[PATCH] D47211: [X86] Implement more of x86-64 large and medium PIC code models
Reid Kleckner via Phabricator via llvm-commits
llvm-commits at lists.llvm.org
Tue May 22 11:29:05 PDT 2018
rnk created this revision.
rnk added reviewers: chandlerc, echristo.
Herald added a subscriber: hiraditya.
The large code model allows code and data segments to exceed 2GB, which
means that some symbol references may require a displacement that cannot
be encoded as a displacement from RIP. The large PIC model even relaxes
the assumption that the GOT itself is within 2GB of all code. Therefore,
we need a special code sequence to materialize it:
.LtmpN:
leaq .LtmpN(%rip), %rbx
movabsq $_GLOBAL_OFFSET_TABLE_-.LtmpN, %rax # Scratch
addq %rax, %rbx # GOT base reg
>From that, non-local references go through the GOT base register instead
of being PC-relative loads. Local references typically use GOTOFF
symbols, like this:
movq extern_gv at GOT(%rbx), %rax
movq local_gv at GOTOFF(%rbx), %rax
All calls end up being indirect:
movabsq $local_fn at GOTOFF, %rax
addq %rbx, %rax
callq *%rax
The medium code model retains the assumption that the code segment is
less than 2GB, so calls are once again direct, and the RIP-relative
loads can be used to access the GOT. Materializing the GOT is easy:
leaq _GLOBAL_OFFSET_TABLE_(%rip), %rbx # GOT base reg
DSO local data accesses will use it:
movq local_gv at GOTOFF(%rbx), %rax
Non-local data accesses will use RIP-relative addressing, which means we
may not always need to materialize the GOT base:
movq extern_gv at GOTPCREL(%rip), %rax
Direct calls are basically the same as they are in the small code model:
They use direct, PC-relative addressing, and the PLT is used for calls
to non-local functions.
This patch adds reasonably comprehensive testing of LEA, but there are
lots of interesting folding opportunities that are unimplemented.
https://reviews.llvm.org/D47211
Files:
llvm/lib/Target/X86/X86ISelDAGToDAG.cpp
llvm/lib/Target/X86/X86InstrCompiler.td
llvm/lib/Target/X86/X86InstrInfo.cpp
llvm/lib/Target/X86/X86MCInstLower.cpp
llvm/lib/Target/X86/X86Subtarget.cpp
llvm/lib/Target/X86/X86TargetMachine.cpp
llvm/test/CodeGen/X86/cleanuppad-large-codemodel.ll
llvm/test/CodeGen/X86/code-model.ll
llvm/test/CodeGen/X86/fast-isel-call-cleanup.ll
llvm/test/CodeGen/X86/fast-isel-constpool.ll
llvm/test/CodeGen/X86/hipe-cc64.ll
llvm/utils/UpdateTestChecks/asm.py
llvm/utils/update_llc_test_checks.py
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