[InstCombineCalls] Optimize call of bitcast even w/ parameter attributes

Before we gave up if a call through bitcast had parameter attributes.
Interestingly, we allowed attributes for the return value already. We
now handle both the same way, namely, we drop the ones that are
incompatible with the new type and keep the rest. This cannot cause
"more UB" than initially present.

Differential Revision: https://reviews.llvm.org/D119967

1 files changed, 36 insertions, 26 deletions

diff --git a/llvm/lib/IR/Attributes.cpp b/llvm/lib/IR/Attributes.cpp
index 767767c..c4759f8 100644
--- a/llvm/lib/IR/Attributes.cpp
+++ b/llvm/lib/IR/Attributes.cpp
@@ -1773,40 +1773,50 @@ bool AttrBuilder::operator==(const AttrBuilder &B) const {
 //===----------------------------------------------------------------------===//
 
 /// Which attributes cannot be applied to a type.
-AttributeMask AttributeFuncs::typeIncompatible(Type *Ty) {
+AttributeMask AttributeFuncs::typeIncompatible(Type *Ty,
+                                               AttributeSafetyKind ASK) {
   AttributeMask Incompatible;
 
-  if (!Ty->isIntegerTy())
+  if (!Ty->isIntegerTy()) {
     // Attributes that only apply to integers.
-    Incompatible.addAttribute(Attribute::SExt)
-        .addAttribute(Attribute::ZExt)
-        .addAttribute(Attribute::AllocAlign);
+    if (ASK & ASK_SAFE_TO_DROP)
+      Incompatible.addAttribute(Attribute::AllocAlign);
+    if (ASK & ASK_UNSAFE_TO_DROP)
+      Incompatible.addAttribute(Attribute::SExt).addAttribute(Attribute::ZExt);
+  }
 
-  if (!Ty->isPointerTy())
+  if (!Ty->isPointerTy()) {
     // Attributes that only apply to pointers.
-    Incompatible.addAttribute(Attribute::Nest)
-        .addAttribute(Attribute::NoAlias)
-        .addAttribute(Attribute::NoCapture)
-        .addAttribute(Attribute::NonNull)
-        .addAttribute(Attribute::ReadNone)
-        .addAttribute(Attribute::ReadOnly)
-        .addAttribute(Attribute::SwiftError)
-        .addAttribute(Attribute::Dereferenceable)
-        .addAttribute(Attribute::DereferenceableOrNull)
-        .addAttribute(Attribute::Preallocated)
-        .addAttribute(Attribute::InAlloca)
-        .addAttribute(Attribute::ByVal)
-        .addAttribute(Attribute::StructRet)
-        .addAttribute(Attribute::ByRef)
-        .addAttribute(Attribute::ElementType);
-
-  if (!Ty->isPtrOrPtrVectorTy())
+    if (ASK & ASK_SAFE_TO_DROP)
+      Incompatible.addAttribute(Attribute::NoAlias)
+          .addAttribute(Attribute::NoCapture)
+          .addAttribute(Attribute::NonNull)
+          .addAttribute(Attribute::ReadNone)
+          .addAttribute(Attribute::ReadOnly)
+          .addAttribute(Attribute::Dereferenceable)
+          .addAttribute(Attribute::DereferenceableOrNull);
+    if (ASK & ASK_UNSAFE_TO_DROP)
+      Incompatible.addAttribute(Attribute::Nest)
+          .addAttribute(Attribute::SwiftError)
+          .addAttribute(Attribute::Preallocated)
+          .addAttribute(Attribute::InAlloca)
+          .addAttribute(Attribute::ByVal)
+          .addAttribute(Attribute::StructRet)
+          .addAttribute(Attribute::ByRef)
+          .addAttribute(Attribute::ElementType);
+  }
+
     // Attributes that only apply to pointers or vectors of pointers.
-    Incompatible.addAttribute(Attribute::Alignment);
+  if (!Ty->isPtrOrPtrVectorTy()) {
+    if (ASK & ASK_SAFE_TO_DROP)
+      Incompatible.addAttribute(Attribute::Alignment);
+  }
 
   // Some attributes can apply to all "values" but there are no `void` values.
-  if (Ty->isVoidTy())
-    Incompatible.addAttribute(Attribute::NoUndef);
+  if (Ty->isVoidTy()) {
+    if (ASK & ASK_SAFE_TO_DROP)
+      Incompatible.addAttribute(Attribute::NoUndef);
+  }
 
   return Incompatible;
 }