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nv50/ir/ssa: add a few comments regarding RenamePass

This commit is contained in:
Christoph Bumiller 2013-02-27 15:32:35 +01:00
parent 1535b754fb
commit 1b4faa2b17
1 changed files with 19 additions and 0 deletions
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19
src/gallium/drivers/nv50/codegen/nv50_ir_ssa.cpp
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@ -441,12 +441,21 @@ bool RenamePass::run()
return true;
}
// Go through BBs in dominance order, create new values for each definition,
// and replace all sources with their current new values.
//
// NOTE: The values generated for function inputs/outputs have no connection
// to their corresponding outputs/inputs in other functions. Only allocation
// of physical registers will establish this connection.
//
void RenamePass::search(BasicBlock *bb)
{
LValue *lval, *ssa;
int d, s;
const Target *targ = prog->getTarget();
// Put current definitions for function inputs values on the stack.
// They can be used before any redefinitions are pushed.
if (bb == BasicBlock::get(func->cfg.getRoot())) {
for (std::deque<ValueDef>::iterator it = func->ins.begin();
it != func->ins.end(); ++it) {
@ -463,11 +472,15 @@ void RenamePass::search(BasicBlock *bb)
}
for (Instruction *stmt = bb->getFirst(); stmt; stmt = stmt->next) {
// PHI sources get definitions from the passes through the incident BBs,
// so skip them here.
if (stmt->op != OP_PHI) {
for (s = 0; stmt->srcExists(s); ++s) {
lval = stmt->getSrc(s)->asLValue();
if (!lval)
continue;
// Values on the stack created in previously visited blocks, and
// function inputs, will be valid because they dominate this one.
lval = getStackTop(lval);
if (!lval)
lval = mkUndefined(stmt->getSrc(s));
@ -485,6 +498,7 @@ void RenamePass::search(BasicBlock *bb)
}
}
// Update sources of PHI ops corresponding to this BB in outgoing BBs.
for (Graph::EdgeIterator ei = bb->cfg.outgoing(); !ei.end(); ei.next()) {
Instruction *phi;
int p = 0;
@ -506,9 +520,12 @@ void RenamePass::search(BasicBlock *bb)
}
}
// Visit the BBs we dominate.
for (Graph::EdgeIterator ei = bb->dom.outgoing(); !ei.end(); ei.next())
search(BasicBlock::get(ei.getNode()));
// Update function outputs to the last definitions of their pre-SSA values.
// I hope they're unique, i.e. that we get PHIs for all of them ...
if (bb == BasicBlock::get(func->cfgExit)) {
for (std::deque<ValueRef>::iterator it = func->outs.begin();
it != func->outs.end(); ++it) {
@ -522,6 +539,8 @@ void RenamePass::search(BasicBlock *bb)
}
}
// Pop the values we created in this block from the stack because we will
// return to blocks that we do not dominate.
for (Instruction *stmt = bb->getFirst(); stmt; stmt = stmt->next) {
if (stmt->op == OP_NOP)
continue;