Targets: commonize some stack realignment code

This patch does the following:
* Fix FIXME on `needsStackRealignment`: it is now shared between multiple targets, implemented in `TargetRegisterInfo`, and isn't `virtual` anymore. This will break out-of-tree targets, silently if they used `virtual` and with a build error if they used `override`.
* Factor out `canRealignStack` as a `virtual` function on `TargetRegisterInfo`, by default only looks for the `no-realign-stack` function attribute.

Multiple targets duplicated the same `needsStackRealignment` code:
 - Aarch64.
 - ARM.
 - Mips almost: had extra `DEBUG` diagnostic, which the default implementation now has.
 - PowerPC.
 - WebAssembly.
 - x86 almost: has an extra `-force-align-stack` option, which the default implementation now has.

The default implementation of `needsStackRealignment` used to just return `false`. My current patch changes the behavior by simply using the above shared behavior. This affects:
 - AMDGPU
 - BPF
 - CppBackend
 - MSP430
 - NVPTX
 - Sparc
 - SystemZ
 - XCore
 - Out-of-tree targets
This is a breaking change! `make check` passes.

The only implementation of the `virtual` function (besides the slight different in x86) was Hexagon (which did `MF.getFrameInfo()->getMaxAlignment() > 8`), and potentially some out-of-tree targets. Hexagon now uses the default implementation.

`needsStackRealignment` was being overwritten in `<Target>GenRegisterInfo.inc`, to return `false` as the default also did. That was odd and is now gone.

Reviewers: sunfish

Subscribers: aemerson, llvm-commits, jfb

Differential Revision: http://reviews.llvm.org/D11160

llvm-svn: 242727

1 files changed, 1 insertions, 22 deletions

diff --git a/llvm/lib/Target/X86/X86RegisterInfo.cpp b/llvm/lib/Target/X86/X86RegisterInfo.cpp
index d8495e53e0e..683248f6d42 100644
--- a/llvm/lib/Target/X86/X86RegisterInfo.cpp
+++ b/llvm/lib/Target/X86/X86RegisterInfo.cpp
@@ -44,12 +44,6 @@ using namespace llvm;
 #define GET_REGINFO_TARGET_DESC
 #include "X86GenRegisterInfo.inc"
 
-cl::opt<bool>
-ForceStackAlign("force-align-stack",
-                 cl::desc("Force align the stack to the minimum alignment"
-                           " needed for the function."),
-                 cl::init(false), cl::Hidden);
-
 static cl::opt<bool>
 EnableBasePointer("x86-use-base-pointer", cl::Hidden, cl::init(true),
           cl::desc("Enable use of a base pointer for complex stack frames"));
@@ -457,7 +451,7 @@ bool X86RegisterInfo::hasBasePointer(const MachineFunction &MF) const {
 }
 
 bool X86RegisterInfo::canRealignStack(const MachineFunction &MF) const {
-  if (MF.getFunction()->hasFnAttribute("no-realign-stack"))
+  if (!TargetRegisterInfo::canRealignStack(MF))
     return false;
 
   const MachineFrameInfo *MFI = MF.getFrameInfo();
@@ -475,21 +469,6 @@ bool X86RegisterInfo::canRealignStack(const MachineFunction &MF) const {
   return true;
 }
 
-bool X86RegisterInfo::needsStackRealignment(const MachineFunction &MF) const {
-  const MachineFrameInfo *MFI = MF.getFrameInfo();
-  const X86FrameLowering *TFI = getFrameLowering(MF);
-  const Function *F = MF.getFunction();
-  unsigned StackAlign = TFI->getStackAlignment();
-  bool requiresRealignment = ((MFI->getMaxAlignment() > StackAlign) ||
-                              F->hasFnAttribute(Attribute::StackAlignment));
-
-  // If we've requested that we force align the stack do so now.
-  if (ForceStackAlign)
-    return canRealignStack(MF);
-
-  return requiresRealignment && canRealignStack(MF);
-}
-
 bool X86RegisterInfo::hasReservedSpillSlot(const MachineFunction &MF,
                                            unsigned Reg, int &FrameIdx) const {
   // Since X86 defines assignCalleeSavedSpillSlots which always return true