nvc0/ir: remove merge/split pairs to allow normal propagation to occur

Because the TGSI interface creates merges for each instruction source
and then splits them back out, there are a lot of unnecessary
merge/split pairs which do essentially nothing. The various modifier/etc
propagation doesn't know how to walk though those, so just remove them
when they're unnecessary.

Signed-off-by: Ilia Mirkin <imirkin@alum.mit.edu>

diff --git a/src/gallium/drivers/nouveau/codegen/nv50_ir_peephole.cpp b/src/gallium/drivers/nouveau/codegen/nv50_ir_peephole.cpp
index 62d2ef75f4668fe97e2a770affc467f0519509b7..6a4ea4ed6e8a1d857a0ca9d741c3160675023292 100644 (file)
--- a/src/gallium/drivers/nouveau/codegen/nv50_ir_peephole.cpp
+++ b/src/gallium/drivers/nouveau/codegen/nv50_ir_peephole.cpp
@@ -118,6 +118,35 @@ CopyPropagation::visit(BasicBlock *bb)
 
 // =============================================================================
 
+class MergeSplits : public Pass
+{
+private:
+   virtual bool visit(BasicBlock *);
+};
+
+// For SPLIT / MERGE pairs that operate on the same registers, replace the
+// post-merge def with the SPLIT's source.
+bool
+MergeSplits::visit(BasicBlock *bb)
+{
+   Instruction *i, *next, *si;
+
+   for (i = bb->getEntry(); i; i = next) {
+      next = i->next;
+      if (i->op != OP_MERGE || typeSizeof(i->dType) != 8)
+         continue;
+      si = i->getSrc(0)->getInsn();
+      if (si->op != OP_SPLIT || si != i->getSrc(1)->getInsn())
+         continue;
+      i->def(0).replace(si->getSrc(0), false);
+      delete_Instruction(prog, i);
+   }
+
+   return true;
+}
+
+// =============================================================================
+
 class LoadPropagation : public Pass
 {
 private:
@@ -2662,6 +2691,7 @@ Program::optimizeSSA(int level)
 {
    RUN_PASS(1, DeadCodeElim, buryAll);
    RUN_PASS(1, CopyPropagation, run);
+   RUN_PASS(1, MergeSplits, run);
    RUN_PASS(2, GlobalCSE, run);
    RUN_PASS(1, LocalCSE, run);
    RUN_PASS(2, AlgebraicOpt, run);