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nv50/ir: fix Instruction::isActionEqual for PHI instructions

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phi instructions don't have the same results by simply having the same sources.
They need to be inside the same BasicBlock or share an equal condition
resulting into a path through the shader selecting equal sources as well.

short example:

cond = ...;
const0 = 0;
const1 = 1;

if (cond) {
  ssa_1 = const0;
} else {
  ssa_2 = const1;
}
ssa_3 = phi ssa_1 ssa_2;

if (!cond) {
  ssa_4 = const0;
} else {
  ssa_5 = const1;
}
ssa_6 = phi ssa_4 ssa_5;

allthough both phis actually have sources with equal results, merging them
would be wrong due to having a different condition selecting which source to
take.

For now we also stick an assert into GlobalCSE, because it should never end up
having to merge phi instructions.

Reviewed-by: Ilia Mirkin <imirkin@alum.mit.edu>
This commit is contained in:
Karol Herbst 2018-06-28 18:55:00 +02:00
parent f2cc694d8e
commit de13978733
1 changed files with 6 additions and 0 deletions
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6
src/gallium/drivers/nouveau/codegen/nv50_ir_peephole.cpp
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@ -3472,6 +3472,11 @@ Instruction::isActionEqual(const Instruction *that) const
} else
if (this->asFlow()) {
return false;
} else
if (this->op == OP_PHI && this->bb != that->bb) {
/* TODO: we could probably be a bit smarter here by following the
* control flow, but honestly, it is quite painful to check */
return false;
} else {
if (this->ipa != that->ipa ||
this->lanes != that->lanes ||
@ -3568,6 +3573,7 @@ GlobalCSE::visit(BasicBlock *bb)
break;
}
if (!phi->srcExists(s)) {
assert(ik->op != OP_PHI);
Instruction *entry = bb->getEntry();
ik->bb->remove(ik);
if (!entry || entry->op != OP_JOIN)