release/19.x: [PPC][AIX] Save/restore r31 when using base pointer (#100182)

[llvmbot]

Backport d07f106

Requested by: @syzaara

[llvmbot]

@mandlebug What do you think about merging this PR to the release branch?

[llvmbot]

@llvm/pr-subscribers-backend-powerpc

Author: None (llvmbot)

Changes

Backport d07f106

Requested by: @syzaara

---

Full diff: https://github.com/llvm/llvm-project/pull/103301.diff

2 Files Affected:

• (modified) llvm/lib/Target/PowerPC/PPCFrameLowering.cpp (+12-2)
• (modified) llvm/test/CodeGen/PowerPC/aix-base-pointer.ll (+5)

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)

[mandlebug]

LGTM.

[syzaara]

@tru Hi Tobias, can you please help to merge in this PR? Thanks!

[github-actions]

@syzaara (or anyone else). If you would like to add a note about this fix in the release notes (completely optional). Please reply to this comment with a one or two sentence description of the fix. When you are done, please add the release:note label to this PR.