[llvm] r307754 - [MemoryBuiltins] Allow truncation in visitAllocaInst()

[Mikael Holmen via llvm-commits]

Author: uabelho
Date: Tue Jul 11 23:19:10 2017
New Revision: 307754

URL: http://llvm.org/viewvc/llvm-project?rev=307754&view=rev
Log:
[MemoryBuiltins] Allow truncation in visitAllocaInst()

Summary:
Solves PR33689.

If the pointer size is less than the size of the type used for the array
size in an alloca (the <ty> type below) then we could trigger the assert in
the PR. In that example we have pointer size i16 and <ty> is i32.

<result> = alloca [inalloca] <type> [, <ty> <NumElements>] [, align <alignment>]

Handle the situation by allowing truncation as well as zero extension in
ObjectSizeOffsetVisitor::visitAllocaInst().

Also, we now detect overflow in visitAllocaInst(), similar to how it was
already done in visitCallSite().

Reviewers: craig.topper, rnk, george.burgess.iv

Reviewed By: george.burgess.iv

Subscribers: davide, llvm-commits

Differential Revision: https://reviews.llvm.org/D35003

Modified:
    llvm/trunk/include/llvm/Analysis/MemoryBuiltins.h
    llvm/trunk/lib/Analysis/MemoryBuiltins.cpp

Modified: llvm/trunk/include/llvm/Analysis/MemoryBuiltins.h
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/Analysis/MemoryBuiltins.h?rev=307754&r1=307753&r2=307754&view=diff
==============================================================================
--- llvm/trunk/include/llvm/Analysis/MemoryBuiltins.h (original)
+++ llvm/trunk/include/llvm/Analysis/MemoryBuiltins.h Tue Jul 11 23:19:10 2017
@@ -224,6 +224,9 @@ public:
   SizeOffsetType visitSelectInst(SelectInst &I);
   SizeOffsetType visitUndefValue(UndefValue&);
   SizeOffsetType visitInstruction(Instruction &I);
+
+private:
+  bool CheckedZextOrTrunc(APInt &I);
 };
 
 typedef std::pair<Value*, Value*> SizeOffsetEvalType;

Modified: llvm/trunk/lib/Analysis/MemoryBuiltins.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/MemoryBuiltins.cpp?rev=307754&r1=307753&r2=307754&view=diff
==============================================================================
--- llvm/trunk/lib/Analysis/MemoryBuiltins.cpp (original)
+++ llvm/trunk/lib/Analysis/MemoryBuiltins.cpp Tue Jul 11 23:19:10 2017
@@ -505,6 +505,22 @@ SizeOffsetType ObjectSizeOffsetVisitor::
   return unknown();
 }
 
+/// When we're compiling N-bit code, and the user uses parameters that are
+/// greater than N bits (e.g. uint64_t on a 32-bit build), we can run into
+/// trouble with APInt size issues. This function handles resizing + overflow
+/// checks for us. Check and zext or trunc \p I depending on IntTyBits and
+/// I's value.
+bool ObjectSizeOffsetVisitor::CheckedZextOrTrunc(APInt &I) {
+  // More bits than we can handle. Checking the bit width isn't necessary, but
+  // it's faster than checking active bits, and should give `false` in the
+  // vast majority of cases.
+  if (I.getBitWidth() > IntTyBits && I.getActiveBits() > IntTyBits)
+    return false;
+  if (I.getBitWidth() != IntTyBits)
+    I = I.zextOrTrunc(IntTyBits);
+  return true;
+}
+
 SizeOffsetType ObjectSizeOffsetVisitor::visitAllocaInst(AllocaInst &I) {
   if (!I.getAllocatedType()->isSized())
     return unknown();
@@ -515,8 +531,14 @@ SizeOffsetType ObjectSizeOffsetVisitor::
 
   Value *ArraySize = I.getArraySize();
   if (const ConstantInt *C = dyn_cast<ConstantInt>(ArraySize)) {
-    Size *= C->getValue().zextOrSelf(IntTyBits);
-    return std::make_pair(align(Size, I.getAlignment()), Zero);
+    APInt NumElems = C->getValue();
+    if (!CheckedZextOrTrunc(NumElems))
+      return unknown();
+
+    bool Overflow;
+    Size = Size.umul_ov(NumElems, Overflow);
+    return Overflow ? unknown() : std::make_pair(align(Size, I.getAlignment()),
+                                                 Zero);
   }
   return unknown();
 }
@@ -561,21 +583,6 @@ SizeOffsetType ObjectSizeOffsetVisitor::
   if (!Arg)
     return unknown();
 
-  // When we're compiling N-bit code, and the user uses parameters that are
-  // greater than N bits (e.g. uint64_t on a 32-bit build), we can run into
-  // trouble with APInt size issues. This function handles resizing + overflow
-  // checks for us.
-  auto CheckedZextOrTrunc = [&](APInt &I) {
-    // More bits than we can handle. Checking the bit width isn't necessary, but
-    // it's faster than checking active bits, and should give `false` in the
-    // vast majority of cases.
-    if (I.getBitWidth() > IntTyBits && I.getActiveBits() > IntTyBits)
-      return false;
-    if (I.getBitWidth() != IntTyBits)
-      I = I.zextOrTrunc(IntTyBits);
-    return true;
-  };
-
   APInt Size = Arg->getValue();
   if (!CheckedZextOrTrunc(Size))
     return unknown();