[PATCH] D65417: [SCCP] Update condition to avoid overflow.

[Alina Sbirlea via Phabricator via llvm-commits]

asbirlea created this revision.
asbirlea added reviewers: sanjoy, RKSimon.
Herald added a subscriber: jlebar.
Herald added a project: LLVM.

Update condition to remove addition that may cause an overflow.
Resolves PR42814.


Repository:
  rL LLVM

https://reviews.llvm.org/D65417

Files:
  lib/Analysis/ConstantFolding.cpp
  test/Transforms/SCCP/ubsan_overflow.ll


Index: test/Transforms/SCCP/ubsan_overflow.ll
===================================================================
--- /dev/null
+++ test/Transforms/SCCP/ubsan_overflow.ll
@@ -0,0 +1,13 @@
+; RUN: opt -sccp -S %s | FileCheck %s
+
+ at 0 = private unnamed_addr constant [16 x i8] c"\01\00\00\00\01\01\00\00\01\01\01\00\01\01\01\01"
+
+; CHECK_LABEL: @foo
+define void @foo() local_unnamed_addr {
+entry:
+  %0 = add nuw nsw i64 0, -1
+  %1 = lshr i64 %0, 1
+  %2 = getelementptr inbounds [4 x [4 x i8]], [4 x [4 x i8]]* bitcast ([16 x i8]* @0 to [4 x [4 x i8]]*), i64 0, i64 0, i64 %1
+  %3 = load i8, i8* %2, align 1
+  unreachable
+}
Index: lib/Analysis/ConstantFolding.cpp
===================================================================
--- lib/Analysis/ConstantFolding.cpp
+++ lib/Analysis/ConstantFolding.cpp
@@ -544,7 +544,7 @@
   int64_t InitializerSize = DL.getTypeAllocSize(GV->getInitializer()->getType());
 
   // If we're not accessing anything in this constant, the result is undefined.
-  if (Offset + BytesLoaded <= 0)
+  if (Offset <= -BytesLoaded)
     return UndefValue::get(IntType);
 
   // If we're not accessing anything in this constant, the result is undefined.


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