Mesa (master): nvc0/ir: fix collection of first uses for texture barrier insertion

[Ilia Mirkin]

Module: Mesa
Branch: master
Commit: a2af42c1d2dc91f4c31e25ff9fff15a89a9b6ead
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=a2af42c1d2dc91f4c31e25ff9fff15a89a9b6ead

Author: Ilia Mirkin <imirkin at alum.mit.edu>
Date:   Fri Jun 12 16:09:05 2015 +0200

nvc0/ir: fix collection of first uses for texture barrier insertion

One of the places we have to insert texbars is in situations where the
result of the tex gets overwritten by a different instruction (e.g. in a
conditional statement). However in some situations it can actually
appear as though the original tex itself is an overwriting instruction.
This can naturally never really happen, so just ignore the tex
instruction when it comes up.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=90347
Signed-off-by: Ilia Mirkin <imirkin at alum.mit.edu>
Cc: "10.5 10.6" <mesa-stable at lists.freedesktop.org>

---

 .../drivers/nouveau/codegen/nv50_ir_lowering_nvc0.cpp  |   16 +++++++++++-----
 1 file changed, 11 insertions(+), 5 deletions(-)

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 411e2de..7a5d1ce 100644
--- a/src/gallium/drivers/nouveau/codegen/nv50_ir_lowering_nvc0.cpp
+++ b/src/gallium/drivers/nouveau/codegen/nv50_ir_lowering_nvc0.cpp
@@ -168,7 +168,7 @@ NVC0LegalizePostRA::insnDominatedBy(const Instruction *later,
 
 void
 NVC0LegalizePostRA::addTexUse(std::list<TexUse> &uses,
-                              Instruction *usei, const Instruction *insn)
+                              Instruction *usei, const Instruction *texi)
 {
    bool add = true;
    for (std::list<TexUse>::iterator it = uses.begin();
@@ -183,7 +183,7 @@ NVC0LegalizePostRA::addTexUse(std::list<TexUse> &uses,
          ++it;
    }
    if (add)
-      uses.push_back(TexUse(usei, insn));
+      uses.push_back(TexUse(usei, texi));
 }
 
 void
@@ -195,7 +195,8 @@ NVC0LegalizePostRA::findOverwritingDefs(const Instruction *texi,
    while (insn->op == OP_MOV && insn->getDef(0)->equals(insn->getSrc(0)))
       insn = insn->getSrc(0)->getUniqueInsn();
 
-   if (!insn->bb->reachableBy(texi->bb, term))
+   // NOTE: the tex itself is, of course, not an overwriting definition
+   if (insn == texi || !insn->bb->reachableBy(texi->bb, term))
       return;
 
    switch (insn->op) {
@@ -243,7 +244,12 @@ NVC0LegalizePostRA::findFirstUses(
          visited.insert(usei);
 
          if (usei->op == OP_PHI || usei->op == OP_UNION) {
-            // need a barrier before WAW cases
+            // need a barrier before WAW cases, like:
+            //   %r0 = tex
+            //   if ...
+            //     texbar <- is required or tex might replace x again
+            //     %r1 = x <- overwriting def
+            //   %r2 = phi %r0, %r1
             for (int s = 0; usei->srcExists(s); ++s) {
                Instruction *defi = usei->getSrc(s)->getUniqueInsn();
                if (defi && &usei->src(s) != *u)
@@ -262,7 +268,7 @@ NVC0LegalizePostRA::findFirstUses(
              usei->subOp != NV50_IR_SUBOP_MOV_FINAL) {
             findFirstUses(texi, usei, uses, visited);
          } else {
-            addTexUse(uses, usei, insn);
+            addTexUse(uses, usei, texi);
          }
       }
    }