Mesa (master): gm107/ir: prevent WaW hazards in instruction scheduling

[Ilia Mirkin]

Module: Mesa
Branch: master
Commit: 57e721a45693e510c6ec25b37ec0ccd23d434553
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=57e721a45693e510c6ec25b37ec0ccd23d434553

Author: Rhys Perry <pendingchaos02 at gmail.com>
Date:   Sat May 19 22:03:39 2018 +0100

gm107/ir: prevent WaW hazards in instruction scheduling

Previously, findFirstUse() only considered reads "uses". This fixes that
by making it check both an instruction's sources and definitions. It
also shortens both findFistUse() and findFirstDef() along the way.

Reviewed-by: Ilia Mirkin <imirkin at alum.mit.edu>

---

 .../drivers/nouveau/codegen/nv50_ir_emit_gm107.cpp | 111 +++++++++++----------
 1 file changed, 57 insertions(+), 54 deletions(-)

diff --git a/src/gallium/drivers/nouveau/codegen/nv50_ir_emit_gm107.cpp b/src/gallium/drivers/nouveau/codegen/nv50_ir_emit_gm107.cpp
index 1f6189890c..26826d6360 100644
--- a/src/gallium/drivers/nouveau/codegen/nv50_ir_emit_gm107.cpp
+++ b/src/gallium/drivers/nouveau/codegen/nv50_ir_emit_gm107.cpp
@@ -3618,6 +3618,7 @@ private:
 
    bool insertBarriers(BasicBlock *);
 
+   bool doesInsnWriteTo(const Instruction *insn, const Value *val) const;
    Instruction *findFirstUse(const Instruction *) const;
    Instruction *findFirstDef(const Instruction *) const;
 
@@ -3948,8 +3949,48 @@ SchedDataCalculatorGM107::needWrDepBar(const Instruction *insn) const
    return false;
 }
 
-// Find the next instruction inside the same basic block which uses the output
-// of the given instruction in order to avoid RaW hazards.
+// Helper function for findFirstUse() and findFirstDef()
+bool
+SchedDataCalculatorGM107::doesInsnWriteTo(const Instruction *insn,
+                                          const Value *val) const
+{
+   if (val->reg.file != FILE_GPR &&
+       val->reg.file != FILE_PREDICATE &&
+       val->reg.file != FILE_FLAGS)
+      return false;
+
+   for (int d = 0; insn->defExists(d); ++d) {
+      const Value* def = insn->getDef(d);
+      int minGPR = def->reg.data.id;
+      int maxGPR = minGPR + def->reg.size / 4 - 1;
+
+      if (def->reg.file != val->reg.file)
+         continue;
+
+      if (def->reg.file == FILE_GPR) {
+         if (val->reg.data.id + val->reg.size / 4 - 1 < minGPR ||
+             val->reg.data.id > maxGPR)
+            continue;
+         return true;
+      } else
+      if (def->reg.file == FILE_PREDICATE) {
+         if (val->reg.data.id != minGPR)
+            continue;
+         return true;
+      } else
+      if (def->reg.file == FILE_FLAGS) {
+         if (val->reg.data.id != minGPR)
+            continue;
+         return true;
+      }
+   }
+
+   return false;
+}
+
+// Find the next instruction inside the same basic block which uses (reads or
+// writes from) the output of the given instruction in order to avoid RaW and
+// WaW hazards.
 Instruction *
 SchedDataCalculatorGM107::findFirstUse(const Instruction *bari) const
 {
@@ -3961,34 +4002,13 @@ SchedDataCalculatorGM107::findFirstUse(const Instruction *bari) const
    for (insn = bari->next; insn != NULL; insn = next) {
       next = insn->next;
 
-      for (int s = 0; insn->srcExists(s); ++s) {
-         const Value *src = insn->src(s).rep();
-         for (int d = 0; bari->defExists(d); ++d) {
-            const ValueDef &def = bari->def(d);
-            int minGPR = def.rep()->reg.data.id;
-            int maxGPR = minGPR + def.rep()->reg.size / 4 - 1;
-
-            if (def.getFile() == FILE_GPR) {
-               if (insn->src(s).getFile() != FILE_GPR ||
-                   src->reg.data.id + src->reg.size / 4 - 1 < minGPR ||
-                   src->reg.data.id > maxGPR)
-                  continue;
-               return insn;
-            } else
-            if (def.getFile() == FILE_PREDICATE) {
-               if (insn->src(s).getFile() != FILE_PREDICATE ||
-                   src->reg.data.id != minGPR)
-                  continue;
-               return insn;
-            }
-            if (def.getFile() == FILE_FLAGS) {
-               if (insn->src(s).getFile() != FILE_FLAGS ||
-                   src->reg.data.id != minGPR)
-                  continue;
-               return insn;
-            }
-         }
-      }
+      for (int s = 0; insn->srcExists(s); ++s)
+         if (doesInsnWriteTo(bari, insn->getSrc(s)))
+            return insn;
+
+      for (int d = 0; insn->defExists(d); ++d)
+         if (doesInsnWriteTo(bari, insn->getDef(d)))
+            return insn;
    }
    return NULL;
 }
@@ -3999,34 +4019,16 @@ Instruction *
 SchedDataCalculatorGM107::findFirstDef(const Instruction *bari) const
 {
    Instruction *insn, *next;
-   int minGPR, maxGPR;
+
+   if (!bari->srcExists(0))
+      return NULL;
 
    for (insn = bari->next; insn != NULL; insn = next) {
       next = insn->next;
 
-      for (int d = 0; insn->defExists(d); ++d) {
-         const Value *def = insn->def(d).rep();
-         if (insn->def(d).getFile() != FILE_GPR &&
-             insn->def(d).getFile() != FILE_FLAGS)
-            continue;
-
-         minGPR = def->reg.data.id;
-         maxGPR = minGPR + def->reg.size / 4 - 1;
-
-         for (int s = 0; bari->srcExists(s); ++s) {
-            const Value *src = bari->src(s).rep();
-            if (bari->src(s).getFile() == FILE_FLAGS &&
-                insn->def(d).getFile() == FILE_FLAGS &&
-                src->reg.data.id == minGPR)
-               return insn;
-            if (bari->src(s).getFile() != FILE_GPR ||
-                insn->def(d).getFile() != FILE_GPR ||
-                src->reg.data.id + src->reg.size / 4 - 1 < minGPR ||
-                src->reg.data.id > maxGPR)
-               continue;
+      for (int s = 0; bari->srcExists(s); ++s)
+         if (doesInsnWriteTo(insn, bari->getSrc(s)))
             return insn;
-         }
-      }
    }
    return NULL;
 }
@@ -4084,7 +4086,8 @@ SchedDataCalculatorGM107::insertBarriers(BasicBlock *bb)
       if (need_wr_bar) {
          // When the instruction requires to emit a write dependency barrier
          // (all which write something at a variable latency), find the next
-         // instruction which reads the outputs.
+         // instruction which reads the outputs (or writes to them, potentially
+         // completing before this insn.
          usei = findFirstUse(insn);
 
          // Allocate and emit a new barrier.