PNaCl ABI: Strip alignment info from memcpy/memmove/memset intrinsic calls

Do the same for memcpy/memmove/memset intrinsic calls that we have
already done for integer loads and stores: Remove assumptions about
pointer alignment by setting the alignment argument to 1.  Make the
ABI checker require this.

BUG=https://code.google.com/p/nativeclient/issues/detail?id=3445
TEST=*.ll tests + PNaCl toolchain trybots

Review URL: https://codereview.chromium.org/17563008

2 files changed, 21 insertions, 0 deletions

diff --git a/lib/Analysis/NaCl/PNaClABIVerifyFunctions.cpp b/lib/Analysis/NaCl/PNaClABIVerifyFunctions.cpp
index 1fe79757a0..9a96d19ed4 100644
--- a/lib/Analysis/NaCl/PNaClABIVerifyFunctions.cpp
+++ b/lib/Analysis/NaCl/PNaClABIVerifyFunctions.cpp
@@ -315,6 +315,18 @@ const char *PNaClABIVerifyFunctions::checkInstruction(const Instruction *Inst) {
                 isa<MDNode>(Arg)))
             return "bad intrinsic operand";
         }
+        // Disallow alignments other than 1 on memcpy() etc., for the
+        // same reason that we disallow them on integer loads and
+        // stores.
+        if (const MemIntrinsic *MemOp = dyn_cast<MemIntrinsic>(Call)) {
+          // Avoid the getAlignment() method here because it aborts if
+          // the alignment argument is not a Constant.
+          Value *AlignArg = MemOp->getArgOperand(3);
+          if (!isa<ConstantInt>(AlignArg) ||
+              cast<ConstantInt>(AlignArg)->getZExtValue() != 1) {
+            return "bad alignment";
+          }
+        }
         // Allow the instruction and skip the later checks.
         return NULL;
       }
diff --git a/lib/Transforms/NaCl/StripAttributes.cpp b/lib/Transforms/NaCl/StripAttributes.cpp
index 9c3dd6c83e..fb3a080e84 100644
--- a/lib/Transforms/NaCl/StripAttributes.cpp
+++ b/lib/Transforms/NaCl/StripAttributes.cpp
@@ -14,6 +14,7 @@
 //    calls.
 //  * Calling conventions from functions and function calls.
 //  * The "align" attribute on functions.
+//  * The alignment argument of memcpy/memmove/memset intrinsic calls.
 //  * The "unnamed_addr" attribute on functions and global variables.
 //  * The distinction between "internal" and "private" linkage.
 //  * "protected" and "internal" visibility of functions and globals.
@@ -25,6 +26,7 @@
 
 #include "llvm/IR/DataLayout.h"
 #include "llvm/IR/Function.h"
+#include "llvm/IR/IntrinsicInst.h"
 #include "llvm/IR/Module.h"
 #include "llvm/IR/Operator.h"
 #include "llvm/Pass.h"
@@ -182,6 +184,13 @@ void stripFunctionAttrs(DataLayout *DL, Function *Func) {
         CheckAttributes(Call.getAttributes());
         Call.setAttributes(AttributeSet());
         Call.setCallingConv(CallingConv::C);
+
+        // Set memcpy(), memmove() and memset() to use pessimistic
+        // alignment assumptions.
+        if (MemIntrinsic *MemOp = dyn_cast<MemIntrinsic>(Inst)) {
+          Type *AlignTy = MemOp->getAlignmentCst()->getType();
+          MemOp->setAlignment(ConstantInt::get(AlignTy, 1));
+        }
       } else if (OverflowingBinaryOperator *Op =
                      dyn_cast<OverflowingBinaryOperator>(Inst)) {
         cast<BinaryOperator>(Op)->setHasNoUnsignedWrap(false);