[llvm-branch-commits] [llvm] release/19.x: [PPC][AIX] Save/restore r31 when using base pointer (#100182) (PR #103301)

[Tobias Hieta via llvm-branch-commits]

https://github.com/tru updated https://github.com/llvm/llvm-project/pull/103301

>From 9c3d4f344685f7695bb8e05677d8684fa3aa1f72 Mon Sep 17 00:00:00 2001
From: Zaara Syeda <syzaara at ca.ibm.com>
Date: Wed, 7 Aug 2024 09:59:45 -0400
Subject: [PATCH] [PPC][AIX] Save/restore r31 when using base pointer (#100182)

When the base pointer r30 is used to hold the stack pointer, r30 is
spilled in the prologue. On AIX registers are saved from highest to
lowest, so r31 also needs to be saved.

Fixes https://github.com/llvm/llvm-project/issues/96411

(cherry picked from commit d07f106e512c08455b76cc1889ee48318e73c810)
---
 llvm/lib/Target/PowerPC/PPCFrameLowering.cpp  | 14 ++++++++++++--
 llvm/test/CodeGen/PowerPC/aix-base-pointer.ll |  5 +++++
 2 files changed, 17 insertions(+), 2 deletions(-)

diff --git a/llvm/lib/Target/PowerPC/PPCFrameLowering.cpp b/llvm/lib/Target/PowerPC/PPCFrameLowering.cpp
index 1963582ce68631..a57ed33bda9c77 100644
--- a/llvm/lib/Target/PowerPC/PPCFrameLowering.cpp
+++ b/llvm/lib/Target/PowerPC/PPCFrameLowering.cpp
@@ -1007,7 +1007,7 @@ void PPCFrameLowering::emitPrologue(MachineFunction &MF,
         // R0 cannot be used as a base register, but it can be used as an
         // index in a store-indexed.
         int LastOffset = 0;
-        if (HasFP)  {
+        if (HasFP) {
           // R0 += (FPOffset-LastOffset).
           // Need addic, since addi treats R0 as 0.
           BuildMI(MBB, MBBI, dl, TII.get(PPC::ADDIC), ScratchReg)
@@ -2025,8 +2025,18 @@ void PPCFrameLowering::determineCalleeSaves(MachineFunction &MF,
   // code. Same goes for the base pointer and the PIC base register.
   if (needsFP(MF))
     SavedRegs.reset(isPPC64 ? PPC::X31 : PPC::R31);
-  if (RegInfo->hasBasePointer(MF))
+  if (RegInfo->hasBasePointer(MF)) {
     SavedRegs.reset(RegInfo->getBaseRegister(MF));
+    // On AIX, when BaseRegister(R30) is used, need to spill r31 too to match
+    // AIX trackback table requirement.
+    if (!needsFP(MF) && !SavedRegs.test(isPPC64 ? PPC::X31 : PPC::R31) &&
+        Subtarget.isAIXABI()) {
+      assert(
+          (RegInfo->getBaseRegister(MF) == (isPPC64 ? PPC::X30 : PPC::R30)) &&
+          "Invalid base register on AIX!");
+      SavedRegs.set(isPPC64 ? PPC::X31 : PPC::R31);
+    }
+  }
   if (FI->usesPICBase())
     SavedRegs.reset(PPC::R30);
 
diff --git a/llvm/test/CodeGen/PowerPC/aix-base-pointer.ll b/llvm/test/CodeGen/PowerPC/aix-base-pointer.ll
index ab222d770360ce..5e66e5ec276389 100644
--- a/llvm/test/CodeGen/PowerPC/aix-base-pointer.ll
+++ b/llvm/test/CodeGen/PowerPC/aix-base-pointer.ll
@@ -6,6 +6,7 @@
 
 ; Use an overaligned buffer to force base-pointer usage. Test verifies:
 ; - base pointer register (r30) is saved/defined/restored.
+; - frame pointer register (r31) is saved/defined/restored.
 ; - stack frame is allocated with correct alignment.
 ; - Address of %AlignedBuffer is calculated based off offset from the stack
 ;   pointer.
@@ -25,7 +26,9 @@ declare void @callee(ptr)
 ; 32BIT:         subfic 0, 0, -224
 ; 32BIT:         stwux 1, 1, 0
 ; 32BIT:         addi 3, 1, 64
+; 32BIT:         stw 31, -12(30)
 ; 32BIT:         bl .callee
+; 32BIT:         lwz 31, -12(30)
 ; 32BIT:         mr 1, 30
 ; 32BIT:         lwz 30, -16(1)
 
@@ -36,6 +39,8 @@ declare void @callee(ptr)
 ; 64BIT:         subfic 0, 0, -288
 ; 64BIT:         stdux 1, 1, 0
 ; 64BIT:         addi 3, 1, 128
+; 64BIT:         std 31, -16(30)
 ; 64BIT:         bl .callee
+; 64BIT:         ld 31, -16(30)
 ; 64BIT:         mr 1, 30
 ; 64BIT:         ld 30, -24(1)