[AIX] Implement function descriptor on SDAG
Summary:
(1) Function descriptor on AIX
On AIX, a called routine may have 2 distinct symbols associated with it:
* A function descriptor (Name)
* A function entry point (.Name)
The descriptor structure on AIX is the same as those in the ELF V1 ABI:
* The address of the entry point of the function.
* The TOC base address for the function.
* The environment pointer.
The descriptor symbol uses the same name as the source level function in C.
The function entry point is analogous to the symbol we would generate for a
function in a non-descriptor-based ABI, except that it is renamed by
prepending a ".".
Which symbol gets referenced depends on the context:
* Taking the address of the function references the descriptor symbol.
* Calling the function references the entry point symbol.
(2) Speaking of implementation on AIX, for direct function call target, we
create proper MCSymbol SDNode(e.g . ".foo") while constructing SDAG to
replace original TargetGlobalAddress SDNode. Then down the path, we can
take advantage of this MCSymbol.
Patch by: Xiangling_L
Reviewed by: sfertile, hubert.reinterpretcast, jasonliu, syzaara
Differential Revision: https://reviews.llvm.org/D62532
llvm-svn: 362735
diff --git a/llvm/lib/Target/PowerPC/PPCFastISel.cpp b/llvm/lib/Target/PowerPC/PPCFastISel.cpp
index e22e682..264d6b5 100644
--- a/llvm/lib/Target/PowerPC/PPCFastISel.cpp
+++ b/llvm/lib/Target/PowerPC/PPCFastISel.cpp
@@ -1964,6 +1964,13 @@
case Instruction::Sub:
return SelectBinaryIntOp(I, ISD::SUB);
case Instruction::Call:
+ // On AIX, call lowering uses the DAG-ISEL path currently so that the
+ // callee of the direct function call instruction will be mapped to the
+ // symbol for the function's entry point, which is distinct from the
+ // function descriptor symbol. The latter is the symbol whose XCOFF symbol
+ // name is the C-linkage name of the source level function.
+ if (TM.getTargetTriple().isOSAIX())
+ break;
return selectCall(I);
case Instruction::Ret:
return SelectRet(I);