[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

2 files changed, 20 insertions, 4 deletions

diff --git a/llvm/lib/Target/ARM/ARMAsmPrinter.cpp b/llvm/lib/Target/ARM/ARMAsmPrinter.cpp
index d3d79fe975b..e50bbc19515 100644
--- a/llvm/lib/Target/ARM/ARMAsmPrinter.cpp
+++ b/llvm/lib/Target/ARM/ARMAsmPrinter.cpp
@@ -1086,6 +1086,8 @@ void ARMAsmPrinter::EmitUnwindingInstruction(const MachineInstr *MI) {
     unsigned StartOp = 2 + 2;
     // Use all the operands.
     unsigned NumOffset = 0;
+    // Amount of SP adjustment folded into a push.
+    unsigned Pad = 0;
 
     switch (Opc) {
     default:
@@ -1107,6 +1109,16 @@ void ARMAsmPrinter::EmitUnwindingInstruction(const MachineInstr *MI) {
         // temporary to workaround PR11902.
         if (MO.isImplicit())
           continue;
+        // Registers, pushed as a part of folding an SP update into the
+        // push instruction are marked as undef and should not be
+        // restored when unwinding, because the function can modify the
+        // corresponding stack slots.
+        if (MO.isUndef()) {
+          assert(RegList.empty() &&
+                 "Pad registers must come before restored ones");
+          Pad += 4;
+          continue;
+        }
         RegList.push_back(MO.getReg());
       }
       break;
@@ -1118,8 +1130,12 @@ void ARMAsmPrinter::EmitUnwindingInstruction(const MachineInstr *MI) {
       RegList.push_back(SrcReg);
       break;
     }
-    if (MAI->getExceptionHandlingType() == ExceptionHandling::ARM)
+    if (MAI->getExceptionHandlingType() == ExceptionHandling::ARM) {
       ATS.emitRegSave(RegList, Opc == ARM::VSTMDDB_UPD);
+      // Account for the SP adjustment, folded into the push.
+      if (Pad)
+        ATS.emitPad(Pad);
+    }
   } else {
     // Changes of stack / frame pointer.
     if (SrcReg == ARM::SP) {
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;