Verify parameter alignment attribute

[LuoYuanke]

Summary

In DAGISel, the parameter alignment only have 4 bits to hold the value.
The encode(alignment) would plus the value by 1, so the max aligment that
ISel can support is 2^14. This patch verify align attribute for parameter.

[LuoYuanke]

Fix test case failure.

[pengfei]

llvm/lib/IR/Verifier.cpp

1826

I think we can put the check inside here:

if (Attrs.hasAttribute(Attribute::ByVal)) {
  if (Attrs.hasAttribute(Attribute::Alignment)) {
    ...
  }
  SmallPtrSet<Type *, 4> Visited;

1830

Do we need check for ByRef?

[LuoYuanke]

llvm/lib/IR/Verifier.cpp

1830

It seems align attribute doesn't affect ByRef. Run below code with "llc t.ll" doesn't crash.

define dso_local void @foo(i8* %p) {
entry:
  %p1 = bitcast i8* %p to <8 x float>*
  call void @bar(<8 x float>* noundef byref(<8 x float>) align 32768 %p1)
  ret void
}

declare dso_local void @bar(<8 x float>* %p)

In https://llvm.org/docs/LangRef.html, it says Note that this attribute has additional semantics when combined with the byval or preallocated attribute, which are documented there.

[LuoYuanke]

Address Phoebe's comments.

[craig.topper]

llvm/lib/IR/Verifier.cpp

1818

ArgFlagsTy -> ISD::ArgFlagsTy

[LuoYuanke]

Address Craig's comments.

[pengfei]

LGTM.

llvm/lib/IR/Verifier.cpp

1821

Missing the period .

[LuoYuanke]

Address Phoebe's comments.

[skan]

llvm/lib/IR/Verifier.cpp

1819

The Align(1<<15) and comments here are duplicated in D121898, I suggest that you add Align(1<<15) as a const static member of Verifier, and move the comments to the position of the definition. The we can avoid duplicated code.

[LuoYuanke]

llvm/lib/IR/Verifier.cpp

1819

Good suggestion. I apply your suggestion in https://reviews.llvm.org/D121898. Will update this patch after D121898 land.

llvm/lib/IR/Verifier.cpp

if (!Attr.isStringAttribute() &&
       CheckFailed("Attribute '" + Attr.getAsString() +
                   "' applied to incompatible type!", V);
       return;
     }
   }
 
   if (PointerType *PTy = dyn_cast<PointerType>(Ty)) {
     if (Attrs.hasAttribute(Attribute::ByVal)) {
+      if (Attrs.hasAttribute(Attribute::Alignment)) {
+        Align AttrAlign = Attrs.getAlignment().valueOrOne();
+        // ISD::ArgFlagsTy::MemAlign only have 4 bits for alignment, so
+        // the alignment size should not exceed 2^15. Since encode(Align)
+        // would plus the shift value by 1, the alignment size should
+        // not exceed 2^14, otherwise it can NOT be properly lowered.
+        Align MaxAlign(1 << 15);
+        Assert(AttrAlign < MaxAlign,
+               "Attribute 'align' exceed the max size 2^14", V);
+      }
       SmallPtrSet<Type *, 4> Visited;
       Assert(Attrs.getByValType()->isSized(&Visited),
              "Attribute 'byval' does not support unsized types!", V);
     }
     if (Attrs.hasAttribute(Attribute::ByRef)) {
       SmallPtrSet<Type *, 4> Visited;
       Assert(Attrs.getByRefType()->isSized(&Visited),
              "Attribute 'byref' does not support unsized types!", V);
     }
     if (Attrs.hasAttribute(Attribute::InAlloca)) {
       SmallPtrSet<Type *, 4> Visited;
       Assert(Attrs.getInAllocaType()->isSized(&Visited),
              "Attribute 'inalloca' does not support unsized types!", V);

llvm/test/Verifier/param-attr-align.ll

+; RUN: not llvm-as < %s 2>&1 | FileCheck %s
+
+; CHECK: Attribute 'align' exceed the max size 2^14
+define dso_local void @foo(i8* %p) {
+entry:
+  %p1 = bitcast i8* %p to <8 x float>*
+  call void @bar(<8 x float>* noundef byval(<8 x float>) align 32768 %p1)
+  ret void
+}
+
+declare dso_local void @bar(<8 x float>* %p)