[PATCH] D62344: [AArch64] Preserve X8 for thunks ending in variadic musttail calls

[Reid Kleckner via Phabricator via llvm-commits]

rnk created this revision.
rnk added reviewers: mgrang, efriedma.
Herald added subscribers: hiraditya, kristof.beyls, javed.absar.
Herald added a project: LLVM.

On Windows, X8 may be used to pass in the address of an aggregate that
is returned indirectly. Therefore, it should be forwarded to variadic
musttail calls and preserved in thunks.

Fixes PR41997


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D62344

Files:
  llvm/lib/Target/AArch64/AArch64ISelLowering.cpp
  llvm/test/CodeGen/AArch64/vararg-tallcall.ll


Index: llvm/test/CodeGen/AArch64/vararg-tallcall.ll
===================================================================
--- llvm/test/CodeGen/AArch64/vararg-tallcall.ll
+++ llvm/test/CodeGen/AArch64/vararg-tallcall.ll
@@ -28,7 +28,7 @@
 attributes #1 = { noinline optnone "thunk" }
 
 ; CHECK: mov     v16.16b, v0.16b
-; CHECK: ldr     x8, [x0]
-; CHECK: ldr     x8, [x8]
+; CHECK: ldr     x9, [x0]
+; CHECK: ldr     x9, [x9]
 ; CHECK: mov     v0.16b, v16.16b
-; CHECK: br      x8
+; CHECK: br      x9
Index: llvm/lib/Target/AArch64/AArch64ISelLowering.cpp
===================================================================
--- llvm/lib/Target/AArch64/AArch64ISelLowering.cpp
+++ llvm/lib/Target/AArch64/AArch64ISelLowering.cpp
@@ -3207,6 +3207,12 @@
                                        FuncInfo->getForwardedMustTailRegParms();
       CCInfo.analyzeMustTailForwardedRegisters(Forwards, RegParmTypes,
                                                CC_AArch64_AAPCS);
+
+      // Conservatively forward X8, since it might be used for aggregate return.
+      if (!CCInfo.isAllocated(AArch64::X8)) {
+        unsigned X8VReg = MF.addLiveIn(AArch64::X8, &AArch64::GPR64RegClass);
+        Forwards.push_back(ForwardedRegister(X8VReg, AArch64::X8, MVT::i64));
+      }
     }
   }
 


-------------- next part --------------
A non-text attachment was scrubbed...
Name: D62344.201059.patch
Type: text/x-patch
Size: 1285 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20190523/36861880/attachment.bin>