[PATCH] D68542: [Mips] Always save RA when disabling frame pointer elimination

[James Clarke via Phabricator via llvm-commits]

jrtc27 created this revision.
jrtc27 added a reviewer: atanasyan.
Herald added subscribers: llvm-commits, hiraditya, arichardson, sdardis.
Herald added a project: LLVM.

This ensures that frame-based unwinding will continue to work when
calling a noreturn function; there is not much use having the caller's
frame pointer saved if you don't also have the caller's program counter.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D68542

Files:
  llvm/lib/Target/Mips/MipsSEFrameLowering.cpp
  llvm/test/CodeGen/Mips/no-frame-pointer-elim.ll


Index: llvm/test/CodeGen/Mips/no-frame-pointer-elim.ll
===================================================================
--- /dev/null
+++ llvm/test/CodeGen/Mips/no-frame-pointer-elim.ll
@@ -0,0 +1,37 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
+; RUN: llc -march=mips64 -relocation-model=static < %s \
+; RUN:   | FileCheck %s --check-prefix STATIC
+; RUN: llc -march=mips64 -relocation-model=pic < %s \
+; RUN:   | FileCheck %s --check-prefix PIC
+
+declare dso_local void @callee() noreturn nounwind
+
+define dso_local void @caller() nounwind "no-frame-pointer-elim-non-leaf" {
+; STATIC-LABEL: caller:
+; STATIC:       # %bb.0: # %entry
+; STATIC-NEXT:    daddiu $sp, $sp, -16
+; STATIC-NEXT:    sd $ra, 8($sp) # 8-byte Folded Spill
+; STATIC-NEXT:    sd $fp, 0($sp) # 8-byte Folded Spill
+; STATIC-NEXT:    move $fp, $sp
+; STATIC-NEXT:    jal callee
+; STATIC-NEXT:    nop
+;
+; PIC-LABEL: caller:
+; PIC:       # %bb.0: # %entry
+; PIC-NEXT:    daddiu $sp, $sp, -32
+; PIC-NEXT:    sd $ra, 24($sp) # 8-byte Folded Spill
+; PIC-NEXT:    sd $fp, 16($sp) # 8-byte Folded Spill
+; PIC-NEXT:    sd $gp, 8($sp) # 8-byte Folded Spill
+; PIC-NEXT:    move $fp, $sp
+; PIC-NEXT:    lui $1, %hi(%neg(%gp_rel(caller)))
+; PIC-NEXT:    daddu $1, $1, $25
+; PIC-NEXT:    daddiu $gp, $1, %lo(%neg(%gp_rel(caller)))
+; PIC-NEXT:    ld $25, %call16(callee)($gp)
+; PIC-NEXT:    .reloc .Ltmp0, R_MIPS_JALR, callee
+; PIC-NEXT:  .Ltmp0:
+; PIC-NEXT:    jalr $25
+; PIC-NEXT:    nop
+entry:
+  tail call void @callee()
+  unreachable
+}
Index: llvm/lib/Target/Mips/MipsSEFrameLowering.cpp
===================================================================
--- llvm/lib/Target/Mips/MipsSEFrameLowering.cpp
+++ llvm/lib/Target/Mips/MipsSEFrameLowering.cpp
@@ -865,12 +865,15 @@
   const TargetRegisterInfo *TRI = MF.getSubtarget().getRegisterInfo();
   MipsFunctionInfo *MipsFI = MF.getInfo<MipsFunctionInfo>();
   MipsABIInfo ABI = STI.getABI();
+  unsigned RA = ABI.IsN64() ? Mips::RA_64 : Mips::RA;
   unsigned FP = ABI.GetFramePtr();
   unsigned BP = ABI.IsN64() ? Mips::S7_64 : Mips::S7;
 
-  // Mark $fp as used if function has dedicated frame pointer.
-  if (hasFP(MF))
+  // Mark $ra and $fp as used if function has dedicated frame pointer.
+  if (hasFP(MF)) {
+    setAliasRegs(MF, SavedRegs, RA);
     setAliasRegs(MF, SavedRegs, FP);
+  }
   // Mark $s7 as used if function has dedicated base pointer.
   if (hasBP(MF))
     setAliasRegs(MF, SavedRegs, BP);


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