[llvm-commits] [llvm] r78668 - in /llvm/trunk: lib/Analysis/ValueTracking.cpp test/Transforms/InstCombine/align-external.ll

[Dan Gohman]

Author: djg
Date: Tue Aug 11 10:50:03 2009
New Revision: 78668

URL: http://llvm.org/viewvc/llvm-project?rev=78668&view=rev
Log:
Don't assume that external global variables are aligned at their preferred
alignment. Only the minimum alignment guaranteed by the ABI may be assumed.

Added:
    llvm/trunk/test/Transforms/InstCombine/align-external.ll
Modified:
    llvm/trunk/lib/Analysis/ValueTracking.cpp

Modified: llvm/trunk/lib/Analysis/ValueTracking.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/ValueTracking.cpp?rev=78668&r1=78667&r2=78668&view=diff

==============================================================================
--- llvm/trunk/lib/Analysis/ValueTracking.cpp (original)
+++ llvm/trunk/lib/Analysis/ValueTracking.cpp Tue Aug 11 10:50:03 2009
@@ -81,8 +81,16 @@
   // The address of an aligned GlobalValue has trailing zeros.
   if (GlobalValue *GV = dyn_cast<GlobalValue>(V)) {
     unsigned Align = GV->getAlignment();
-    if (Align == 0 && TD && GV->getType()->getElementType()->isSized()) 
-      Align = TD->getPrefTypeAlignment(GV->getType()->getElementType());
+    if (Align == 0 && TD && GV->getType()->getElementType()->isSized()) {
+      const Type *ObjectType = GV->getType()->getElementType();
+      // If the object is defined in the current Module, we'll be giving
+      // it the preferred alignment. Otherwise, we have to assume that it
+      // may only have the minimum ABI alignment.
+      if (!GV->isDeclaration() && !GV->mayBeOverridden())
+        Align = TD->getPrefTypeAlignment(ObjectType);
+      else
+        Align = TD->getABITypeAlignment(ObjectType);
+    }
     if (Align > 0)
       KnownZero = Mask & APInt::getLowBitsSet(BitWidth,
                                               CountTrailingZeros_32(Align));

Added: llvm/trunk/test/Transforms/InstCombine/align-external.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/align-external.ll?rev=78668&view=auto

==============================================================================
--- llvm/trunk/test/Transforms/InstCombine/align-external.ll (added)
+++ llvm/trunk/test/Transforms/InstCombine/align-external.ll Tue Aug 11 10:50:03 2009
@@ -0,0 +1,22 @@
+; RUN: llvm-as < %s | opt -instcombine | llvm-dis | FileCheck %s
+
+; Don't assume that external global variables have their preferred
+; alignment. They may only have the ABI minimum alignment.
+
+; CHECK: %s = shl i64 %a, 3
+; CHECK: %r = or i64 %s, ptrtoint (i32* @A to i64)
+; CHECK: %q = add i64 %r, 1
+; CHECK: ret i64 %q
+
+target datalayout = "-i32:8:32"
+
+ at A = external global i32
+ at B = external global i32
+
+define i64 @foo(i64 %a) {
+  %t = ptrtoint i32* @A to i64
+  %s = shl i64 %a, 3
+  %r = or i64 %t, %s
+  %q = add i64 %r, 1
+  ret i64 %q
+}