remat_used[ctx.remat[op.getTemp()].instr] = true;
+      }
+
       /* if the phi is not spilled, add to instructions */
       if (ctx.spills_entry[block_idx].find(phi->definitions[0].getTemp()) == ctx.spills_entry[block_idx].end()) {
          instructions.emplace_back(std::move(phi));
@@ -1076,14 +1082,7 @@ void process_block(spill_ctx& ctx, unsigned block_idx, Block* block,
    /* phis are handled separetely */
    while (block->instructions[idx]->opcode == aco_opcode::p_phi ||
           block->instructions[idx]->opcode == aco_opcode::p_linear_phi) {
-      aco_ptr<Instruction>& instr = block->instructions[idx];
-      for (const Operand& op : instr->operands) {
-         /* prevent it's definining instruction from being DCE'd if it could be rematerialized */
-         if (op.isTemp() && ctx.remat.count(op.getTemp()))
-            ctx.remat_used[ctx.remat[op.getTemp()].instr] = true;
-      }
-      instructions.emplace_back(std::move(instr));
-      idx++;
+      instructions.emplace_back(std::move(block->instructions[idx++]));
    }
 
    if (block->register_demand.exceeds(ctx.target_pressure))