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[ConstraintElimination] Negate IR condition directly. 

Instead of using ConstraintSystem::negate when adding new constraints,
flip the condition in IR.

The main advantage is that EQ predicates can be represented by 2
constraints, which makes negating based on the constraint tricky. The IR
condition can easily negated.
This commit is contained in:
Florian Hahn 2021-01-28 13:41:21 +00:00
parent f0ffc690d5
commit ce190e4144
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GPG Key ID: 61D7554B5CECDC0D
1 changed files with 17 additions and 2 deletions
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19
llvm/lib/Transforms/Scalar/ConstraintElimination.cpp
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@ -13,6 +13,7 @@
#include "llvm/Transforms/Scalar/ConstraintElimination.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/ScopeExit.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Analysis/ConstraintSystem.h"
@ -336,6 +337,22 @@ static bool eliminateConstraints(Function &F, DominatorTree &DT) {
continue;
}
// Set up a function to restore the predicate at the end of the scope if it
// has been negated. Negate the predicate in-place, if required.
auto *CI = dyn_cast<CmpInst>(CB.Condition);
auto PredicateRestorer = make_scope_exit([CI, &CB]() {
if (CB.Not && CI)
CI->setPredicate(CI->getInversePredicate());
});
if (CB.Not) {
if (CI) {
CI->setPredicate(CI->getInversePredicate());
} else {
LLVM_DEBUG(dbgs() << "Can only negate compares so far.\n");
continue;
}
}
// Otherwise, add the condition to the system and stack, if we can transform
// it into a constraint.
auto R = getConstraint(CB.Condition, Value2Index, true);
@ -343,8 +360,6 @@ static bool eliminateConstraints(Function &F, DominatorTree &DT) {
continue;
LLVM_DEBUG(dbgs() << "Adding " << *CB.Condition << " " << CB.Not << "\n");
if (CB.Not)
R = ConstraintSystem::negate(R);
// If R has been added to the system, queue it for removal once it goes
// out-of-scope.