nv50/ir: allow OP_SET to merge with OP_SET_AND/etc as well as a neg

This covers the pattern where a KILL_IF is used, which triggers a
comparison of -x to 0. This can usually be folded into the comparison whose
result is being compared to 0, however it may, itself, have already been
combined with another comparison. That shouldn't impact the logic of
this pass however. With this and the & 1.0 change, code like

00000020: 001c0001 80081df4     set b32 $r0 lt f32 $r0 0x3e800000
00000028: 001c0000 201fc000     and b32 $r0 $r0 0x3f800000
00000030: 7f9c001e dd885c00     set $p0 0x1 lt f32 neg $r0 0x0
00000038: 0000003c 19800000     $p0 discard

becomes

00000020: 001c001d b5881df4     set $p0 0x1 lt f32 $r0 0x3e800000
00000028: 0000003c 19800000     $p0 discard

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

src/gallium/drivers/nouveau/codegen/nv50_ir_peephole.cpp

@@ -278,7 +278,6 @@ private:
 
    void tryCollapseChainedMULs(Instruction *, const int s, ImmediateValue&);
 
-   // TGSI 'true' is converted to -1 by F2I(NEG(SET)), track back to SET
    CmpInstruction *findOriginForTestWithZero(Value *);
 
    unsigned int foldCount;
@@ -337,25 +336,33 @@ ConstantFolding::findOriginForTestWithZero(Value *value)
       return NULL;
    Instruction *insn = value->getInsn();
 
-   while (insn && insn->op != OP_SET) {
-      Instruction *next = NULL;
-      switch (insn->op) {
-      case OP_NEG:
-      case OP_ABS:
-      case OP_CVT:
-         next = insn->getSrc(0)->getInsn();
-         if (insn->sType != next->dType)
+   if (insn->asCmp() && insn->op != OP_SLCT)
+      return insn->asCmp();
+
+   /* Sometimes mov's will sneak in as a result of other folding. This gets
+    * cleaned up later.
+    */
+   if (insn->op == OP_MOV)
+      return findOriginForTestWithZero(insn->getSrc(0));
+
+   /* Deal with AND 1.0 here since nv50 can't fold into boolean float */
+   if (insn->op == OP_AND) {
+      int s = 0;
+      ImmediateValue imm;
+      if (!insn->src(s).getImmediate(imm)) {
+         s = 1;
+         if (!insn->src(s).getImmediate(imm))
             return NULL;
-         break;
-      case OP_MOV:
-         next = insn->getSrc(0)->getInsn();
-         break;
-      default:
-         return NULL;
       }
-      insn = next;
+      if (imm.reg.data.f32 != 1.0f)
+         return NULL;
+      /* TODO: Come up with a way to handle the condition being inverted */
+      if (insn->src(!s).mod != Modifier(0))
+         return NULL;
+      return findOriginForTestWithZero(insn->getSrc(!s));
    }
-   return insn ? insn->asCmp() : NULL;
+
+   return NULL;
 }
 
 void
@@ -946,29 +953,51 @@ ConstantFolding::opnd(Instruction *i, ImmediateValue &imm0, int s)
 
    case OP_SET: // TODO: SET_AND,OR,XOR
    {
+      /* This optimizes the case where the output of a set is being compared
+       * to zero. Since the set can only produce 0/-1 (int) or 0/1 (float), we
+       * can be a lot cleverer in our comparison.
+       */
       CmpInstruction *si = findOriginForTestWithZero(i->getSrc(t));
       CondCode cc, ccZ;
-      if (i->src(t).mod != Modifier(0))
-         return;
-      if (imm0.reg.data.u32 != 0 || !si || si->op != OP_SET)
+      if (imm0.reg.data.u32 != 0 || !si)
          return;
       cc = si->setCond;
       ccZ = (CondCode)((unsigned int)i->asCmp()->setCond & ~CC_U);
+      // We do everything assuming var (cmp) 0, reverse the condition if 0 is
+      // first.
       if (s == 0)
          ccZ = reverseCondCode(ccZ);
+      // If there is a negative modifier, we need to undo that, by flipping
+      // the comparison to zero.
+      if (i->src(t).mod.neg())
+         ccZ = reverseCondCode(ccZ);
+      // If this is a signed comparison, we expect the input to be a regular
+      // boolean, i.e. 0/-1. However the rest of the logic assumes that true
+      // is positive, so just flip the sign.
+      if (i->sType == TYPE_S32) {
+         assert(!isFloatType(si->dType));
+         ccZ = reverseCondCode(ccZ);
+      }
       switch (ccZ) {
-      case CC_LT: cc = CC_FL; break;
-      case CC_GE: cc = CC_TR; break;
-      case CC_EQ: cc = inverseCondCode(cc); break;
-      case CC_LE: cc = inverseCondCode(cc); break;
-      case CC_GT: break;
-      case CC_NE: break;
+      case CC_LT: cc = CC_FL; break; // bool < 0 -- this is never true
+      case CC_GE: cc = CC_TR; break; // bool >= 0 -- this is always true
+      case CC_EQ: cc = inverseCondCode(cc); break; // bool == 0 -- !bool
+      case CC_LE: cc = inverseCondCode(cc); break; // bool <= 0 -- !bool
+      case CC_GT: break; // bool > 0 -- bool
+      case CC_NE: break; // bool != 0 -- bool
       default:
          return;
       }
+
+      // Update the condition of this SET to be identical to the origin set,
+      // but with the updated condition code. The original SET should get
+      // DCE'd, ideally.
+      i->op = si->op;
       i->asCmp()->setCond = cc;
       i->setSrc(0, si->src(0));
       i->setSrc(1, si->src(1));
+      if (si->srcExists(2))
+         i->setSrc(2, si->src(2));
       i->sType = si->sType;
    }
       break;