[llvm] a9b03d9 - [Attributor] Remove function pointer restriction for AAAlign

[Nikita Popov via llvm-commits]

Author: Nikita Popov
Date: 2022-03-07T10:02:45+01:00
New Revision: a9b03d9e2e3888ad08f9f0294c6e6bec43d7c884

URL: https://github.com/llvm/llvm-project/commit/a9b03d9e2e3888ad08f9f0294c6e6bec43d7c884
DIFF: https://github.com/llvm/llvm-project/commit/a9b03d9e2e3888ad08f9f0294c6e6bec43d7c884.diff

LOG: [Attributor] Remove function pointer restriction for AAAlign

This check is not compatible with opaque pointers. We can avoid
it by adjusting the getPointerAlignment() implementation to avoid
creating unnecessary ptrtoint expressions for bitcasted pointers.
The code already uses OnlyIfReduced to not create an expression
if it does not simplify, and this makes sure that folding a
bitcast and ptrtoint into a ptrtoint doesn't count as a
simplification.

Differential Revision: https://reviews.llvm.org/D120904

Added: 
    

Modified: 
    llvm/lib/IR/Value.cpp
    llvm/lib/Transforms/IPO/AttributorAttributes.cpp

Removed: 
    


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diff  --git a/llvm/lib/IR/Value.cpp b/llvm/lib/IR/Value.cpp
index df286df5a96a9..3348de6dcd2ef 100644
--- a/llvm/lib/IR/Value.cpp
+++ b/llvm/lib/IR/Value.cpp
@@ -964,6 +964,9 @@ Align Value::getPointerAlignment(const DataLayout &DL) const {
       return Align(CI->getLimitedValue());
     }
   } else if (auto *CstPtr = dyn_cast<Constant>(this)) {
+    // Strip pointer casts to avoid creating unnecessary ptrtoint expression
+    // if the only "reduction" is combining a bitcast + ptrtoint.
+    CstPtr = CstPtr->stripPointerCasts();
     if (auto *CstInt = dyn_cast_or_null<ConstantInt>(ConstantExpr::getPtrToInt(
             const_cast<Constant *>(CstPtr), DL.getIntPtrType(getType()),
             /*OnlyIfReduced=*/true))) {

diff  --git a/llvm/lib/Transforms/IPO/AttributorAttributes.cpp b/llvm/lib/Transforms/IPO/AttributorAttributes.cpp
index 9dbc845bdf4f9..2b616ae77884e 100644
--- a/llvm/lib/Transforms/IPO/AttributorAttributes.cpp
+++ b/llvm/lib/Transforms/IPO/AttributorAttributes.cpp
@@ -4521,13 +4521,7 @@ struct AAAlignImpl : AAAlign {
       takeKnownMaximum(Attr.getValueAsInt());
 
     Value &V = getAssociatedValue();
-    // TODO: This is a HACK to avoid getPointerAlignment to introduce a ptr2int
-    //       use of the function pointer. This was caused by D73131. We want to
-    //       avoid this for function pointers especially because we iterate
-    //       their uses and int2ptr is not handled. It is not a correctness
-    //       problem though!
-    if (!V.getType()->getPointerElementType()->isFunctionTy())
-      takeKnownMaximum(V.getPointerAlignment(A.getDataLayout()).value());
+    takeKnownMaximum(V.getPointerAlignment(A.getDataLayout()).value());
 
     if (getIRPosition().isFnInterfaceKind() &&
         (!getAnchorScope() ||