From 3079993727ddfe6b09e1f0ec8f834691fd654b46 Mon Sep 17 00:00:00 2001
From: Ilia Mirkin <imirkin@alum.mit.edu>
Date: Fri, 10 Nov 2017 21:47:59 -0500
Subject: [PATCH] nv50/ir: optimize signed integer modulo by pow-of-2

It's common to use signed int modulo in GLSL. As it happens, the GLSL
specs allow the result to be undefined, but that seems fairly
surprising. It's not that much more effort to get it right, at least for
positive modulo operators.

Signed-off-by: Ilia Mirkin <imirkin@alum.mit.edu>
---
 .../drivers/nouveau/codegen/nv50_ir.cpp       |  8 +----
 .../nouveau/codegen/nv50_ir_peephole.cpp      | 31 +++++++++++++++++--
 2 files changed, 29 insertions(+), 10 deletions(-)

diff --git a/src/gallium/drivers/nouveau/codegen/nv50_ir.cpp b/src/gallium/drivers/nouveau/codegen/nv50_ir.cpp
index b96f9190731..6f12df70a11 100644
--- a/src/gallium/drivers/nouveau/codegen/nv50_ir.cpp
+++ b/src/gallium/drivers/nouveau/codegen/nv50_ir.cpp
@@ -423,13 +423,7 @@ ImmediateValue::isNegative() const
 bool
 ImmediateValue::isPow2() const
 {
-   switch (reg.type) {
-   case TYPE_U8:
-   case TYPE_U16:
-   case TYPE_U32: return util_is_power_of_two(reg.data.u32);
-   default:
-      return false;
-   }
+   return util_is_power_of_two(reg.data.u32);
 }
 
 void
diff --git a/src/gallium/drivers/nouveau/codegen/nv50_ir_peephole.cpp b/src/gallium/drivers/nouveau/codegen/nv50_ir_peephole.cpp
index 7e4e193e3d2..2448c737e73 100644
--- a/src/gallium/drivers/nouveau/codegen/nv50_ir_peephole.cpp
+++ b/src/gallium/drivers/nouveau/codegen/nv50_ir_peephole.cpp
@@ -1054,6 +1054,7 @@ ConstantFolding::opnd(Instruction *i, ImmediateValue &imm0, int s)
          i->op = OP_ADD;
       } else
       if (s == 1 && !imm0.isNegative() && imm0.isPow2() &&
+          !isFloatType(i->dType) &&
           target->isOpSupported(OP_SHLADD, i->dType)) {
          i->op = OP_SHLADD;
          imm0.applyLog2();
@@ -1163,10 +1164,34 @@ ConstantFolding::opnd(Instruction *i, ImmediateValue &imm0, int s)
       break;
 
    case OP_MOD:
-      if (i->sType == TYPE_U32 && imm0.isPow2()) {
+      if (s == 1 && imm0.isPow2()) {
          bld.setPosition(i, false);
-         i->op = OP_AND;
-         i->setSrc(1, bld.loadImm(NULL, imm0.reg.data.u32 - 1));
+         if (i->sType == TYPE_U32) {
+            i->op = OP_AND;
+            i->setSrc(1, bld.loadImm(NULL, imm0.reg.data.u32 - 1));
+         } else if (i->sType == TYPE_S32) {
+            // Do it on the absolute value of the input, and then restore the
+            // sign. The only odd case is MIN_INT, but that should work out
+            // as well, since MIN_INT mod any power of 2 is 0.
+            //
+            // Technically we don't have to do any of this since MOD is
+            // undefined with negative arguments in GLSL, but this seems like
+            // the nice thing to do.
+            Value *abs = bld.mkOp1v(OP_ABS, TYPE_S32, bld.getSSA(), i->getSrc(0));
+            Value *neg, *v1, *v2;
+            bld.mkCmp(OP_SET, CC_LT, TYPE_S32,
+                      (neg = bld.getSSA(1, prog->getTarget()->nativeFile(FILE_PREDICATE))),
+                      TYPE_S32, i->getSrc(0), bld.loadImm(NULL, 0));
+            Value *mod = bld.mkOp2v(OP_AND, TYPE_U32, bld.getSSA(), abs,
+                                    bld.loadImm(NULL, imm0.reg.data.u32 - 1));
+            bld.mkOp1(OP_NEG, TYPE_S32, (v1 = bld.getSSA()), mod)
+               ->setPredicate(CC_P, neg);
+            bld.mkOp1(OP_MOV, TYPE_S32, (v2 = bld.getSSA()), mod)
+               ->setPredicate(CC_NOT_P, neg);
+            newi = bld.mkOp2(OP_UNION, TYPE_S32, i->getDef(0), v1, v2);
+
+            delete_Instruction(prog, i);
+         }
       }
       break;