[llvm] r220035 - [DSE] Remove no-data-layout-only type-based overlap checking

[Hal Finkel]

Author: hfinkel
Date: Fri Oct 17 06:56:00 2014
New Revision: 220035

URL: http://llvm.org/viewvc/llvm-project?rev=220035&view=rev
Log:
[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.

Modified:
    llvm/trunk/lib/Transforms/Scalar/DeadStoreElimination.cpp
    llvm/trunk/test/Analysis/TypeBasedAliasAnalysis/dse.ll
    llvm/trunk/test/Transforms/DeadStoreElimination/const-pointers.ll
    llvm/trunk/test/Transforms/DeadStoreElimination/inst-limits.ll
    llvm/trunk/test/Transforms/DeadStoreElimination/no-targetdata.ll

Modified: llvm/trunk/lib/Transforms/Scalar/DeadStoreElimination.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/DeadStoreElimination.cpp?rev=220035&r1=220034&r2=220035&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Scalar/DeadStoreElimination.cpp (original)
+++ llvm/trunk/lib/Transforms/Scalar/DeadStoreElimination.cpp Fri Oct 17 06:56:00 2014
@@ -356,15 +356,8 @@ static OverwriteResult isOverwrite(const
     // 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)

Modified: llvm/trunk/test/Analysis/TypeBasedAliasAnalysis/dse.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Analysis/TypeBasedAliasAnalysis/dse.ll?rev=220035&r1=220034&r2=220035&view=diff
==============================================================================
--- llvm/trunk/test/Analysis/TypeBasedAliasAnalysis/dse.ll (original)
+++ llvm/trunk/test/Analysis/TypeBasedAliasAnalysis/dse.ll Fri Oct 17 06:56:00 2014
@@ -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.
 

Modified: llvm/trunk/test/Transforms/DeadStoreElimination/const-pointers.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/DeadStoreElimination/const-pointers.ll?rev=220035&r1=220034&r2=220035&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/DeadStoreElimination/const-pointers.ll (original)
+++ llvm/trunk/test/Transforms/DeadStoreElimination/const-pointers.ll Fri Oct 17 06:56:00 2014
@@ -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 }
 

Modified: llvm/trunk/test/Transforms/DeadStoreElimination/inst-limits.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/DeadStoreElimination/inst-limits.ll?rev=220035&r1=220034&r2=220035&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/DeadStoreElimination/inst-limits.ll (original)
+++ llvm/trunk/test/Transforms/DeadStoreElimination/inst-limits.ll Fri Oct 17 06:56:00 2014
@@ -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

Modified: llvm/trunk/test/Transforms/DeadStoreElimination/no-targetdata.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/DeadStoreElimination/no-targetdata.ll?rev=220035&r1=220034&r2=220035&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/DeadStoreElimination/no-targetdata.ll (original)
+++ llvm/trunk/test/Transforms/DeadStoreElimination/no-targetdata.ll Fri Oct 17 06:56:00 2014
@@ -1,15 +1,21 @@
 ; RUN: opt -basicaa -dse -S < %s | FileCheck %s
 
-declare void @test1f()
+declare void @llvm.memcpy.p0i8.p0i8.i64(i8* nocapture, i8* nocapture, i64, i32, i1) nounwind
 
-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
+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
 }
+