[llvm] r321996 - [ARM] Fix PR35379 - incorrect unwind information when compiling with -Oz

[Momchil Velikov via llvm-commits]

Author: chill
Date: Mon Jan  8 06:47:19 2018
New Revision: 321996

URL: http://llvm.org/viewvc/llvm-project?rev=321996&view=rev
Log:
[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


Added:
    llvm/trunk/test/CodeGen/ARM/PR35379.ll
Modified:
    llvm/trunk/lib/Target/ARM/ARMAsmPrinter.cpp
    llvm/trunk/lib/Target/ARM/ARMBaseInstrInfo.cpp

Modified: llvm/trunk/lib/Target/ARM/ARMAsmPrinter.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/ARM/ARMAsmPrinter.cpp?rev=321996&r1=321995&r2=321996&view=diff
==============================================================================
--- llvm/trunk/lib/Target/ARM/ARMAsmPrinter.cpp (original)
+++ llvm/trunk/lib/Target/ARM/ARMAsmPrinter.cpp Mon Jan  8 06:47:19 2018
@@ -1086,6 +1086,8 @@ void ARMAsmPrinter::EmitUnwindingInstruc
     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::EmitUnwindingInstruc
         // 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::EmitUnwindingInstruc
       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) {

Modified: llvm/trunk/lib/Target/ARM/ARMBaseInstrInfo.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/ARM/ARMBaseInstrInfo.cpp?rev=321996&r1=321995&r2=321996&view=diff
==============================================================================
--- llvm/trunk/lib/Target/ARM/ARMBaseInstrInfo.cpp (original)
+++ llvm/trunk/lib/Target/ARM/ARMBaseInstrInfo.cpp Mon Jan  8 06:47:19 2018
@@ -2277,9 +2277,9 @@ bool llvm::tryFoldSPUpdateIntoPushPop(co
        --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;

Added: llvm/trunk/test/CodeGen/ARM/PR35379.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/ARM/PR35379.ll?rev=321996&view=auto
==============================================================================
--- llvm/trunk/test/CodeGen/ARM/PR35379.ll (added)
+++ llvm/trunk/test/CodeGen/ARM/PR35379.ll Mon Jan  8 06:47:19 2018
@@ -0,0 +1,52 @@
+; RUN: llc -mtriple=armv7a-eabi < %s | FileCheck %s --check-prefix=CHECK-ARM
+; RUN: llc -mtriple=armv6m-eabi < %s | FileCheck %s --check-prefix=CHECK-THM
+
+; Function Attrs: minsize optsize
+declare void @g(i32*) local_unnamed_addr #0
+
+; Function Attrs: minsize optsize
+define void @f() local_unnamed_addr #0 {
+entry:
+  %i = alloca i32, align 4
+  %0 = bitcast i32* %i to i8*
+  store i32 1, i32* %i, align 4
+  call void @g(i32* nonnull %i)
+  ret void
+}
+
+; Check unwind info does not mention the registers used for padding, and
+; the amount of stack adjustment is the same as in the actual
+; instructions.
+
+; CHECK-ARM:      .save {r11, lr}
+; CHECK-ARM-NEXT: .pad #8
+; CHECK-ARM-NEXT: push {r9, r10, r11, lr}
+; CHECK-ARM:      pop {r2, r3, r11, pc}
+
+; CHECK-THM:      .save {r7, lr}
+; CHECK-THM-NEXT: .pad #8
+; CHECK-THM-NEXT: push {r5, r6, r7, lr}
+; CHECK-THM:      pop {r2, r3, r7, pc}
+
+
+define void @f1() local_unnamed_addr #1 {
+entry:
+  %i = alloca i32, align 4
+  %0 = bitcast i32* %i to i8*
+  store i32 1, i32* %i, align 4
+  call void @g(i32* nonnull %i)
+  ret void
+}
+
+; Check that unwind info is the same whether or not using -Os (minsize attr)
+
+; CHECK-ARM:      .save {r11, lr}
+; CHECK-ARM-NEXT: push {r11, lr}
+; CHECK-ARM-NEXT: .pad #8
+
+; CHECK-THM:      .save {r7, lr}
+; CHECK-THM-NEXT: push {r7, lr}
+; CHECK-THM-NEXT: .pad #8
+
+attributes #0 = { minsize optsize }
+attributes #1 = { optsize }