[PATCH] isDereferenceablePointer: look through gc.relocate calls

[Ramkumar Ramachandra]

Hi reames,

A pointer dereferenceable before a gc.relocate should be dereferenceable
after a gc.relocate, because the gc might not kick in, making the
gc.relocate a noop in some cases (and hence the invariant should hold in
all cases).

http://reviews.llvm.org/D7454

Files:
  lib/IR/Value.cpp
  test/Analysis/ValueTracking/memory-dereferenceable.ll

Index: lib/IR/Value.cpp
===================================================================
--- lib/IR/Value.cpp
+++ lib/IR/Value.cpp
@@ -23,8 +23,10 @@
 #include "llvm/IR/GetElementPtrTypeIterator.h"
 #include "llvm/IR/InstrTypes.h"
 #include "llvm/IR/Instructions.h"
+#include "llvm/IR/IntrinsicInst.h"
 #include "llvm/IR/Module.h"
 #include "llvm/IR/Operator.h"
+#include "llvm/IR/Statepoint.h"
 #include "llvm/IR/ValueHandle.h"
 #include "llvm/IR/ValueSymbolTable.h"
 #include "llvm/Support/Debug.h"
@@ -570,6 +572,13 @@
     return true;
   }
 
+  // For gc.relocate, look through relocations
+  if (const IntrinsicInst *I = dyn_cast<IntrinsicInst>(V))
+    if (I->getIntrinsicID() == Intrinsic::experimental_gc_relocate) {
+      GCRelocateOperands RelocateInst(I);
+      return isDereferenceablePointer(RelocateInst.derivedPtr(), DL, Visited);
+    }
+
   if (const AddrSpaceCastInst *ASC = dyn_cast<AddrSpaceCastInst>(V))
     return isDereferenceablePointer(ASC->getOperand(0), DL, Visited);
 
Index: test/Analysis/ValueTracking/memory-dereferenceable.ll
===================================================================
--- test/Analysis/ValueTracking/memory-dereferenceable.ll
+++ test/Analysis/ValueTracking/memory-dereferenceable.ll
@@ -12,8 +12,7 @@
 ; CHECK: %globalptr
 ; CHECK: %alloca
 ; CHECK: %dparam
-; We haven't yet taught it to look through relocations
-; CHECK-NOT: %relocate
+; CHECK: %relocate
 ; CHECK-NOT: %nparam
 entry:
     %globalptr = getelementptr inbounds [6 x i8]* @globalstr, i32 0, i32 0

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