From e573440a5d53fdee01d9b931e498e8b2acf50916 Mon Sep 17 00:00:00 2001
From: M Henning <drawoc@darkrefraction.com>
Date: Sun, 5 Jun 2022 23:01:09 -0400
Subject: [PATCH] nv50_ir_ra: Don't coalesce mixed constraints

It's difficult to handle nodes that have both fixed reg constraints and
compMasks. We may be able to handle some of these in the future, but
skip them for now.

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/24541>
---
 .../drivers/nouveau/codegen/nv50_ir_ra.cpp    | 40 +++++++++++++++----
 1 file changed, 33 insertions(+), 7 deletions(-)

diff --git a/src/gallium/drivers/nouveau/codegen/nv50_ir_ra.cpp b/src/gallium/drivers/nouveau/codegen/nv50_ir_ra.cpp
index a0d56218107..3a81b3b57cd 100644
--- a/src/gallium/drivers/nouveau/codegen/nv50_ir_ra.cpp
+++ b/src/gallium/drivers/nouveau/codegen/nv50_ir_ra.cpp
@@ -852,6 +852,37 @@ GCRA::coalesceValues(Value *dst, Value *src, bool force)
    LValue *rep = dst->join->asLValue();
    LValue *val = src->join->asLValue();
 
+   // Don't do anything if already coalesced
+   if (rep == val)
+      return false;
+
+   // Check if coalesced value would be overconstrained
+   bool skip_copy_compound = false;
+   if (!force) {
+      int num_constraints = 0;
+
+      if (rep->compound) num_constraints++;
+      if (val->compound) num_constraints++;
+
+      if (rep->compound && val->compound &&
+          rep->compMask == val->compMask) {
+         num_constraints--;
+         skip_copy_compound = true;
+      }
+
+      if (rep->reg.data.id >= 0) num_constraints++;
+      if (val->reg.data.id >= 0) num_constraints++;
+
+      if (rep->reg.data.id >= 0 && val->reg.data.id >= 0 &&
+          rep->reg.data.id == val->reg.data.id) {
+         num_constraints--;
+      }
+
+      if (num_constraints > 1) {
+         return false;
+      }
+   }
+
    if (!force && val->reg.data.id >= 0) {
       rep = src->join->asLValue();
       val = dst->join->asLValue();
@@ -872,8 +903,7 @@ GCRA::coalesceValues(Value *dst, Value *src, bool force)
          if (val->reg.data.id >= 0)
             WARN("forced coalescing of values in different fixed regs !\n");
       } else {
-         if (val->reg.data.id >= 0)
-            return false;
+         assert(val->reg.data.id < 0);
          // make sure that there is no overlap with the fixed register of rep
          for (ArrayList::Iterator it = func->allLValues.iterator();
               !it.end(); it.next()) {
@@ -888,14 +918,10 @@ GCRA::coalesceValues(Value *dst, Value *src, bool force)
    if (!force && nRep->livei.overlaps(nVal->livei))
       return false;
 
-   // TODO: Handle this case properly.
-   if (!force && rep->compound && val->compound)
-      return false;
-
    INFO_DBG(prog->dbgFlags, REG_ALLOC, "joining %%%i($%i) <- %%%i\n",
             rep->id, rep->reg.data.id, val->id);
 
-   if (!force)
+   if (!force && !skip_copy_compound)
       copyCompound(dst, src);
 
    // set join pointer of all values joined with val