[PATCH] D23354: [compiler-rt] Suport dynamic shadow address instrumentation

[Reid Kleckner via llvm-commits]

rnk added inline comments.

================
Comment at: lib/Transforms/Instrumentation/AddressSanitizer.cpp:445
@@ -437,1 +444,3 @@
+                           && !(Mapping.Offset & (Mapping.Offset - 1))
+                           && Mapping.Offset != ~(uint64_t)0;
 
----------------
Can we make a kDynamicShadowSentinel for this?

================
Comment at: lib/Transforms/Instrumentation/AddressSanitizer.cpp:906
@@ -893,1 +905,3 @@
   // (Shadow >> scale) | offset
+  Value* ShadowBase;
+  if (LocalDynamicShadow)
----------------
LLVM typically uses right leaning pointers and references.

================
Comment at: lib/Transforms/Instrumentation/AddressSanitizer.cpp:1770
@@ +1769,3 @@
+  IRBuilder<> IRB(&F.front().front());
+  LocalDynamicShadow = IRB.CreateAlloca(IntptrTy);
+  assert(LocalDynamicShadow->isStaticAlloca());
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Why create a local alloca and then load from it? This might end up being really slow in -O0 if we reload the shadow base from the stack before every user memory access. If we know we're in the entry block, we should be able to skip the alloca and change this to:
  Value *GlobalDynamicAddress = F.getParent()->getOrInsertGlobal(
      kAsanShadowMemoryDynamicAddress, IntptrTy);
  LocalDynamicShadow = IRB.CreateLoad(GlobalDynamicAddress);

We can then skip the extra load in memToShadow and use LocalDynamicShadow directly.


https://reviews.llvm.org/D23354