[PATCH] D100879: [Clang] Propagate guaranteed alignment for malloc and others

[Dávid Bolvanský via Phabricator via cfe-commits]

xbolva00 created this revision.
xbolva00 added reviewers: aaron.ballman, rjmccall.
xbolva00 requested review of this revision.
Herald added a project: clang.
Herald added a subscriber: cfe-commits.

LLVM should be smarter about *known* malloc's alignment and this knowledge may enable other optimizations.

Originally started as LLVM patch - https://reviews.llvm.org/D100862 but this logic should be really in Clang.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D100879

Files:
  clang/lib/CodeGen/CGCall.cpp
  clang/lib/Sema/SemaDecl.cpp


Index: clang/lib/Sema/SemaDecl.cpp
===================================================================
--- clang/lib/Sema/SemaDecl.cpp
+++ clang/lib/Sema/SemaDecl.cpp
@@ -45,6 +45,7 @@
 #include "clang/Sema/Template.h"
 #include "llvm/ADT/SmallString.h"
 #include "llvm/ADT/Triple.h"
+ #include "llvm/IR/Attributes.h"
 #include <algorithm>
 #include <cstring>
 #include <functional>
Index: clang/lib/CodeGen/CGCall.cpp
===================================================================
--- clang/lib/CodeGen/CGCall.cpp
+++ clang/lib/CodeGen/CGCall.cpp
@@ -2048,6 +2048,22 @@
       // allows it to work on indirect virtual function calls.
       if (AttrOnCallSite && TargetDecl->hasAttr<NoMergeAttr>())
         FuncAttrs.addAttribute(llvm::Attribute::NoMerge);
+
+      // Add known guaranteed alignment for allocation functions
+      if (unsigned BuiltinID = Fn->getBuiltinID()) {
+        switch (BuiltinID) {
+        case Builtin::BImalloc:
+        case Builtin::BIcalloc:
+        case Builtin::BIrealloc:
+        case Builtin::BIstrdup:
+        case Builtin::BIstrndup:
+          RetAttrs.addAlignmentAttr(Context.getTargetInfo().getNewAlign() /
+                                    Context.getTargetInfo().getCharWidth());
+          break;
+        default:
+          break;
+        }
+      }
     }
 
     // 'const', 'pure' and 'noalias' attributed functions are also nounwind.


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