This patch fixes several routines which deal with negation but failed to use the proper floating point negation formula, f(x) = -0.0 - x, for vectors. I simply factored out the logic to get the properly-signed "zero" value and extended it to get the correct floating-point vector. In most cases, these local logic errors were harmless because callers operated exclusively on scalar integers, but in four cases there look to be potential problems or missed optimizations. This patch fixes the dead m_Neg matcher that patch 3 commented out. at lib/Transforms/Scalar/InstructionCombining.cpp:6788: NegVal = InsertNewInstBefore( BinaryOperator::createNeg(SubOp->getOperand(1), "tmp"), SI); This can pass vectors to createNeg and looks like it would previous miscompile code by inserting a sub <+0.0, +0.0, etc.>, %x as it simplifies an _expression_. This patch should fix this case. at lib/Target/CBackend/CBackend.cpp:2129 This is now http://llvm.org/PR1126. at lib/Transforms/Scalar/InstructionCombining.cpp:325: Please review this call site in getComplexity. It is clearly reachable with FP vector operands, and isNeg will now return true for vector negation, which is not a single machine instruction as fneg or integer negation are. Therefore, existing behavior might be preferable? If so, exclude vectors: - if (BinaryOperator::isNeg(V) || BinaryOperator::isNot(V)) + if ((!isa<PackedType>(V->getType()) && BinaryOperator::isNeg(V)) || + BinaryOperator::isNot(V)) at lib/Transforms/Scalar/InstructionCombining.cpp:473: static inline Value *dyn_castNegVal(Value *V) { if (BinaryOperator::isNeg(V)) return BinaryOperator::getNegArgument(V); This could clearly be invoked with FP vector operands. With this patch, the following transformations would be extended to FP vectors: -A + B --> B - A A + -B --> A - B A - (-B) --> A + B -X * -Y --> X * Y These would already have applied to scalar FP operations, so I have to assume that they're IEEE-approved. Just one more! |
pr970-4.patch
Description: Binary data
_______________________________________________ llvm-commits mailing list llvm-commits@cs.uiuc.edu http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits
