[CodeGen] Don't check attrs for stack realign (#92564)

shouldRealignStack/canRealignStack are repeatedly called in PEI (through
hasStackRealignment). Checking function attributes is expensive, so
cache this data in the MachineFrameInfo, which had most data already.

This slightly changes the semantics of `MachineFrameInfo::ForcedRealign`
to be also true when the `stackrealign` attribute is set.

Author: aengelke

llvm/include/llvm/CodeGen/MachineFrameInfo.h

@@ -346,6 +346,8 @@ class MachineFrameInfo {
 
   MachineFrameInfo(const MachineFrameInfo &) = delete;
 
+  bool isStackRealignable() const { return StackRealignable; }
+
   /// Return true if there are any stack objects in this function.
   bool hasStackObjects() const { return !Objects.empty(); }
 
@@ -603,6 +605,12 @@ class MachineFrameInfo {
   /// Make sure the function is at least Align bytes aligned.
   void ensureMaxAlignment(Align Alignment);
 
+  /// Return true if stack realignment is forced by function attributes or if
+  /// the stack alignment.
+  bool shouldRealignStack() const {
+    return ForcedRealign || MaxAlignment > StackAlignment;
+  }
+
   /// Return true if this function adjusts the stack -- e.g.,
   /// when calling another function. This is only valid during and after
   /// prolog/epilog code insertion.

llvm/lib/CodeGen/MachineFunction.cpp

@@ -200,10 +200,11 @@ void MachineFunction::init() {
   // explicitly asked us not to.
   bool CanRealignSP = STI->getFrameLowering()->isStackRealignable() &&
                       !F.hasFnAttribute("no-realign-stack");
+  bool ForceRealignSP = F.hasFnAttribute(Attribute::StackAlignment) ||
+                        F.hasFnAttribute("stackrealign");
   FrameInfo = new (Allocator) MachineFrameInfo(
       getFnStackAlignment(STI, F), /*StackRealignable=*/CanRealignSP,
-      /*ForcedRealign=*/CanRealignSP &&
-          F.hasFnAttribute(Attribute::StackAlignment));
+      /*ForcedRealign=*/ForceRealignSP && CanRealignSP);
 
   setUnsafeStackSize(F, *FrameInfo);
 

llvm/lib/CodeGen/TargetRegisterInfo.cpp

@@ -474,16 +474,11 @@ bool TargetRegisterInfo::isCalleeSavedPhysReg(
 }
 
 bool TargetRegisterInfo::canRealignStack(const MachineFunction &MF) const {
-  return !MF.getFunction().hasFnAttribute("no-realign-stack");
+  return MF.getFrameInfo().isStackRealignable();
 }
 
 bool TargetRegisterInfo::shouldRealignStack(const MachineFunction &MF) const {
-  const MachineFrameInfo &MFI = MF.getFrameInfo();
-  const TargetFrameLowering *TFI = MF.getSubtarget().getFrameLowering();
-  const Function &F = MF.getFunction();
-  return F.hasFnAttribute("stackrealign") ||
-         (MFI.getMaxAlign() > TFI->getStackAlign()) ||
-         F.hasFnAttribute(Attribute::StackAlignment);
+  return MF.getFrameInfo().shouldRealignStack();
 }
 
 bool TargetRegisterInfo::regmaskSubsetEqual(const uint32_t *mask0,