[DSE] Remove no-data-layout-only type-based overlap checking

DSE's overlap checking contained special logic, used only when no DataLayout
was available, which inferred a complete overwrite when the pointee types were
equal. This logic seems fine for regular loads/stores, but does not work for
memcpy and friends. Instead of fixing this, I'm just removing it.
Philosophically, transformations should not contain enhanced behavior used only
when data layout is lacking (data layout should be strictly additive), and
maintaining these rarely-tested code paths seems not worthwhile at this stage.

Credit to Aliaksei Zasenka for the bug report and the diagnosis. The test case
(slightly reduced from that provided by Aliaksei) replaces the original
contents of test/Transforms/DeadStoreElimination/no-targetdata.ll -- a few
other tests have been updated to have a data layout.

llvm-svn: 220035

diff --git a/llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp b/llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp
index 3af8ee7..a1ddc00 100644 (file)
--- a/llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp
+++ b/llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp
@@ -356,15 +356,8 @@ static OverwriteResult isOverwrite(const AliasAnalysis::Location &Later,
     // If we don't know the sizes of either access, then we can't do a
     // comparison.
     if (Later.Size == AliasAnalysis::UnknownSize ||
-        Earlier.Size == AliasAnalysis::UnknownSize) {
-      // If we have no DataLayout information around, then the size of the store
-      // is inferrable from the pointee type.  If they are the same type, then
-      // we know that the store is safe.
-      if (DL == nullptr && Later.Ptr->getType() == Earlier.Ptr->getType())
-        return OverwriteComplete;
-
+        Earlier.Size == AliasAnalysis::UnknownSize)
       return OverwriteUnknown;
-    }
 
     // Make sure that the Later size is >= the Earlier size.
     if (Later.Size >= Earlier.Size)

diff --git a/llvm/test/Analysis/TypeBasedAliasAnalysis/dse.ll b/llvm/test/Analysis/TypeBasedAliasAnalysis/dse.ll
index bcf1f2c..9032fad 100644 (file)
--- a/llvm/test/Analysis/TypeBasedAliasAnalysis/dse.ll
+++ b/llvm/test/Analysis/TypeBasedAliasAnalysis/dse.ll
@@ -1,4 +1,5 @@
 ; RUN: opt < %s -tbaa -basicaa -dse -S | FileCheck %s
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
 
 ; DSE should make use of TBAA.
 

diff --git a/llvm/test/Transforms/DeadStoreElimination/const-pointers.ll b/llvm/test/Transforms/DeadStoreElimination/const-pointers.ll
index c90d824..3e772d7 100644 (file)
--- a/llvm/test/Transforms/DeadStoreElimination/const-pointers.ll
+++ b/llvm/test/Transforms/DeadStoreElimination/const-pointers.ll
@@ -1,4 +1,5 @@
 ; RUN: opt -basicaa -dse -S < %s | FileCheck %s
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
 
 %t = type { i32 }
 

diff --git a/llvm/test/Transforms/DeadStoreElimination/inst-limits.ll b/llvm/test/Transforms/DeadStoreElimination/inst-limits.ll
index c6e527e..3d78bb5 100644 (file)
--- a/llvm/test/Transforms/DeadStoreElimination/inst-limits.ll
+++ b/llvm/test/Transforms/DeadStoreElimination/inst-limits.ll
@@ -1,4 +1,5 @@
 ; RUN: opt -S -dse < %s | FileCheck %s
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
 
 ; If there are two stores to the same location, DSE should be able to remove
 ; the first store if the two stores are separated by no more than 98

diff --git a/llvm/test/Transforms/DeadStoreElimination/no-targetdata.ll b/llvm/test/Transforms/DeadStoreElimination/no-targetdata.ll
index c0c7c58..2539533 100644 (file)
--- a/llvm/test/Transforms/DeadStoreElimination/no-targetdata.ll
+++ b/llvm/test/Transforms/DeadStoreElimination/no-targetdata.ll
@@ -1,15 +1,21 @@
 ; RUN: opt -basicaa -dse -S < %s | FileCheck %s
 
-declare void @test1f()
-
-define void @test1(i32* noalias %p) {
-       store i32 1, i32* %p
-       call void @test1f()
-       store i32 2, i32 *%p
-       ret void
-; CHECK-LABEL: define void @test1(
-; CHECK-NOT: store
-; CHECK-NEXT: call void
-; CHECK-NEXT: store i32 2
-; CHECK-NEXT: ret void
+declare void @llvm.memcpy.p0i8.p0i8.i64(i8* nocapture, i8* nocapture, i64, i32, i1) nounwind
+
+define void @fn(i8* nocapture %buf) #0 {
+entry:
+
+; We would not eliminate the first memcpy with data layout, and we should not
+; eliminate it without data layout.
+; CHECK-LABEL: @fn
+; CHECK: tail call void @llvm.memcpy.p0i8.p0i8.i64
+; CHECK: tail call void @llvm.memcpy.p0i8.p0i8.i64
+; CHECK: ret void
+
+  %arrayidx = getelementptr i8* %buf, i64 18
+  tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %arrayidx, i8* %buf, i64 18, i32 1, i1 false)
+  store i8 1, i8* %arrayidx, align 1
+  tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %buf, i8* %arrayidx, i64 18, i32 1, i1 false)
+  ret void
 }
+