Calculate __builtin_object_size when pointer depends on a condition

This patch fixes calculating of builtin_object_size if it depends on a
condition. Before this patch compiler did not know how to calculate the
object size when it finds a condition that cannot be eliminated.
This patch enables calculating of builtin_object_size even in case when
condition cannot be eliminated by choosing minimum or maximum value as a
result from condition. Choosing minimum or maximum value from condition
is based on the second argument of __builtin_object_size function.

Patch by Strahinja Petrovic.

Differential Revision: http://reviews.llvm.org/D18438

llvm-svn: 266193

1 files changed, 12 insertions, 3 deletions

diff --git a/llvm/lib/CodeGen/CodeGenPrepare.cpp b/llvm/lib/CodeGen/CodeGenPrepare.cpp
index e9e6146c759..ea1325a8627 100644
--- a/llvm/lib/CodeGen/CodeGenPrepare.cpp
+++ b/llvm/lib/CodeGen/CodeGenPrepare.cpp
@@ -22,6 +22,7 @@
 #include "llvm/Analysis/TargetLibraryInfo.h"
 #include "llvm/Analysis/TargetTransformInfo.h"
 #include "llvm/Analysis/ValueTracking.h"
+#include "llvm/Analysis/MemoryBuiltins.h"
 #include "llvm/IR/CallSite.h"
 #include "llvm/IR/Constants.h"
 #include "llvm/IR/DataLayout.h"
@@ -1807,10 +1808,18 @@ bool CodeGenPrepare::optimizeCallInst(CallInst *CI, bool& ModifiedDT) {
     default: break;
     case Intrinsic::objectsize: {
       // Lower all uses of llvm.objectsize.*
-      bool Min = (cast<ConstantInt>(II->getArgOperand(1))->getZExtValue() == 1);
+      uint64_t Size;
       Type *ReturnTy = CI->getType();
-      Constant *RetVal = ConstantInt::get(ReturnTy, Min ? 0 : -1ULL);
-
+      Constant *RetVal = nullptr;
+      ConstantInt *Op1 = cast<ConstantInt>(II->getArgOperand(1));
+      ObjSizeMode Mode = Op1->isZero() ? ObjSizeMode::Max : ObjSizeMode::Min;
+      if (getObjectSize(II->getArgOperand(0),
+                        Size, *DL, TLInfo, false, Mode)) {
+        RetVal = ConstantInt::get(ReturnTy, Size);
+      } else {
+        RetVal = ConstantInt::get(ReturnTy,
+                                  Mode == ObjSizeMode::Min ? 0 : -1ULL);
+      }
       // Substituting this can cause recursive simplifications, which can
       // invalidate our iterator.  Use a WeakVH to hold onto it in case this
       // happens.