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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>
This commit is contained in:
Ilia Mirkin 2017-11-10 21:47:59 -05:00
parent 676761252b
commit 3079993727
2 changed files with 29 additions and 10 deletions
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8
src/gallium/drivers/nouveau/codegen/nv50_ir.cpp
View File

@ -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

31
src/gallium/drivers/nouveau/codegen/nv50_ir_peephole.cpp
View File

@ -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;