[PATCH] D46110: [IR] Do not assume that function pointers are aligned

[Mikhail Maltsev via Phabricator via llvm-commits]

miyuki updated this revision to Diff 144147.
miyuki added a comment.

Added a comment


https://reviews.llvm.org/D46110

Files:
  lib/IR/Value.cpp
  test/Analysis/ValueTracking/func-ptr-lsb.ll


Index: test/Analysis/ValueTracking/func-ptr-lsb.ll
===================================================================
--- /dev/null
+++ test/Analysis/ValueTracking/func-ptr-lsb.ll
@@ -0,0 +1,18 @@
+; RUN: opt -instcombine -S < %s | FileCheck %s
+
+target datalayout = "e-p:32:32-n32-S64"
+
+; CHECK-LABEL: @foo_ptr
+; CHECK: and
+define i32 @foo_ptr() {
+entry:
+  ; Even though the address of @foo is aligned, we cannot assume that the
+  ; pointer has the same alignment. This is not true for e.g. ARM targets
+  ; which store ARM/Thumb state in the LSB
+  ret i32 and (i32 ptrtoint (void ()* @foo to i32), i32 -4)
+}
+
+define internal void @foo() align 16 {
+entry:
+  ret void
+}
Index: lib/IR/Value.cpp
===================================================================
--- lib/IR/Value.cpp
+++ lib/IR/Value.cpp
@@ -685,6 +685,10 @@
 
   unsigned Align = 0;
   if (auto *GO = dyn_cast<GlobalObject>(this)) {
+    // Don't make any assumptions about function pointer alignment. Some
+    // targets use the LSBs to store additional information.
+    if (isa<Function>(GO))
+      return 0;
     Align = GO->getAlignment();
     if (Align == 0) {
       if (auto *GVar = dyn_cast<GlobalVariable>(GO)) {


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