From 0f46e31cfbf415fcd3d3ce121bef94e92c6ccfc8 Mon Sep 17 00:00:00 2001 From: Nikita Popov Date: Wed, 20 Mar 2024 10:59:45 +0100 Subject: [IR] Change representation of getelementptr inrange (#84341) As part of the migration to ptradd (https://discourse.llvm.org/t/rfc-replacing-getelementptr-with-ptradd/68699), we need to change the representation of the `inrange` attribute, which is used for vtable splitting. Currently, inrange is specified as follows: ``` getelementptr inbounds ({ [4 x ptr], [4 x ptr] }, ptr @vt, i64 0, inrange i32 1, i64 2) ``` The `inrange` is placed on a GEP index, and all accesses must be "in range" of that index. The new representation is as follows: ``` getelementptr inbounds inrange(-16, 16) ({ [4 x ptr], [4 x ptr] }, ptr @vt, i64 0, i32 1, i64 2) ``` This specifies which offsets are "in range" of the GEP result. The new representation will continue working when canonicalizing to ptradd representation: ``` getelementptr inbounds inrange(-16, 16) (i8, ptr @vt, i64 48) ``` The inrange offsets are relative to the return value of the GEP. An alternative design could make them relative to the source pointer instead. The result-relative format was chosen on the off-chance that we want to extend support to non-constant GEPs in the future, in which case this variant is more expressive. This implementation "upgrades" the old inrange representation in bitcode by simply dropping it. This is a very niche feature, and I don't think trying to upgrade it is worthwhile. Let me know if you disagree. --- llvm/lib/Bitcode/Writer/BitcodeWriter.cpp | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-) (limited to 'llvm/lib/Bitcode/Writer/BitcodeWriter.cpp') diff --git a/llvm/lib/Bitcode/Writer/BitcodeWriter.cpp b/llvm/lib/Bitcode/Writer/BitcodeWriter.cpp index fd211f7..a1ee029 100644 --- a/llvm/lib/Bitcode/Writer/BitcodeWriter.cpp +++ b/llvm/lib/Bitcode/Writer/BitcodeWriter.cpp @@ -2751,9 +2751,10 @@ void ModuleBitcodeWriter::writeConstants(unsigned FirstVal, unsigned LastVal, Code = bitc::CST_CODE_CE_GEP; const auto *GO = cast(C); Record.push_back(VE.getTypeID(GO->getSourceElementType())); - if (std::optional Idx = GO->getInRangeIndex()) { - Code = bitc::CST_CODE_CE_GEP_WITH_INRANGE_INDEX; - Record.push_back((*Idx << 1) | GO->isInBounds()); + if (std::optional Range = GO->getInRange()) { + Code = bitc::CST_CODE_CE_GEP_WITH_INRANGE; + Record.push_back(GO->isInBounds()); + emitConstantRange(Record, *Range); } else if (GO->isInBounds()) Code = bitc::CST_CODE_CE_INBOUNDS_GEP; for (unsigned i = 0, e = CE->getNumOperands(); i != e; ++i) { -- cgit v1.1