From 5cd6deeae352f15ad916123bdeb54bbeea8ffa06 Mon Sep 17 00:00:00 2001 From: Chen Li Date: Wed, 23 Sep 2015 17:58:44 +0000 Subject: [Bug 24848] Use range metadata to constant fold comparisons with constant values Summary: This is the first part of fixing bug 24848 https://llvm.org/bugs/show_bug.cgi?id=24848. When range metadata is provided, it should be used to constant fold comparisons with constant values. Reviewers: sanjoy, hfinkel Subscribers: llvm-commits Differential Revision: http://reviews.llvm.org/D12988 llvm-svn: 248402 --- llvm/lib/Analysis/InstructionSimplify.cpp | 34 +++++++++++++++++++++++++++++-- 1 file changed, 32 insertions(+), 2 deletions(-) (limited to 'llvm/lib/Analysis') diff --git a/llvm/lib/Analysis/InstructionSimplify.cpp b/llvm/lib/Analysis/InstructionSimplify.cpp index b6d4c02a9eb..7f27d8882e7 100644 --- a/llvm/lib/Analysis/InstructionSimplify.cpp +++ b/llvm/lib/Analysis/InstructionSimplify.cpp @@ -2128,6 +2128,29 @@ static Constant *computePointerICmp(const DataLayout &DL, return nullptr; } +static ConstantRange GetConstantRangeFromMetadata(MDNode *Ranges, uint32_t BitWidth) { + const unsigned NumRanges = Ranges->getNumOperands() / 2; + assert(NumRanges >= 1); + + ConstantRange CR(BitWidth, false); + for (unsigned i = 0; i < NumRanges; ++i) { + auto *Low = + mdconst::extract(Ranges->getOperand(2 * i + 0)); + auto *High = + mdconst::extract(Ranges->getOperand(2 * i + 1)); + + // Union will merge two ranges to one and potentially introduce a range + // not covered by the original two ranges. For example, [1, 5) and [8, 10) + // will become [1, 10). In this case, we can not fold comparison between + // constant 6 and a value of the above ranges. In practice, most values + // have only one range, so it might not be worth handling this by + // introducing additional complexity. + CR = CR.unionWith(ConstantRange(Low->getValue(), High->getValue())); + } + + return CR; +} + /// SimplifyICmpInst - Given operands for an ICmpInst, see if we can /// fold the result. If not, this returns null. static Value *SimplifyICmpInst(unsigned Predicate, Value *LHS, Value *RHS, @@ -2364,8 +2387,15 @@ static Value *SimplifyICmpInst(unsigned Predicate, Value *LHS, Value *RHS, // 'add nuw x, CI2' produces [CI2, UINT_MAX]. Lower = CI2->getValue(); } - if (Lower != Upper) { - ConstantRange LHS_CR = ConstantRange(Lower, Upper); + + ConstantRange LHS_CR = Lower != Upper ? ConstantRange(Lower, Upper) + : ConstantRange(Width, true); + + if (auto *I = dyn_cast(LHS)) + if (auto *Ranges = I->getMetadata(LLVMContext::MD_range)) + LHS_CR = LHS_CR.intersectWith(GetConstantRangeFromMetadata(Ranges, Width)); + + if (!LHS_CR.isFullSet()) { if (RHS_CR.contains(LHS_CR)) return ConstantInt::getTrue(RHS->getContext()); if (RHS_CR.inverse().contains(LHS_CR)) -- cgit v1.2.3