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[SCEV] Properly handle the case of a non-constant start with a zero accum in ScalarEvolution::createAddRecFromPHIWithCastsImpl

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Summary:
 This patch fixes an error in the patch to ScalarEvolution::createAddRecFromPHIWithCastsImpl
made in D37265. In that patch we handle the cases where the either the start or accum values can be
zero after truncation. But, we assume that the start value must be a constant if the accum is
zero. This is clearly an erroneous assumption. This change removes that assumption.

Reviewers: sanjoy, dorit, mkazantsev

Reviewed By: sanjoy

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D38814

llvm-svn: 315491
This commit is contained in:
Daniel Neilson 2017-10-11 19:05:14 +00:00
parent 1112a82774
commit 6a302cca5a
2 changed files with 58 additions and 3 deletions
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3
lib/Analysis/ScalarEvolution.cpp
View File

@ -4523,8 +4523,7 @@ ScalarEvolution::createAddRecFromPHIWithCastsImpl(const SCEVUnknown *SymbolicPHI
: SCEVWrapPredicate::IncrementNUSW;
const SCEVPredicate *AddRecPred = getWrapPredicate(AR, AddedFlags);
Predicates.push_back(AddRecPred);
} else
assert(isa<SCEVConstant>(PHISCEV) && "Expected constant SCEV");
}
// Create the Equal Predicates P2,P3:

58
unittests/Analysis/ScalarEvolutionTest.cpp
View File

@ -1009,6 +1009,63 @@ TEST_F(ScalarEvolutionsTest, SCEVAddRecFromPHIwithLargeConstants) {
auto Result = SE.createAddRecFromPHIWithCasts(cast<SCEVUnknown>(Expr));
}
TEST_F(ScalarEvolutionsTest, SCEVAddRecFromPHIwithLargeConstantAccum) {
// Make sure that SCEV does not blow up when constructing an AddRec
// with predicates for a phi with the update pattern:
// (SExt/ZExt ix (Trunc iy (%SymbolicPHI) to ix) to iy) + InvariantAccum
// when the InvariantAccum is a constant that is too large to fit in an
// ix but are zero when truncated to ix, and the initial value of the
// phi is not a constant.
Type *Int32Ty = Type::getInt32Ty(Context);
SmallVector<Type *, 1> Types;
Types.push_back(Int32Ty);
FunctionType *FTy = FunctionType::get(Type::getVoidTy(Context), Types, false);
Function *F = cast<Function>(M.getOrInsertFunction("addrecphitest", FTy));
/*
Create IR:
define @addrecphitest(i32)
entry:
br label %loop
loop:
%1 = phi i32 [%0, %entry], [%4, %loop]
%2 = shl i32 %1, 16
%3 = ashr exact i32 %2, 16
%4 = add i32 %3, -2147483648
br i1 undef, label %exit, label %loop
exit:
ret void
*/
BasicBlock *EntryBB = BasicBlock::Create(Context, "entry", F);
BasicBlock *LoopBB = BasicBlock::Create(Context, "loop", F);
BasicBlock *ExitBB = BasicBlock::Create(Context, "exit", F);
// entry:
BranchInst::Create(LoopBB, EntryBB);
// loop:
auto *MinInt32 = ConstantInt::get(Context, APInt(32, 0x80000000U, true));
auto *Int32_16 = ConstantInt::get(Context, APInt(32, 16));
auto *Br = BranchInst::Create(
LoopBB, ExitBB, UndefValue::get(Type::getInt1Ty(Context)), LoopBB);
auto *Phi = PHINode::Create(Int32Ty, 2, "", Br);
auto *Shl = BinaryOperator::CreateShl(Phi, Int32_16, "", Br);
auto *AShr = BinaryOperator::CreateExactAShr(Shl, Int32_16, "", Br);
auto *Add = BinaryOperator::CreateAdd(AShr, MinInt32, "", Br);
auto *Arg = &*(F->arg_begin());
Phi->addIncoming(Arg, EntryBB);
Phi->addIncoming(Add, LoopBB);
// exit:
ReturnInst::Create(Context, nullptr, ExitBB);
// Make sure that SCEV doesn't blow up
ScalarEvolution SE = buildSE(*F);
SCEVUnionPredicate Preds;
const SCEV *Expr = SE.getSCEV(Phi);
EXPECT_NE(nullptr, Expr);
EXPECT_TRUE(isa<SCEVUnknown>(Expr));
auto Result = SE.createAddRecFromPHIWithCasts(cast<SCEVUnknown>(Expr));
}
TEST_F(ScalarEvolutionsTest, SCEVFoldSumOfTruncs) {
// Verify that the following SCEV gets folded to a zero:
// (-1 * (trunc i64 (-1 * %0) to i32)) + (-1 * (trunc i64 %0 to i32)
@ -1035,7 +1092,6 @@ TEST_F(ScalarEvolutionsTest, SCEVFoldSumOfTruncs) {
const auto *B = SE.getNegativeSCEV(B0);
const auto *Expr = SE.getAddExpr(A, B);
dbgs() << "DDN\nExpr: " << *Expr << "\n";
// Verify that the SCEV was folded to 0
const auto *ZeroConst = SE.getConstant(Int32Ty, 0);
EXPECT_EQ(Expr, ZeroConst);