[FIX] Handle accesses to "null" in MemIntrinsics

This fixes PR27035. While we now exclude MemIntrinsics from the
  polyhedral model if they would access "null" we could exploit this
  even more, e.g., remove all parameter combinations that would lead to
  the execution of this statement from the context.

llvm-svn: 264284

polly/lib/Analysis/ScopDetection.cpp

@@ -533,17 +533,21 @@ bool ScopDetection::isValidIntrinsicInst(IntrinsicInst &II,
   case llvm::Intrinsic::memmove:
   case llvm::Intrinsic::memcpy:
     AF = SE->getSCEVAtScope(cast<MemTransferInst>(II).getSource(), L);
-    BP = dyn_cast<SCEVUnknown>(SE->getPointerBase(AF));
-    // Bail if the source pointer is not valid.
-    if (!isValidAccess(&II, AF, BP, Context))
-      return false;
+    if (!AF->isZero()) {
+      BP = dyn_cast<SCEVUnknown>(SE->getPointerBase(AF));
+      // Bail if the source pointer is not valid.
+      if (!isValidAccess(&II, AF, BP, Context))
+        return false;
+    }
   // Fall through
   case llvm::Intrinsic::memset:
     AF = SE->getSCEVAtScope(cast<MemIntrinsic>(II).getDest(), L);
-    BP = dyn_cast<SCEVUnknown>(SE->getPointerBase(AF));
-    // Bail if the destination pointer is not valid.
-    if (!isValidAccess(&II, AF, BP, Context))
-      return false;
+    if (!AF->isZero()) {
+      BP = dyn_cast<SCEVUnknown>(SE->getPointerBase(AF));
+      // Bail if the destination pointer is not valid.
+      if (!isValidAccess(&II, AF, BP, Context))
+        return false;
+    }
 
     // Bail if the length is not affine.
     if (!isAffine(SE->getSCEVAtScope(cast<MemIntrinsic>(II).getLength(), L), L,

polly/lib/Analysis/ScopInfo.cpp

@@ -3942,8 +3942,17 @@ bool ScopInfo::buildAccessMemIntrinsic(
 
   auto *DestPtrVal = MemIntr->getDest();
   assert(DestPtrVal);
+
   auto *DestAccFunc = SE->getSCEVAtScope(DestPtrVal, L);
   assert(DestAccFunc);
+  // Ignore accesses to "NULL".
+  // TODO: We could use this to optimize the region further, e.g., intersect
+  //       the context with
+  //          isl_set_complement(isl_set_params(getDomain()))
+  //       as we know it would be undefined to execute this instruction anyway.
+  if (DestAccFunc->isZero())
+    return true;
+
   auto *DestPtrSCEV = dyn_cast<SCEVUnknown>(SE->getPointerBase(DestAccFunc));
   assert(DestPtrSCEV);
   DestAccFunc = SE->getMinusSCEV(DestAccFunc, DestPtrSCEV);
@@ -3957,8 +3966,14 @@ bool ScopInfo::buildAccessMemIntrinsic(
 
   auto *SrcPtrVal = MemTrans->getSource();
   assert(SrcPtrVal);
+
   auto *SrcAccFunc = SE->getSCEVAtScope(SrcPtrVal, L);
   assert(SrcAccFunc);
+  // Ignore accesses to "NULL".
+  // TODO: See above TODO
+  if (SrcAccFunc->isZero())
+    return true;
+
   auto *SrcPtrSCEV = dyn_cast<SCEVUnknown>(SE->getPointerBase(SrcAccFunc));
   assert(SrcPtrSCEV);
   SrcAccFunc = SE->getMinusSCEV(SrcAccFunc, SrcPtrSCEV);

polly/test/ScopInfo/memset_null.ll

@@ -0,0 +1,37 @@
+; RUN: opt %loadPolly -polly-allow-modref-calls -polly-scops -analyze < %s | FileCheck %s
+; RUN: opt %loadPolly -polly-allow-modref-calls -S -polly-codegen < %s
+;
+; Verify we can handle a memset to "null" and that we do not model it.
+; TODO: FIXME: We could use the undefined memset to optimize the code further,
+;              see the TODOs in the ScopInfo.cpp.
+;
+; CHECK:         Statements {
+; CHECK-NEXT:        Stmt_for_cond5_preheader_us221
+; CHECK-NEXT:            Domain :=
+; CHECK-NEXT:                { Stmt_for_cond5_preheader_us221[0] };
+; CHECK-NEXT:            Schedule :=
+; CHECK-NEXT:                { Stmt_for_cond5_preheader_us221[i0] -> [0] };
+; CHECK-NEXT:            MustWriteAccess :=	[Reduction Type: NONE] [Scalar: 0]
+; CHECK-NEXT:                { Stmt_for_cond5_preheader_us221[i0] -> MemRef_A[0] };
+; CHECK-NEXT:    }
+
+;
+target datalayout = "e-m:e-i64:64-i128:128-n8:16:32:64-S128"
+
+define void @test(i32* %A) {
+entry:
+  br i1 undef, label %for.end68, label %for.cond5.preheader.lr.ph
+
+for.cond5.preheader.lr.ph:                        ; preds = %entry
+  br label %for.cond5.preheader.us221
+
+for.cond5.preheader.us221:                        ; preds = %for.cond5.preheader.us221, %for.cond5.preheader.lr.ph
+  store i32 0, i32* %A
+  call void @llvm.memset.p0i8.i64(i8* null, i8 0, i64 undef, i32 1, i1 false)
+  br i1 true, label %for.end68, label %for.cond5.preheader.us221
+
+for.end68:                                        ; preds = %for.cond5.preheader.us221, %entry
+  ret void
+}
+
+declare void @llvm.memset.p0i8.i64(i8* nocapture, i8, i64, i32, i1)