[Mesa-dev] [PATCH 2/2] nvc0/ir: replace cvt instructions with add to improve shader performance

[Karol Herbst]

gives me an performance boost of 0.2% in pixmark_piano on my gk106, gm204 and
gp107.

changes in shader-db:

total instructions in shared programs     : 7614782 -> 7614782 (0.00%)
total cvt instructions in shared programs : 139343 -> 95856 (-31.21%)
total gprs used in shared programs        : 798045 -> 798045 (0.00%)
total shared used in shared programs      : 639636 -> 639636 (0.00%)
total local used in shared programs       : 24648 -> 24648 (0.00%)
total bytes used in shared programs       : 81330696 -> 81330696 (0.00%)

                local     shared        gpr       inst       cvts      bytes
    helped          0          0          0          0      14037          0
      hurt          0          0          0          0          0          0

Signed-off-by: Karol Herbst <kherbst at redhat.com>
---
 .../nouveau/codegen/nv50_ir_lowering_nvc0.cpp | 55 +++++++++++++++++++
 .../nouveau/codegen/nv50_ir_lowering_nvc0.h   |  1 +
 2 files changed, 56 insertions(+)

diff --git a/src/gallium/drivers/nouveau/codegen/nv50_ir_lowering_nvc0.cpp b/src/gallium/drivers/nouveau/codegen/nv50_ir_lowering_nvc0.cpp
index 295497be2f9..267fef0898d 100644
--- a/src/gallium/drivers/nouveau/codegen/nv50_ir_lowering_nvc0.cpp
+++ b/src/gallium/drivers/nouveau/codegen/nv50_ir_lowering_nvc0.cpp
@@ -719,6 +719,58 @@ NVC0LegalizePostRA::propagateJoin(BasicBlock *bb)
    bb->remove(bb->getEntry());
 }
 
+// replaces instructions which would end up as f2f or i2i with faster
+// alternatives:
+//  - abs(a)     -> add(0, abs a)
+//  - neg(a)     -> add(0, neg a)
+//  - neg(abs a) -> add(0, neg abs a)
+//  - sat(a)     -> sat add(0, a)
+void
+NVC0LegalizePostRA::replaceCvt(Instruction *cvt)
+{
+   if (typeSizeof(cvt->sType) == 8)
+      return;
+   if (cvt->sType != cvt->dType)
+      return;
+   // we could make it work, but in this case we have optimizations disabled
+   // and we don't really care either way.
+   if (cvt->src(0).getFile() == FILE_IMMEDIATE)
+      return;
+
+   switch (cvt->op) {
+   case OP_ABS:
+      if (cvt->src(0).mod)
+         break;
+      if (!isFloatType(cvt->sType))
+         break;
+      cvt->op = OP_ADD;
+      cvt->moveSources(0, 1);
+      cvt->src(1).mod = NV50_IR_MOD_ABS;
+      cvt->setSrc(0, rZero);
+      cvt->src(0).mod = 0;
+      break;
+   case OP_NEG:
+      if (cvt->src(0).mod && (cvt->src(0).mod.neg() || !isFloatType(cvt->sType)))
+         break;
+      cvt->op = OP_ADD;
+      cvt->moveSources(0, 1);
+      cvt->src(1).mod = cvt->src(0).mod ? NV50_IR_MOD_NEG_ABS : NV50_IR_MOD_NEG;
+      cvt->setSrc(0, rZero);
+      cvt->src(0).mod = 0;
+      break;
+   case OP_SAT:
+      if (cvt->src(0).mod)
+         break;
+      cvt->op = OP_ADD;
+      cvt->moveSources(0, 1);
+      cvt->setSrc(0, rZero);
+      cvt->saturate = true;
+      break;
+   default:
+      break;
+   }
+}
+
 bool
 NVC0LegalizePostRA::visit(BasicBlock *bb)
 {
@@ -758,6 +810,9 @@ NVC0LegalizePostRA::visit(BasicBlock *bb)
                next = hi;
          }
 
+         if (i->isCvt())
+            replaceCvt(i);
+
          if (i->op != OP_MOV && i->op != OP_PFETCH)
             replaceZero(i);
       }
diff --git a/src/gallium/drivers/nouveau/codegen/nv50_ir_lowering_nvc0.h b/src/gallium/drivers/nouveau/codegen/nv50_ir_lowering_nvc0.h
index e0f50ab0904..4679c56471b 100644
--- a/src/gallium/drivers/nouveau/codegen/nv50_ir_lowering_nvc0.h
+++ b/src/gallium/drivers/nouveau/codegen/nv50_ir_lowering_nvc0.h
@@ -81,6 +81,7 @@ private:
    virtual bool visit(Function *);
    virtual bool visit(BasicBlock *);
 
+   void replaceCvt(Instruction *);
    void replaceZero(Instruction *);
    bool tryReplaceContWithBra(BasicBlock *);
    void propagateJoin(BasicBlock *);
-- 
2.19.2