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7157a84082
Summary: The value operand in DW_OP_plus_uconst/DW_OP_constu value can be large (it uses uint64_t as representation internally in LLVM). This means that in the uint64_t to int conversions, previously done by DwarfExpression::addMachineRegExpression, could lose information. Also, the negation done in "-Offset" was undefined behavior in case Offset was exactly INT_MIN. To avoid the above problems, we now avoid transformation like [Reg, DW_OP_plus_uconst, Offset] --> [DW_OP_breg, Offset] and [Reg, DW_OP_constu, Offset, DW_OP_plus] --> [DW_OP_breg, Offset] when Offset > INT_MAX. And we avoid to transform [Reg, DW_OP_constu, Offset, DW_OP_minus] --> [DW_OP_breg,-Offset] when Offset > INT_MAX+1. The patch also adjusts DwarfCompileUnit::constructVariableDIEImpl to make sure that "DW_OP_constu, Offset, DW_OP_minus" is used instead of "DW_OP_plus_uconst, Offset" when creating DIExpressions with negative frame index offsets. Notice that this might just be the tip of the iceberg. There are lots of fishy handling related to these constants. I think both DIExpression::appendOffset and DIExpression::extractIfOffset may trigger undefined behavior for certain values. Reviewers: sdesmalen, rnk, JDevlieghere Reviewed By: JDevlieghere Subscribers: jholewinski, aprantl, hiraditya, ychen, uabelho, llvm-commits Tags: #debug-info, #llvm Differential Revision: https://reviews.llvm.org/D67263 llvm-svn: 371304