[PATCH] D155600: [AIX][TLS] Produce a faster local-exec access sequence with -maix-small-local-exec-tls (And optimize when load/store offsets are 0)

[Hubert Tong via Phabricator via llvm-commits]

hubert.reinterpretcast added inline comments.


================
Comment at: llvm/lib/Target/PowerPC/PPCAsmPrinter.cpp:1584
+  // Handle small-local-exec-tls accesses only for the local-exec TLS model,
+  // which is represented by the MO_TREL_FLAG target flag.
+  if (!(MO.getTargetFlags() & PPCII::MO_TPREL_FLAG))
----------------
Typo?


================
Comment at: llvm/lib/Target/PowerPC/PPCISelLowering.cpp:155
+// size of 32KB or under.
+static uint64_t AIXTLSUpperDisplacement = 32760;
+
----------------
Should be `constexpr`.


================
Comment at: llvm/lib/Target/PowerPC/PPCISelLowering.cpp:3356
+      // the offset from the TLS base is encoded as an immediate operand.
+      // This is available on 64-bit mode only.
+      //
----------------
The last sentence is redundant with statements made on the 32-bit path.


================
Comment at: llvm/lib/Target/PowerPC/PPCISelLowering.cpp:3364
+      uint64_t GVTypeSize =
+          GV->getParent()->getDataLayout().getTypeAllocSize(GV->getValueType());
+      if (HasAIXSmallLocalExecTLS &&
----------------
ICE/assert:
```
clang: /terrannew/hstong/.Lpcoral03/llvmbld/dev/llvm-project/llvm/include/llvm/IR/DataLayout.h:669: TypeSize llvm::DataLayout::getTypeSizeInBits(Type *) const: Assertion `Ty->isSized() && "Cannot getTypeInfo() on a type that is unsized!"' failed.
```
with
```
clang --target=powerpc64-ibm-aix -c -o /dev/null -xc++ -<<<$'extern __thread struct X x [[gnu::tls_model("local-exec")]];\nvoid *f() { return &x; }'
```

A similar case with an array of unknown bound does not assert; however, it does generate the small TLS access pattern despite the size being unknown (and potentially huge).


================
Comment at: llvm/lib/Target/PowerPC/PPCISelLowering.cpp:3378-3379
+
+      // The faster access sequence for local-exec controlled by
+      // -maix-small-local-exec-tls is not available on 32-bit mode.
+      if (HasAIXSmallLocalExecTLS)
----------------
The comment should be clear that there is a 32-bit version that is merely omitted by the implementation here.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D155600/new/

https://reviews.llvm.org/D155600