[ARM] Fix PR35379 - incorrect unwind information when compiling with -Oz

The patch makes the unwind information not mention registers, which were pushed
solely for the purpose of saving stack adjustment instructions.

Differential revision: https://reviews.llvm.org/D41300
Fixes https://bugs.llvm.org/show_bug.cgi?id=35379

llvm-svn: 321996

1 files changed, 3 insertions, 3 deletions

diff --git a/llvm/lib/Target/ARM/ARMBaseInstrInfo.cpp b/llvm/lib/Target/ARM/ARMBaseInstrInfo.cpp
index 8c1727724a9..7bf47ab6060 100644
--- a/llvm/lib/Target/ARM/ARMBaseInstrInfo.cpp
+++ b/llvm/lib/Target/ARM/ARMBaseInstrInfo.cpp
@@ -2277,9 +2277,9 @@ bool llvm::tryFoldSPUpdateIntoPushPop(const ARMSubtarget &Subtarget,
        --CurRegEnc) {
     unsigned CurReg = RegClass->getRegister(CurRegEnc);
     if (!IsPop) {
-      // Pushing any register is completely harmless, mark the
-      // register involved as undef since we don't care about it in
-      // the slightest.
+      // Pushing any register is completely harmless, mark the register involved
+      // as undef since we don't care about its value and must not restore it
+      // during stack unwinding.
       RegList.push_back(MachineOperand::CreateReg(CurReg, false, false,
                                                   false, false, true));
       --RegsNeeded;