From: Reid Kleckner <rnk@google.com>
Date: Fri, 24 May 2019 01:27:20 +0000 (+0000)
Subject: [AArch64] Preserve X8 for thunks ending in variadic musttail calls
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=85ea819c593705b0694f8749eba9f41e7866cca5;p=llvm

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

Summary:
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

Reviewers: mgrang, efriedma

Subscribers: javed.absar, kristof.beyls, hiraditya, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D62344

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@361585 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/lib/Target/AArch64/AArch64ISelLowering.cpp b/lib/Target/AArch64/AArch64ISelLowering.cpp
index 4b027e93633..ac656959bcb 100644
--- a/lib/Target/AArch64/AArch64ISelLowering.cpp
+++ b/lib/Target/AArch64/AArch64ISelLowering.cpp
@@ -3207,6 +3207,12 @@ SDValue AArch64TargetLowering::LowerFormalArguments(
                                        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));
+      }
     }
   }
 
diff --git a/test/CodeGen/AArch64/vararg-tallcall.ll b/test/CodeGen/AArch64/vararg-tallcall.ll
index 28182226803..56c56213af3 100644
--- a/test/CodeGen/AArch64/vararg-tallcall.ll
+++ b/test/CodeGen/AArch64/vararg-tallcall.ll
@@ -28,7 +28,7 @@ entry:
 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