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, 10 insertions, 39 deletions

diff --git a/llvm/lib/Target/Mips/MipsRegisterInfo.cpp b/llvm/lib/Target/Mips/MipsRegisterInfo.cpp
index f6647e6a846..775d8006fdf 100644
--- a/llvm/lib/Target/Mips/MipsRegisterInfo.cpp
+++ b/llvm/lib/Target/Mips/MipsRegisterInfo.cpp
@@ -284,6 +284,16 @@ getFrameRegister(const MachineFunction &MF) const {
 }
 
 bool MipsRegisterInfo::canRealignStack(const MachineFunction &MF) const {
+  // Avoid realigning functions that explicitly do not want to be realigned.
+  // Normally, we should report an error when a function should be dynamically
+  // realigned but also has the attribute no-realign-stack. Unfortunately,
+  // with this attribute, MachineFrameInfo clamps each new object's alignment
+  // to that of the stack's alignment as specified by the ABI. As a result,
+  // the information of whether we have objects with larger alignment
+  // requirement than the stack's alignment is already lost at this point.
+  if (!TargetRegisterInfo::canRealignStack(MF))
+    return false;
+
   const MipsSubtarget &Subtarget = MF.getSubtarget<MipsSubtarget>();
   unsigned FP = Subtarget.isGP32bit() ? Mips::FP : Mips::FP_64;
   unsigned BP = Subtarget.isGP32bit() ? Mips::S7 : Mips::S7_64;
@@ -306,42 +316,3 @@ bool MipsRegisterInfo::canRealignStack(const MachineFunction &MF) const {
   // sized objects.
   return MF.getRegInfo().canReserveReg(BP);
 }
-
-bool MipsRegisterInfo::needsStackRealignment(const MachineFunction &MF) const {
-  const MipsSubtarget &Subtarget = MF.getSubtarget<MipsSubtarget>();
-  const MachineFrameInfo *MFI = MF.getFrameInfo();
-
-  bool CanRealign = canRealignStack(MF);
-
-  // Avoid realigning functions that explicitly do not want to be realigned.
-  // Normally, we should report an error when a function should be dynamically
-  // realigned but also has the attribute no-realign-stack. Unfortunately,
-  // with this attribute, MachineFrameInfo clamps each new object's alignment
-  // to that of the stack's alignment as specified by the ABI. As a result,
-  // the information of whether we have objects with larger alignment
-  // requirement than the stack's alignment is already lost at this point.
-  if (MF.getFunction()->hasFnAttribute("no-realign-stack"))
-    return false;
-
-  const Function *F = MF.getFunction();
-  if (F->hasFnAttribute(Attribute::StackAlignment)) {
-#ifdef DEBUG
-    if (!CanRealign)
-      DEBUG(dbgs() << "It's not possible to realign the stack of the function: "
-            << F->getName() << "\n");
-#endif
-    return CanRealign;
-  }
-
-  unsigned StackAlignment = Subtarget.getFrameLowering()->getStackAlignment();
-  if (MFI->getMaxAlignment() > StackAlignment) {
-#ifdef DEBUG
-    if (!CanRealign)
-      DEBUG(dbgs() << "It's not possible to realign the stack of the function: "
-            << F->getName() << "\n");
-#endif
-    return CanRealign;
-  }
-
-  return false;
-}