Revert "[scudo] Apply filling when realloc shrinks and re-grows a block in-place (llvm#93212)"

This reverts commit 760d880.

It broke https://lab.llvm.org/buildbot/#/builders/169/builds/32309

Author: fabio-d

compiler-rt/lib/scudo/standalone/combined.h

@@ -565,20 +565,6 @@ class Allocator {
             storeSecondaryAllocationStackMaybe(Options, OldPtr, NewSize);
           }
         }
-
-        // If we have reduced the size, set the extra bytes to the fill value
-        // so that we are ready to grow it again in the future.
-        if (NewSize < OldSize) {
-          const FillContentsMode FillContents =
-              TSDRegistry.getDisableMemInit() ? NoFill
-                                              : Options.getFillContentsMode();
-          if (FillContents != NoFill) {
-            memset(reinterpret_cast<char *>(OldTaggedPtr) + NewSize,
-                   FillContents == ZeroFill ? 0 : PatternFillByte,
-                   OldSize - NewSize);
-          }
-        }
-
         return OldTaggedPtr;
       }
     }

compiler-rt/lib/scudo/standalone/tests/combined_test.cpp

@@ -447,32 +447,19 @@ SCUDO_TYPED_TEST(ScudoCombinedDeathTest, ReallocateSame) {
   // returns the same chunk. This requires that all the sizes we iterate on use
   // the same block size, but that should be the case for MaxSize - 64 with our
   // default class size maps.
-  constexpr scudo::uptr InitialSize =
+  constexpr scudo::uptr ReallocSize =
       TypeParam::Primary::SizeClassMap::MaxSize - 64;
+  void *P = Allocator->allocate(ReallocSize, Origin);
   const char Marker = 'A';
-  Allocator->setFillContents(scudo::PatternOrZeroFill);
-
-  void *P = Allocator->allocate(InitialSize, Origin);
-  scudo::uptr CurrentSize = InitialSize;
+  memset(P, Marker, ReallocSize);
   for (scudo::sptr Delta = -32; Delta < 32; Delta += 8) {
-    memset(P, Marker, CurrentSize);
     const scudo::uptr NewSize =
-        static_cast<scudo::uptr>(static_cast<scudo::sptr>(InitialSize) + Delta);
+        static_cast<scudo::uptr>(static_cast<scudo::sptr>(ReallocSize) + Delta);
     void *NewP = Allocator->reallocate(P, NewSize);
     EXPECT_EQ(NewP, P);
-
-    // Verify that existing contents have been preserved.
-    for (scudo::uptr I = 0; I < scudo::Min(CurrentSize, NewSize); I++)
+    for (scudo::uptr I = 0; I < ReallocSize - 32; I++)
       EXPECT_EQ((reinterpret_cast<char *>(NewP))[I], Marker);
-
-    // Verify that new bytes are set according to FillContentsMode.
-    for (scudo::uptr I = CurrentSize; I < NewSize; I++) {
-      EXPECT_EQ((reinterpret_cast<unsigned char *>(NewP))[I],
-                scudo::PatternFillByte);
-    }
-
     checkMemoryTaggingMaybe(Allocator, NewP, NewSize, 0);
-    CurrentSize = NewSize;
   }
   Allocator->deallocate(P, Origin);
 }