[PATCH] D88087: [SCEV] Limited support for unsigned preds in isImpliedViaOperations
Max Kazantsev via Phabricator via llvm-commits
llvm-commits at lists.llvm.org
Thu Oct 1 20:40:52 PDT 2020
This revision was not accepted when it landed; it landed in state "Needs Review".
This revision was automatically updated to reflect the committed changes.
Closed by commit rGb8ac19cf1cca: [SCEV] Limited support for unsigned preds in isImpliedViaOperations (authored by mkazantsev).
Changed prior to commit:
https://reviews.llvm.org/D88087?vs=295486&id=295723#toc
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D88087/new/
https://reviews.llvm.org/D88087
Files:
llvm/lib/Analysis/ScalarEvolution.cpp
llvm/unittests/Analysis/ScalarEvolutionTest.cpp
Index: llvm/unittests/Analysis/ScalarEvolutionTest.cpp
===================================================================
--- llvm/unittests/Analysis/ScalarEvolutionTest.cpp
+++ llvm/unittests/Analysis/ScalarEvolutionTest.cpp
@@ -1283,4 +1283,37 @@
});
}
+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
Index: llvm/lib/Analysis/ScalarEvolution.cpp
===================================================================
--- llvm/lib/Analysis/ScalarEvolution.cpp
+++ llvm/lib/Analysis/ScalarEvolution.cpp
@@ -10236,13 +10236,31 @@
// 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;
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