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, 0 insertions, 2 deletions

diff --git a/llvm/lib/Target/PowerPC/PPCRegisterInfo.h b/llvm/lib/Target/PowerPC/PPCRegisterInfo.h
index d304e1d..cd25b0e 100644
--- a/llvm/lib/Target/PowerPC/PPCRegisterInfo.h
+++ b/llvm/lib/Target/PowerPC/PPCRegisterInfo.h
@@ -136,8 +136,6 @@ public:
   // Base pointer (stack realignment) support.
   unsigned getBaseRegister(const MachineFunction &MF) const;
   bool hasBasePointer(const MachineFunction &MF) const;
-  bool canRealignStack(const MachineFunction &MF) const;
-  bool needsStackRealignment(const MachineFunction &MF) const override;
 };
 
 } // end namespace llvm