[PATCH] D114871: [MemoryLocation] Support strncpy in getForArgument.

[Florian Hahn via Phabricator via llvm-commits]

fhahn created this revision.
fhahn added reviewers: fwolff, xbolva00, efriedma, jdoerfert.
Herald added a subscriber: hiraditya.
fhahn requested review of this revision.
Herald added a project: LLVM.

The size argument of strncpy can be used as bound for the size of
its pointer arguments.

strncpy is guaranteed to write N bytes and reads up to N bytes.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D114871

Files:
  llvm/lib/Analysis/MemoryLocation.cpp
  llvm/test/Analysis/BasicAA/libfuncs.ll


Index: llvm/test/Analysis/BasicAA/libfuncs.ll
===================================================================
--- llvm/test/Analysis/BasicAA/libfuncs.ll
+++ llvm/test/Analysis/BasicAA/libfuncs.ll
@@ -136,9 +136,9 @@
 ; CHECK-NEXT:  Just Ref:  Ptr: i8* %b	<->  %res = tail call i8* @strncpy(i8* %a, i8* %b, i64 4)
 ; CHECK-NEXT:  Just Mod:  Ptr: i8* %res	<->  %res = tail call i8* @strncpy(i8* %a, i8* %b, i64 4)
 ; CHECK-NEXT:  Just Mod:  Ptr: i8* %a.gep.1	<->  %res = tail call i8* @strncpy(i8* %a, i8* %b, i64 4)
-; CHECK-NEXT:  Just Mod:  Ptr: i8* %a.gep.5	<->  %res = tail call i8* @strncpy(i8* %a, i8* %b, i64 4)
+; CHECK-NEXT:  NoModRef:  Ptr: i8* %a.gep.5	<->  %res = tail call i8* @strncpy(i8* %a, i8* %b, i64 4)
 ; CHECK-NEXT:  Just Ref:  Ptr: i8* %b.gep.1	<->  %res = tail call i8* @strncpy(i8* %a, i8* %b, i64 4)
-; CHECK-NEXT:  Just Ref:  Ptr: i8* %b.gep.5	<->  %res = tail call i8* @strncpy(i8* %a, i8* %b, i64 4)
+; CHECK-NEXT:  NoModRef:  Ptr: i8* %b.gep.5	<->  %res = tail call i8* @strncpy(i8* %a, i8* %b, i64 4)
 ;
 entry:
   %res = tail call i8* @strncpy(i8* %a, i8* %b, i64 4)
Index: llvm/lib/Analysis/MemoryLocation.cpp
===================================================================
--- llvm/lib/Analysis/MemoryLocation.cpp
+++ llvm/lib/Analysis/MemoryLocation.cpp
@@ -223,6 +223,18 @@
       }
       return MemoryLocation(Arg, Size, AATags);
     }
+    case LibFunc_strncpy: {
+      assert((ArgIdx == 0 || ArgIdx == 1) &&
+             "Invalid argument index for strncpy");
+      LocationSize Size = LocationSize::afterPointer();
+      if (const auto *Len = dyn_cast<ConstantInt>(Call->getArgOperand(2))) {
+        // strncpy is guaranteed to write Len bytes, but only reads up to Len
+        // bytes.
+        Size = ArgIdx == 0 ? LocationSize::precise(Len->getZExtValue())
+                           : LocationSize::upperBound(Len->getZExtValue());
+      }
+      return MemoryLocation(Arg, Size, AATags);
+    }
     case LibFunc_memset_pattern16:
       assert((ArgIdx == 0 || ArgIdx == 1) &&
              "Invalid argument index for memset_pattern16");


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