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[SCEV] Return zero from computeConstantDifference(X, X)

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Without this patch computeConstantDifference returns None for cases like
these:

  computeConstantDifference(%x, %x)
  computeConstantDifference({%x,+,16}, {%x,+,16})

Differential Revision: https://reviews.llvm.org/D65474

llvm-svn: 368193
This commit is contained in:
Nikolai Bozhenov 2019-08-07 17:38:38 +00:00
parent 6fbbb7b6b8
commit bb986bef44
3 changed files with 74 additions and 2 deletions
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2
include/llvm/Analysis/ScalarEvolution.h
View File

@ -468,6 +468,8 @@ template <> struct DenseMapInfo<ExitLimitQuery> {
/// can't do much with the SCEV objects directly, they must ask this class
/// for services.
class ScalarEvolution {
friend class ScalarEvolutionsTest;
public:
/// An enum describing the relationship between a SCEV and a loop.
enum LoopDisposition {

4
lib/Analysis/ScalarEvolution.cpp
View File

@ -9833,6 +9833,10 @@ Optional<APInt> ScalarEvolution::computeConstantDifference(const SCEV *More,
// We avoid subtracting expressions here because this function is usually
// fairly deep in the call stack (i.e. is called many times).
// X - X = 0.
if (More == Less)
return APInt(getTypeSizeInBits(More->getType()), 0);
if (isa<SCEVAddRecExpr>(Less) && isa<SCEVAddRecExpr>(More)) {
const auto *LAR = cast<SCEVAddRecExpr>(Less);
const auto *MAR = cast<SCEVAddRecExpr>(More);

70
unittests/Analysis/ScalarEvolutionTest.cpp
View File

@ -26,7 +26,6 @@
#include "gtest/gtest.h"
namespace llvm {
namespace {
// We use this fixture to ensure that we clean up ScalarEvolution before
// deleting the PassManager.
@ -58,6 +57,12 @@ protected:
ScalarEvolution SE = buildSE(*F);
Test(*F, *LI, SE);
}
static Optional<APInt> computeConstantDifference(ScalarEvolution &SE,
const SCEV *LHS,
const SCEV *RHS) {
return SE.computeConstantDifference(LHS, RHS);
}
};
TEST_F(ScalarEvolutionsTest, SCEVUnknownRAUW) {
@ -1678,5 +1683,66 @@ TEST_F(ScalarEvolutionsTest, SCEVExpanderShlNSW) {
"} ");
}
} // end anonymous namespace
TEST_F(ScalarEvolutionsTest, SCEVComputeConstantDifference) {
LLVMContext C;
SMDiagnostic Err;
std::unique_ptr<Module> M = parseAssemblyString(
"define void @foo(i32 %sz, i32 %pp) { "
"entry: "
" %v0 = add i32 %pp, 0 "
" %v3 = add i32 %pp, 3 "
" br label %loop.body "
"loop.body: "
" %iv = phi i32 [ %iv.next, %loop.body ], [ 0, %entry ] "
" %xa = add nsw i32 %iv, %v0 "
" %yy = add nsw i32 %iv, %v3 "
" %xb = sub nsw i32 %yy, 3 "
" %iv.next = add nsw i32 %iv, 1 "
" %cmp = icmp sle i32 %iv.next, %sz "
" br i1 %cmp, label %loop.body, label %exit "
"exit: "
" ret void "
"} ",
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 *ScevV0 = SE.getSCEV(getInstructionByName(F, "v0")); // %pp
auto *ScevV3 = SE.getSCEV(getInstructionByName(F, "v3")); // (3 + %pp)
auto *ScevIV = SE.getSCEV(getInstructionByName(F, "iv")); // {0,+,1}
auto *ScevXA = SE.getSCEV(getInstructionByName(F, "xa")); // {%pp,+,1}
auto *ScevYY = SE.getSCEV(getInstructionByName(F, "yy")); // {(3 + %pp),+,1}
auto *ScevXB = SE.getSCEV(getInstructionByName(F, "xb")); // {%pp,+,1}
auto *ScevIVNext = SE.getSCEV(getInstructionByName(F, "iv.next")); // {1,+,1}
auto diff = [&SE](const SCEV *LHS, const SCEV *RHS) -> Optional<int> {
auto ConstantDiffOrNone = computeConstantDifference(SE, LHS, RHS);
if (!ConstantDiffOrNone)
return None;
auto ExtDiff = ConstantDiffOrNone->getSExtValue();
int Diff = ExtDiff;
assert(Diff == ExtDiff && "Integer overflow");
return Diff;
};
EXPECT_EQ(diff(ScevV3, ScevV0), 3);
EXPECT_EQ(diff(ScevV0, ScevV3), -3);
EXPECT_EQ(diff(ScevV0, ScevV0), 0);
EXPECT_EQ(diff(ScevV3, ScevV3), 0);
EXPECT_EQ(diff(ScevIV, ScevIV), 0);
EXPECT_EQ(diff(ScevXA, ScevXB), 0);
EXPECT_EQ(diff(ScevXA, ScevYY), -3);
EXPECT_EQ(diff(ScevYY, ScevXB), 3);
EXPECT_EQ(diff(ScevIV, ScevIVNext), -1);
EXPECT_EQ(diff(ScevIVNext, ScevIV), 1);
EXPECT_EQ(diff(ScevIVNext, ScevIVNext), 0);
EXPECT_EQ(diff(ScevV0, ScevIV), None);
EXPECT_EQ(diff(ScevIVNext, ScevV3), None);
EXPECT_EQ(diff(ScevYY, ScevV3), None);
});
}
} // end namespace llvm