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>

diff --git a/src/gallium/drivers/nouveau/codegen/nv50_ir.cpp b/src/gallium/drivers/nouveau/codegen/nv50_ir.cpp
index b96f919..6f12df7 100644 (file)
--- 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 7e4e193..2448c73 100644 (file)
--- 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;