Revert 142337. Thumb1 still doesn't support dynamic stack realignment. :(

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@142557 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Target/ARM/ARMBaseRegisterInfo.cpp

@@ -626,10 +626,13 @@ bool ARMBaseRegisterInfo::hasBasePointer(const MachineFunction &MF) const {
 
 bool ARMBaseRegisterInfo::canRealignStack(const MachineFunction &MF) const {
   const MachineFrameInfo *MFI = MF.getFrameInfo();
+  const ARMFunctionInfo *AFI = MF.getInfo<ARMFunctionInfo>();
   // We can't realign the stack if:
   // 1. Dynamic stack realignment is explicitly disabled,
-  // 2. There are VLAs in the function and the base pointer is disabled.
-  return (RealignStack && (!MFI->hasVarSizedObjects() || EnableBasePointer));
+  // 2. This is a Thumb1 function (it's not useful, so we don't bother), or
+  // 3. There are VLAs in the function and the base pointer is disabled.
+  return (RealignStack && !AFI->isThumb1OnlyFunction() &&
+          (!MFI->hasVarSizedObjects() || EnableBasePointer));
 }
 
 bool ARMBaseRegisterInfo::

lib/Target/ARM/ARMFrameLowering.cpp

@@ -881,12 +881,10 @@ ARMFrameLowering::processFunctionBeforeCalleeSavedScan(MachineFunction &MF,
     // for sure what the stack size will be, but for this, an estimate is good
     // enough. If there anything changes it, it'll be a spill, which implies
     // we've used all the registers and so R4 is already used, so not marking
-    // it here will be OK.  Also spill R4 if Thumb1 function requires stack
-    // realignment.
+    // it here will be OK.
     // FIXME: It will be better just to find spare register here.
     unsigned StackSize = estimateStackSize(MF);
-    if (MFI->hasVarSizedObjects() || RegInfo->needsStackRealignment(MF) ||
-        StackSize > 508)
+    if (MFI->hasVarSizedObjects() || StackSize > 508)
       MF.getRegInfo().setPhysRegUsed(ARM::R4);
   }
 

lib/Target/ARM/Thumb1FrameLowering.cpp

@@ -155,32 +155,10 @@ void Thumb1FrameLowering::emitPrologue(MachineFunction &MF) const {
   AFI->setGPRCalleeSavedArea2Size(GPRCS2Size);
   AFI->setDPRCalleeSavedAreaSize(DPRCSSize);
 
-  // If we need dynamic stack realignment, do it here. Be paranoid and make
-  // sure if we also have VLAs, we have a base pointer for frame access.
-  if (RegInfo->needsStackRealignment(MF)) {
-    // We cannot use sp as source/dest register here, thus we're emitting the
-    // following sequence:
-    // mov r4, sp
-    // lsrs r4, r4, Log2MaxAlign
-    // lsls r4, r4, Log2MaxAlign
-    // mov sp, r4
-    unsigned MaxAlign = MFI->getMaxAlignment();
-    unsigned Log2MaxAlign = Log2_32(MaxAlign);
-    AddDefaultPred(BuildMI(MBB, MBBI, dl, TII.get(ARM::tMOVr), ARM::R4)
-                   .addReg(ARM::SP, RegState::Kill));
-    AddDefaultPred(AddDefaultT1CC(BuildMI(MBB, MBBI, dl, TII.get(ARM::tLSRri),
-                                          ARM::R4))
-                   .addReg(ARM::R4, RegState::Kill)
-                   .addImm(Log2MaxAlign));
-    AddDefaultPred(AddDefaultT1CC(BuildMI(MBB, MBBI, dl, TII.get(ARM::tLSLri),
-                                          ARM::R4))
-                   .addReg(ARM::R4, RegState::Kill)
-                   .addImm(Log2MaxAlign));
-    AddDefaultPred(BuildMI(MBB, MBBI, dl, TII.get(ARM::tMOVr), ARM::SP)
-                   .addReg(ARM::R4, RegState::Kill));
-
-    AFI->setShouldRestoreSPFromFP(true);    
-  }
+  // Thumb1 does not currently support dynamic stack realignment.  Report a
+  // fatal error rather then silently generate bad code.
+  if (RegInfo->needsStackRealignment(MF))
+      report_fatal_error("Dynamic stack realignment not supported for thumb1.");
 
   // If we need a base pointer, set it up here. It's whatever the value
   // of the stack pointer is at this point. Any variable size objects

test/CodeGen/ARM/thumb1-dynrealign.ll

@@ -1,40 +0,0 @@
-; RUN: llc < %s -mtriple=thumbv6-apple-darwin | FileCheck %s
-
-; Normal load from SP
-define void @SP(i32 %i) nounwind uwtable ssp {
-entry:
-; CHECK: @SP
-; CHECK: push	{r7, lr}
-; CHECK-NEXT: mov r7, sp
-; CHECK-NEXT: sub sp, #4
-; CHECK-NEXT: mov r1, sp 
-; CHECK-NEXT: str r0, [r1]
-; CHECK-NEXT: mov r0, sp
-; CHECK-NEXT: blx _SP_
-; CHECK-NEXT: add sp, #4
-; CHECK-NEXT: pop {r7, pc}
-  %i.addr = alloca i32, align 4
-  store i32 %i, i32* %i.addr, align 4
-  call void @SP_(i32* %i.addr)
-  ret void
-}
-
-declare void @SP_(i32*)
-
-; Dynamic stack realignment
-define void @FP(double %a) nounwind uwtable ssp {
-entry:
-; CHECK: mov r4, sp
-; CHECK-NEXT: lsrs r4, r4, #3
-; CHECK-NEXT: lsls r4, r4, #3
-; CHECK-NEXT: mov sp, r4
-; Restore from FP
-; CHECK: subs r4, r7, #4
-; CHECK: mov sp, r4
-  %a.addr = alloca double, align 8
-  store double %a, double* %a.addr, align 8
-  call void @FP_(double* %a.addr)
-  ret void
-}
-
-declare void @FP_(double*)