[IR] Add overflow check in AllocaInst::getAllocationSize

[tszhin-swe]

Fixes #91380

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[llvmbot]

@llvm/pr-subscribers-llvm-ir

Author: Tsz Chan (tszhin-swe)

Changes

---

Full diff: https://github.com/llvm/llvm-project/pull/97170.diff

2 Files Affected:

• (modified) llvm/lib/IR/Instructions.cpp (+22-10)
• (modified) llvm/unittests/IR/InstructionsTest.cpp (+3)

diff --git a/llvm/lib/IR/Instructions.cpp b/llvm/lib/IR/Instructions.cpp
index 494306815d90d..0b926c8595297 100644
--- a/llvm/lib/IR/Instructions.cpp
+++ b/llvm/lib/IR/Instructions.cpp
@@ -37,6 +37,7 @@
 #include "llvm/IR/Value.h"
 #include "llvm/Support/AtomicOrdering.h"
 #include "llvm/Support/Casting.h"
+#include "llvm/Support/CheckedArithmetic.h"
 #include "llvm/Support/ErrorHandling.h"
 #include "llvm/Support/MathExtras.h"
 #include "llvm/Support/ModRef.h"
@@ -60,22 +61,33 @@ static cl::opt<bool> DisableI2pP2iOpt(
 std::optional<TypeSize>
 AllocaInst::getAllocationSize(const DataLayout &DL) const {
   TypeSize Size = DL.getTypeAllocSize(getAllocatedType());
-  if (isArrayAllocation()) {
-    auto *C = dyn_cast<ConstantInt>(getArraySize());
-    if (!C)
-      return std::nullopt;
-    assert(!Size.isScalable() && "Array elements cannot have a scalable size");
-    Size *= C->getZExtValue();
+  if (!isArrayAllocation()) {
+    return Size;
   }
-  return Size;
+  auto *C = dyn_cast<ConstantInt>(getArraySize());
+  if (!C)
+    return std::nullopt;
+  assert(!Size.isScalable() && "Array elements cannot have a scalable size");
+  auto checkedProd =
+      checkedMulUnsigned(Size.getKnownMinValue(), C->getZExtValue());
+  if (!checkedProd) {
+    return std::nullopt;
+  }
+  return TypeSize::getFixed(*checkedProd);
 }
 
 std::optional<TypeSize>
 AllocaInst::getAllocationSizeInBits(const DataLayout &DL) const {
   std::optional<TypeSize> Size = getAllocationSize(DL);
-  if (Size)
-    return *Size * 8;
-  return std::nullopt;
+  if (!Size) {
+    return std::nullopt;
+  }
+  auto CheckedProd = checkedMulUnsigned((*Size).getKnownMinValue(),
+                                        static_cast<TypeSize::ScalarTy>(8));
+  if (!CheckedProd) {
+    return std::nullopt;
+  }
+  return TypeSize::get(*CheckedProd, (*Size).isScalable());
 }
 
 //===----------------------------------------------------------------------===//
diff --git a/llvm/unittests/IR/InstructionsTest.cpp b/llvm/unittests/IR/InstructionsTest.cpp
index b6044b2862920..4c1e9a9acb29a 100644
--- a/llvm/unittests/IR/InstructionsTest.cpp
+++ b/llvm/unittests/IR/InstructionsTest.cpp
@@ -1750,6 +1750,7 @@ TEST(InstructionsTest, AllocaInst) {
         %F = alloca [2 x half]
         %G = alloca [2 x [3 x i128]]
         %H = alloca %T
+        %I = alloca i32, i64 9223372036854775807
         ret void
       }
     )");
@@ -1766,6 +1767,7 @@ TEST(InstructionsTest, AllocaInst) {
   AllocaInst &F = cast<AllocaInst>(*It++);
   AllocaInst &G = cast<AllocaInst>(*It++);
   AllocaInst &H = cast<AllocaInst>(*It++);
+  AllocaInst &I = cast<AllocaInst>(*It++);
   EXPECT_EQ(A.getAllocationSizeInBits(DL), TypeSize::getFixed(32));
   EXPECT_EQ(B.getAllocationSizeInBits(DL), TypeSize::getFixed(128));
   EXPECT_FALSE(C.getAllocationSizeInBits(DL));
@@ -1774,6 +1776,7 @@ TEST(InstructionsTest, AllocaInst) {
   EXPECT_EQ(F.getAllocationSizeInBits(DL), TypeSize::getFixed(32));
   EXPECT_EQ(G.getAllocationSizeInBits(DL), TypeSize::getFixed(768));
   EXPECT_EQ(H.getAllocationSizeInBits(DL), TypeSize::getFixed(160));
+  EXPECT_FALSE(I.getAllocationSizeInBits(DL));
 }
 
 TEST(InstructionsTest, InsertAtBegin) {

[nikic]

LGTM

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