diff options
Diffstat (limited to 'llvm/lib')
| -rw-r--r-- | llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp | 34 |
1 files changed, 19 insertions, 15 deletions
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp b/llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp index 9d96ddc4040..8ab4aeb38be 100644 --- a/llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp +++ b/llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp @@ -61,16 +61,10 @@ reassociateShiftAmtsOfTwoSameDirectionShifts(BinaryOperator *Sh0, if (ShiftOpcode != Sh1->getOpcode()) return nullptr; - // Did we match a pattern with truncation ? - if (Trunc) { - // For right-shifts we can't do any such simplifications. Leave as-is. - if (ShiftOpcode != Instruction::BinaryOps::Shl) - return nullptr; // FIXME: still could perform constant-folding. - // If we saw truncation, we'll need to produce extra instruction, - // and for that one of the operands of the shift must be one-use. - if (!match(Sh0, m_c_BinOp(m_OneUse(m_Value()), m_Value()))) - return nullptr; - } + // If we saw truncation, we'll need to produce extra instruction, + // and for that one of the operands of the shift must be one-use. + if (Trunc && !match(Sh0, m_c_BinOp(m_OneUse(m_Value()), m_Value()))) + return nullptr; // Can we fold (ShAmt0+ShAmt1) ? auto *NewShAmt = dyn_cast_or_null<Constant>( @@ -78,13 +72,23 @@ reassociateShiftAmtsOfTwoSameDirectionShifts(BinaryOperator *Sh0, SQ.getWithInstruction(Sh0))); if (!NewShAmt) return nullptr; // Did not simplify. - // Is the new shift amount smaller than the bit width of inner shift? - if (!match(NewShAmt, m_SpecificInt_ICMP( - ICmpInst::Predicate::ICMP_ULT, - APInt(NewShAmt->getType()->getScalarSizeInBits(), - X->getType()->getScalarSizeInBits())))) + unsigned NewShAmtBitWidth = NewShAmt->getType()->getScalarSizeInBits(); + unsigned XBitWidth = X->getType()->getScalarSizeInBits(); + // Is the new shift amount smaller than the bit width of inner/new shift? + if (!match(NewShAmt, m_SpecificInt_ICMP(ICmpInst::Predicate::ICMP_ULT, + APInt(NewShAmtBitWidth, XBitWidth)))) return nullptr; // FIXME: could perform constant-folding. + // If there was a truncation, and we have a right-shift, we can only fold if + // we are left with the original sign bit. + // FIXME: zero shift amount is also legal here, but we can't *easily* check + // more than one predicate so it's not really worth it. + if (Trunc && ShiftOpcode != Instruction::BinaryOps::Shl && + !match(NewShAmt, + m_SpecificInt_ICMP(ICmpInst::Predicate::ICMP_EQ, + APInt(NewShAmtBitWidth, XBitWidth - 1)))) + return nullptr; + // All good, we can do this fold. NewShAmt = ConstantExpr::getZExtOrBitCast(NewShAmt, X->getType()); |
