[llvm-commits] [llvm] r120485 - in /llvm/trunk: include/llvm/Analysis/ValueTracking.h lib/Transforms/Scalar/DeadStoreElimination.cpp test/Transforms/DeadStoreElimination/PartialStore.ll
Chris Lattner
sabre at nondot.org
Tue Nov 30 15:05:20 PST 2010
Author: lattner
Date: Tue Nov 30 17:05:20 2010
New Revision: 120485
URL: http://llvm.org/viewvc/llvm-project?rev=120485&view=rev
Log:
teach DSE to use GetPointerBaseWithConstantOffset to analyze
may-aliasing stores that partially overlap with different base
pointers. This implements PR6043 and the non-variable part of
PR8657
Modified:
llvm/trunk/include/llvm/Analysis/ValueTracking.h
llvm/trunk/lib/Transforms/Scalar/DeadStoreElimination.cpp
llvm/trunk/test/Transforms/DeadStoreElimination/PartialStore.ll
Modified: llvm/trunk/include/llvm/Analysis/ValueTracking.h
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/Analysis/ValueTracking.h?rev=120485&r1=120484&r2=120485&view=diff
==============================================================================
--- llvm/trunk/include/llvm/Analysis/ValueTracking.h (original)
+++ llvm/trunk/include/llvm/Analysis/ValueTracking.h Tue Nov 30 17:05:20 2010
@@ -102,6 +102,11 @@
/// base and offset to the caller.
Value *GetPointerBaseWithConstantOffset(Value *Ptr, int64_t &Offset,
const TargetData &TD);
+ static inline const Value *
+ GetPointerBaseWithConstantOffset(const Value *Ptr, int64_t &Offset,
+ const TargetData &TD) {
+ return GetPointerBaseWithConstantOffset(const_cast<Value*>(Ptr), Offset,TD);
+ }
/// GetConstantStringInfo - This function computes the length of a
/// null-terminated C string pointed to by V. If successful, it returns true
Modified: llvm/trunk/lib/Transforms/Scalar/DeadStoreElimination.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/DeadStoreElimination.cpp?rev=120485&r1=120484&r2=120485&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Scalar/DeadStoreElimination.cpp (original)
+++ llvm/trunk/lib/Transforms/Scalar/DeadStoreElimination.cpp Tue Nov 30 17:05:20 2010
@@ -28,6 +28,7 @@
#include "llvm/Analysis/Dominators.h"
#include "llvm/Analysis/MemoryBuiltins.h"
#include "llvm/Analysis/MemoryDependenceAnalysis.h"
+#include "llvm/Analysis/ValueTracking.h"
#include "llvm/Target/TargetData.h"
#include "llvm/Transforms/Utils/Local.h"
using namespace llvm;
@@ -260,28 +261,60 @@
static bool isCompleteOverwrite(const AliasAnalysis::Location &Later,
const AliasAnalysis::Location &Earlier,
AliasAnalysis &AA) {
- const Value *P1 = Later.Ptr->stripPointerCasts();
- const Value *P2 = Earlier.Ptr->stripPointerCasts();
+ const Value *P1 = Earlier.Ptr->stripPointerCasts();
+ const Value *P2 = Later.Ptr->stripPointerCasts();
- // Make sure that the start pointers are the same.
- if (P1 != P2)
- return false;
-
- // If we don't know the sizes of either access, then we can't do a comparison.
+ // If the start pointers are the same, we just have to compare sizes to see if
+ // the later store was larger than the earlier store.
+ if (P1 == P2) {
+ // 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 TargetData 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 (AA.getTargetData() == 0)
+ return Later.Ptr->getType() == Earlier.Ptr->getType();
+ return false;
+ }
+
+ // Make sure that the Later size is >= the Earlier size.
+ if (Later.Size < Earlier.Size)
+ return false;
+ return true;
+ }
+
+ // Otherwise, we have to have size information, and the later store has to be
+ // larger than the earlier one.
if (Later.Size == AliasAnalysis::UnknownSize ||
- Earlier.Size == AliasAnalysis::UnknownSize) {
- // If we have no TargetData 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 (AA.getTargetData() == 0)
- return Later.Ptr->getType() == Earlier.Ptr->getType();
+ Earlier.Size == AliasAnalysis::UnknownSize ||
+ Later.Size <= Earlier.Size ||
+ AA.getTargetData() == 0)
return false;
- }
- // Make sure that the Later size is >= the Earlier size.
- if (Later.Size < Earlier.Size)
+ const TargetData &TD = *AA.getTargetData();
+
+ // Okay, we have stores to two completely different pointers. Try to
+ // decompose the pointer into a "base + constant_offset" form. If the base
+ // pointers are equal, then we can reason about the two stores.
+ int64_t Off1 = 0, Off2 = 0;
+ const Value *BP1 = GetPointerBaseWithConstantOffset(P1, Off1, TD);
+ const Value *BP2 = GetPointerBaseWithConstantOffset(P2, Off2, TD);
+
+ // If the base pointers still differ, we have two completely different stores.
+ if (BP1 != BP2)
return false;
+ // Otherwise, we might have a situation like:
+ // store i16 -> P + 1 Byte
+ // store i32 -> P
+ // In this case, we see if the later store completely overlaps all bytes
+ // stored by the previous store.
+ if (Off1 < Off2 || // Earlier starts before Later.
+ Off1+Earlier.Size > Off2+Later.Size) // Earlier goes beyond Later.
+ return false;
+ // Otherwise, we have complete overlap.
return true;
}
Modified: llvm/trunk/test/Transforms/DeadStoreElimination/PartialStore.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/DeadStoreElimination/PartialStore.ll?rev=120485&r1=120484&r2=120485&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/DeadStoreElimination/PartialStore.ll (original)
+++ llvm/trunk/test/Transforms/DeadStoreElimination/PartialStore.ll Tue Nov 30 17:05:20 2010
@@ -36,3 +36,19 @@
%tmp.7 = zext i1 %tmp.6 to i32
ret i32 %tmp.7
}
+
+; PR6043
+define void @test4(i8* %P) {
+; CHECK: @test4
+; CHECK-NEXT: bitcast
+; CHECK-NEXT: store double
+
+ store i8 19, i8* %P ;; dead
+ %A = getelementptr i8* %P, i32 3
+
+ store i8 42, i8* %A ;; dead
+
+ %Q = bitcast i8* %P to double*
+ store double 0.0, double* %Q
+ ret void
+}
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