[llvm] 639a78a - [MemoryLocation] Support strncpy in getForArgument.

[Florian Hahn via llvm-commits]

Author: Florian Hahn
Date: 2021-12-02T14:18:05Z
New Revision: 639a78a4bf9da0a03dcd12c27f625a134a3ee6cc

URL: https://github.com/llvm/llvm-project/commit/639a78a4bf9da0a03dcd12c27f625a134a3ee6cc
DIFF: https://github.com/llvm/llvm-project/commit/639a78a4bf9da0a03dcd12c27f625a134a3ee6cc.diff

LOG: [MemoryLocation] Support strncpy in getForArgument.

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.

Reviewed By: xbolva00

Differential Revision: https://reviews.llvm.org/D114871

Added: 
    

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

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Analysis/MemoryLocation.cpp b/llvm/lib/Analysis/MemoryLocation.cpp
index b4eb06dec03a..854ba83bd34a 100644
--- a/llvm/lib/Analysis/MemoryLocation.cpp
+++ b/llvm/lib/Analysis/MemoryLocation.cpp
@@ -223,6 +223,18 @@ MemoryLocation MemoryLocation::getForArgument(const CallBase *Call,
       }
       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");

diff  --git a/llvm/test/Analysis/BasicAA/libfuncs.ll b/llvm/test/Analysis/BasicAA/libfuncs.ll
index 476e77bb781d..253a154de501 100644
--- a/llvm/test/Analysis/BasicAA/libfuncs.ll
+++ b/llvm/test/Analysis/BasicAA/libfuncs.ll
@@ -136,9 +136,9 @@ define i8* @test_strncpy_const_size(i8* noalias %a, i8* noalias %b) {
 ; 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)