From 73f8b255b66fb1eca6da49076b3301bf2dcb23ed Mon Sep 17 00:00:00 2001 From: Hiroshi Inoue Date: Fri, 3 Aug 2018 05:39:48 +0000 Subject: [InstSimplify] fold extracting from std::pair (2/2) This is the second patch of the series which intends to enable jump threading for an inlined method whose return type is std::pair or std::pair. The first patch is https://reviews.llvm.org/rL338485. This patch handles code sequences that merges two values using `shl` and `or`, then extracts one value using `and`. Differential Revision: https://reviews.llvm.org/D49981 llvm-svn: 338817 --- llvm/lib/Analysis/InstructionSimplify.cpp | 34 +++++++++++++++++++++++++++++++ 1 file changed, 34 insertions(+) (limited to 'llvm/lib/Analysis') diff --git a/llvm/lib/Analysis/InstructionSimplify.cpp b/llvm/lib/Analysis/InstructionSimplify.cpp index ffdbfc45c84..494ca656dba 100644 --- a/llvm/lib/Analysis/InstructionSimplify.cpp +++ b/llvm/lib/Analysis/InstructionSimplify.cpp @@ -1863,6 +1863,40 @@ static Value *SimplifyAndInst(Value *Op0, Value *Op1, const SimplifyQuery &Q, MaxRecurse)) return V; + // Assuming the effective width of Y is not larger than A, i.e. all bits + // from X and Y are disjoint in (X << A) | Y, + // if the mask of this AND op covers all bits of X or Y, while it covers + // no bits from the other, we can bypass this AND op. E.g., + // ((X << A) | Y) & Mask -> Y, + // if Mask = ((1 << effective_width_of(Y)) - 1) + // ((X << A) | Y) & Mask -> X << A, + // if Mask = ((1 << effective_width_of(X)) - 1) << A + // SimplifyDemandedBits in InstCombine can optimize the general case. + // This pattern aims to help other passes for a common case. + Value *Y, *XShifted; + if (match(Op1, m_APInt(Mask)) && + match(Op0, m_c_Or(m_CombineAnd(m_NUWShl(m_Value(X), m_APInt(ShAmt)), + m_Value(XShifted)), + m_Value(Y)))) { + const unsigned ShftCnt = ShAmt->getZExtValue(); + const KnownBits YKnown = computeKnownBits(Y, Q.DL, 0, Q.AC, Q.CxtI, Q.DT); + const unsigned Width = Op0->getType()->getScalarSizeInBits(); + const unsigned EffWidthY = Width - YKnown.countMinLeadingZeros(); + if (EffWidthY <= ShftCnt) { + const KnownBits XKnown = computeKnownBits(X, Q.DL, 0, Q.AC, Q.CxtI, + Q.DT); + const unsigned EffWidthX = Width - XKnown.countMinLeadingZeros(); + const APInt EffBitsY = APInt::getLowBitsSet(Width, EffWidthY); + const APInt EffBitsX = APInt::getLowBitsSet(Width, EffWidthX) << ShftCnt; + // If the mask is extracting all bits from X or Y as is, we can skip + // this AND op. + if (EffBitsY.isSubsetOf(*Mask) && !EffBitsX.intersects(*Mask)) + return Y; + if (EffBitsX.isSubsetOf(*Mask) && !EffBitsY.intersects(*Mask)) + return XShifted; + } + } + return nullptr; } -- cgit v1.2.3