[llvm] r339552 - [Tablegen][SubtargetEmitter] Improve expansion of predicates of a variant scheduling class.
Andrea Di Biagio via llvm-commits
llvm-commits at lists.llvm.org
Mon Aug 13 04:09:04 PDT 2018
Author: adibiagio
Date: Mon Aug 13 04:09:04 2018
New Revision: 339552
URL: http://llvm.org/viewvc/llvm-project?rev=339552&view=rev
Log:
[Tablegen][SubtargetEmitter] Improve expansion of predicates of a variant scheduling class.
This patch refactors the logic that expands predicates of a variant scheduling
class.
The idea is to improve the readability of the auto-generated code by removing
redundant parentheses around predicate expressions, and by removing redundant
if(true) statements.
This patch replaces the definition of NoSchedPred in TargetSchedule.td with an
instance of MCSchedPredicate. The new definition is sematically equivalent to
the previous one. The main difference is that now SubtargetEmitter knows that it
represents predicate "true".
Before this patch, we always generated an if (true) for the default transition
of a variant scheduling class.
Example (taken from AArch64GenSubtargetInfo.inc) :
```
if (SchedModel->getProcessorID() == 3) { // CycloneModel
if ((TII->isScaledAddr(*MI)))
return 927; // (WriteIS_WriteLD)_ReadBaseRS
if ((true))
return 928; // WriteLD_ReadDefault
}
```
Extra parentheses were also generated around the predicate expressions.
With this patch, we get the following auto-generated checks:
```
if (SchedModel->getProcessorID() == 3) { // CycloneModel
if (TII->isScaledAddr(*MI))
return 927; // (WriteIS_WriteLD)_ReadBaseRS
return 928; // WriteLD_ReadDefault
}
```
The new auto-generated code behaves exactly the same as before. So, technically
this is a non functional change.
Differential revision: https://reviews.llvm.org/D50566
Modified:
llvm/trunk/include/llvm/Target/TargetSchedule.td
llvm/trunk/utils/TableGen/SubtargetEmitter.cpp
Modified: llvm/trunk/include/llvm/Target/TargetSchedule.td
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/Target/TargetSchedule.td?rev=339552&r1=339551&r2=339552&view=diff
==============================================================================
--- llvm/trunk/include/llvm/Target/TargetSchedule.td (original)
+++ llvm/trunk/include/llvm/Target/TargetSchedule.td Mon Aug 13 04:09:04 2018
@@ -373,7 +373,7 @@ class SchedPredicate<code pred> : SchedP
SchedMachineModel SchedModel = ?;
code Predicate = pred;
}
-def NoSchedPred : SchedPredicate<[{true}]>;
+def NoSchedPred : MCSchedPredicate<TruePred>;
// Associate a predicate with a list of SchedReadWrites. By default,
// the selected SchedReadWrites are still associated with a single
Modified: llvm/trunk/utils/TableGen/SubtargetEmitter.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/utils/TableGen/SubtargetEmitter.cpp?rev=339552&r1=339551&r2=339552&view=diff
==============================================================================
--- llvm/trunk/utils/TableGen/SubtargetEmitter.cpp (original)
+++ llvm/trunk/utils/TableGen/SubtargetEmitter.cpp Mon Aug 13 04:09:04 2018
@@ -1480,30 +1480,54 @@ static void emitPredicateProlog(const Re
}
static void emitPredicates(const CodeGenSchedTransition &T,
- const CodeGenSchedClass &SC,
- PredicateExpander &PE,
+ const CodeGenSchedClass &SC, PredicateExpander &PE,
raw_ostream &OS) {
std::string Buffer;
raw_string_ostream StringStream(Buffer);
formatted_raw_ostream FOS(StringStream);
FOS.PadToColumn(6);
- FOS << "if (";
- for (RecIter RI = T.PredTerm.begin(), RE = T.PredTerm.end(); RI != RE; ++RI) {
- if (RI != T.PredTerm.begin()) {
- FOS << "\n";
- FOS.PadToColumn(8);
- FOS << "&& ";
+
+ auto IsTruePredicate = [](const Record *Rec) {
+ return Rec->isSubClassOf("MCSchedPredicate") &&
+ Rec->getValueAsDef("Pred")->isSubClassOf("MCTrue");
+ };
+
+ // If not all predicates are MCTrue, then we need an if-stmt.
+ unsigned NumNonTruePreds =
+ T.PredTerm.size() - count_if(T.PredTerm, IsTruePredicate);
+ if (NumNonTruePreds) {
+ bool FirstNonTruePredicate = true;
+ for (const Record *Rec : T.PredTerm) {
+ // Skip predicates that evaluate to "true".
+ if (IsTruePredicate(Rec))
+ continue;
+
+ if (FirstNonTruePredicate) {
+ FOS << "if (";
+ FirstNonTruePredicate = false;
+ } else {
+ FOS << "\n";
+ FOS.PadToColumn(8);
+ FOS << "&& ";
+ }
+
+ if (Rec->isSubClassOf("MCSchedPredicate")) {
+ PE.expandPredicate(FOS, Rec->getValueAsDef("Pred"));
+ continue;
+ }
+
+ // Expand this legacy predicate and wrap it around braces if there is more
+ // than one predicate to expand.
+ FOS << ((NumNonTruePreds > 1) ? "(" : "")
+ << Rec->getValueAsString("Predicate")
+ << ((NumNonTruePreds > 1) ? ")" : "");
}
- const Record *Rec = *RI;
- if (Rec->isSubClassOf("MCSchedPredicate"))
- PE.expandPredicate(FOS, Rec->getValueAsDef("Pred"));
- else
- FOS << "(" << Rec->getValueAsString("Predicate") << ")";
+
+ FOS << ")\n"; // end of if-stmt
+ FOS.PadToColumn(8);
}
- FOS << ")\n";
- FOS.PadToColumn(8);
FOS << "return " << T.ToClassIdx << "; // " << SC.Name << '\n';
FOS.flush();
OS << Buffer;
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