RPCS3/llvm-mirror
1
0
Fork 0
mirror of https://github.com/RPCS3/llvm-mirror.git synced 2025-01-31 12:41:49 +01:00
Code Issues Projects Releases Wiki Activity

[SCEV] Limited support for unsigned preds in isImpliedViaOperations

Browse Source 
The logic there only considers `SLT/SGT` predicates. We can use the same logic
for proving `ULT/UGT` predicates if all involved values are non-negative.

Adding full-scale support for unsigned might be challenging because of code amount,
so we can consider this in the future.

Differential Revision: https://reviews.llvm.org/D88087
Reviewed By: reames
This commit is contained in:
Max Kazantsev 2020-10-02 10:20:06 +07:00
parent 4bb7568ead
commit a15cdde064
2 changed files with 55 additions and 4 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

26
lib/Analysis/ScalarEvolution.cpp
View File

@ -10236,13 +10236,31 @@ bool ScalarEvolution::isImpliedViaOperations(ICmpInst::Predicate Pred,
// We want to avoid hurting the compile time with analysis of too big trees.
if (Depth > MaxSCEVOperationsImplicationDepth)
return false;
// We only want to work with ICMP_SGT comparison so far.
// TODO: Extend to ICMP_UGT?
if (Pred == ICmpInst::ICMP_SLT) {
Pred = ICmpInst::ICMP_SGT;
// We only want to work with GT comparison so far.
if (Pred == ICmpInst::ICMP_ULT || Pred == ICmpInst::ICMP_SLT) {
Pred = CmpInst::getSwappedPredicate(Pred);
std::swap(LHS, RHS);
std::swap(FoundLHS, FoundRHS);
}
// For unsigned, try to reduce it to corresponding signed comparison.
if (Pred == ICmpInst::ICMP_UGT)
// We can replace unsigned predicate with its signed counterpart if all
// involved values are non-negative.
// TODO: We could have better support for unsigned.
if (isKnownNonNegative(FoundLHS) && isKnownNonNegative(FoundRHS)) {
// Knowing that both FoundLHS and FoundRHS are non-negative, and knowing
// FoundLHS >u FoundRHS, we also know that FoundLHS >s FoundRHS. Let us
// use this fact to prove that LHS and RHS are non-negative.
const SCEV *MinusOne = getNegativeSCEV(getOne(LHS->getType()));
if (isImpliedCondOperands(ICmpInst::ICMP_SGT, LHS, MinusOne, FoundLHS,
FoundRHS) &&
isImpliedCondOperands(ICmpInst::ICMP_SGT, RHS, MinusOne, FoundLHS,
FoundRHS))
Pred = ICmpInst::ICMP_SGT;
}
if (Pred != ICmpInst::ICMP_SGT)
return false;

33
unittests/Analysis/ScalarEvolutionTest.cpp
View File

@ -1283,4 +1283,37 @@ TEST_F(ScalarEvolutionsTest, ImpliedViaAddRecStart) {
});
}
TEST_F(ScalarEvolutionsTest, UnsignedIsImpliedViaOperations) {
LLVMContext C;
SMDiagnostic Err;
std::unique_ptr<Module> M =
parseAssemblyString("define void @foo(i32* %p1, i32* %p2) { "
"entry: "
" %x = load i32, i32* %p1, !range !0 "
" %cond = icmp ne i32 %x, 0 "
" br i1 %cond, label %guarded, label %exit "
"guarded: "
" %y = add i32 %x, -1 "
" ret void "
"exit: "
" ret void "
"} "
"!0 = !{i32 0, i32 2147483647}",
Err, C);
ASSERT_TRUE(M && "Could not parse module?");
ASSERT_TRUE(!verifyModule(*M) && "Must have been well formed!");
runWithSE(*M, "foo", [](Function &F, LoopInfo &LI, ScalarEvolution &SE) {
auto *X = SE.getSCEV(getInstructionByName(F, "x"));
auto *Y = SE.getSCEV(getInstructionByName(F, "y"));
auto *Guarded = getInstructionByName(F, "y")->getParent();
ASSERT_TRUE(Guarded);
EXPECT_TRUE(
SE.isBasicBlockEntryGuardedByCond(Guarded, ICmpInst::ICMP_ULT, Y, X));
EXPECT_TRUE(
SE.isBasicBlockEntryGuardedByCond(Guarded, ICmpInst::ICMP_UGT, X, Y));
});
}
} // end namespace llvm