[PATCH] D140593: In the x86_64 medium code model, emit RIP-relative access to local function instead of position-dependent relocation

[Thomas Köppe via Phabricator via llvm-commits]

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Currently, the medium code model for x86_64 emits position-dependent relocations (R_X86_64_64) for local functions (e.g. https://godbolt.org/z/1W7enxzK6), regardless of PIC or no-PIC mode. (This means generically that code compiled with the medium model cannot be linked into a position-independent executable.)

This patch changes the behaviour to unconditionally emit a RIP-relative access, both in PIC and non-PIC mode. This fixes PIC mode, and is perhaps an improvement in non-PIC mode, too, since it results in a shorter instruction. A 32-bit relocation should suffice since the medium memory model demands that all code fit within 2GiB.


https://reviews.llvm.org/D140593

Files:
  llvm/lib/Target/X86/X86ISelLowering.cpp


Index: llvm/lib/Target/X86/X86ISelLowering.cpp
===================================================================
--- llvm/lib/Target/X86/X86ISelLowering.cpp
+++ llvm/lib/Target/X86/X86ISelLowering.cpp
@@ -20488,6 +20488,10 @@
     return X86ISD::Wrapper;
 
   CodeModel::Model M = getTargetMachine().getCodeModel();
+
+  if (M == CodeModel::Medium && isa_and_nonnull<Function>(GV))
+    return X86ISD::WrapperRIP;
+
   if (Subtarget.isPICStyleRIPRel() &&
       (M == CodeModel::Small || M == CodeModel::Kernel))
     return X86ISD::WrapperRIP;


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