Mesa (main): aco/optimizer: Skip SDWA on v_lshlrev when unnecessary in apply_extract.

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Module: Mesa
Branch: main
Commit: ca6ef505ff9b37e4ef8d947ed23fa4f2e44c02f3
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=ca6ef505ff9b37e4ef8d947ed23fa4f2e44c02f3

Author: Timur Kristóf <timur.kristof at gmail.com>
Date:   Thu Sep 30 14:32:07 2021 +0200

aco/optimizer: Skip SDWA on v_lshlrev when unnecessary in apply_extract.

In the following cases:
- lower 16 bits are extracted and the shift amount is 16 or more
- lower 8 bits are extracted and the shift amount is 24 or more
the undesireable upper bits are already shifted out, and therefore
there is no need to add SDWA to the v_lshlrev instruction.

Fossil DB stats on Sienna Cichlid with NGGC on:

Totals from 58239 (45.27% of 128647) affected shaders:
CodeSize: 153498624 -> 153265616 (-0.15%); split: -0.15%, +0.00%
Instrs: 29636304 -> 29578064 (-0.20%); split: -0.20%, +0.00%
Latency: 136931496 -> 136876379 (-0.04%); split: -0.04%, +0.00%
InvThroughput: 21134367 -> 21078861 (-0.26%); split: -0.26%, +0.00%
Copies: 2777550 -> 2777548 (-0.00%); split: -0.00%, +0.00%

Signed-off-by: Timur Kristóf <timur.kristof at gmail.com>
Reviewed-by: Daniel Schürmann <daniel at schuermann.dev>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/13121>

---

 src/amd/compiler/aco_optimizer.cpp | 15 +++++++++++----
 1 file changed, 11 insertions(+), 4 deletions(-)

diff --git a/src/amd/compiler/aco_optimizer.cpp b/src/amd/compiler/aco_optimizer.cpp
index 6773b96eacc..ad70ca15503 100644
--- a/src/amd/compiler/aco_optimizer.cpp
+++ b/src/amd/compiler/aco_optimizer.cpp
@@ -854,6 +854,11 @@ apply_extract(opt_ctx& ctx, aco_ptr<Instruction>& instr, unsigned idx, ssa_info&
    SubdwordSel sel = parse_extract(info.instr);
    assert(sel);
 
+   instr->operands[idx].set16bit(false);
+   instr->operands[idx].set24bit(false);
+
+   ctx.info[tmp.id()].label &= ~label_insert;
+
    if (sel.size() == 4) {
       /* full dword selection */
    } else if (instr->opcode == aco_opcode::v_cvt_f32_u32 && sel.size() == 1 && !sel.sign_extend()) {
@@ -863,6 +868,12 @@ apply_extract(opt_ctx& ctx, aco_ptr<Instruction>& instr, unsigned idx, ssa_info&
       case 2: instr->opcode = aco_opcode::v_cvt_f32_ubyte2; break;
       case 3: instr->opcode = aco_opcode::v_cvt_f32_ubyte3; break;
       }
+   } else if (instr->opcode == aco_opcode::v_lshlrev_b32 && instr->operands[0].isConstant() &&
+              sel.offset() == 0 &&
+              ((sel.size() == 2 && instr->operands[0].constantValue() >= 16u) ||
+               (sel.size() == 1 && instr->operands[0].constantValue() >= 24u))) {
+      /* The undesireable upper bits are already shifted out. */
+      return;
    } else if (can_use_SDWA(ctx.program->chip_class, instr, true) &&
               (tmp.type() == RegType::vgpr || ctx.program->chip_class >= GFX9)) {
       to_SDWA(ctx, instr);
@@ -872,10 +883,6 @@ apply_extract(opt_ctx& ctx, aco_ptr<Instruction>& instr, unsigned idx, ssa_info&
          instr->vop3().opsel |= 1 << idx;
    }
 
-   instr->operands[idx].set16bit(false);
-   instr->operands[idx].set24bit(false);
-
-   ctx.info[tmp.id()].label &= ~label_insert;
    /* label_vopc seems to be the only one worth keeping at the moment */
    for (Definition& def : instr->definitions)
       ctx.info[def.tempId()].label &= label_vopc;