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fix an issue in IsPointerOffset that prevented us from recognizing that 

P and P+1 are relative to the same base pointer.

llvm-svn: 123087
This commit is contained in:
Chris Lattner 2011-01-08 21:07:56 +00:00
parent 4dc1fd938f
commit 5120ebf184
2 changed files with 31 additions and 3 deletions
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22
llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp
View File

@ -71,13 +71,30 @@ static int64_t GetOffsetFromIndex(const GetElementPtrInst *GEP, unsigned Idx,
/// be &A[42], and Ptr2 might be &A[40]. In this case offset would be -8.
static bool IsPointerOffset(Value *Ptr1, Value *Ptr2, int64_t &Offset,
const TargetData &TD) {
Ptr1 = Ptr1->stripPointerCasts();
Ptr2 = Ptr2->stripPointerCasts();
GetElementPtrInst *GEP1 = dyn_cast<GetElementPtrInst>(Ptr1);
GetElementPtrInst *GEP2 = dyn_cast<GetElementPtrInst>(Ptr2);
bool VariableIdxFound = false;
// If one pointer is a GEP and the other isn't, then see if the GEP is a
// constant offset from the base, as in "P" and "gep P, 1".
if (GEP1 && GEP2 == 0 && GEP1->getOperand(0)->stripPointerCasts() == Ptr2) {
Offset = -GetOffsetFromIndex(GEP1, 1, VariableIdxFound, TD);
return !VariableIdxFound;
}
if (GEP2 && GEP1 == 0 && GEP2->getOperand(0)->stripPointerCasts() == Ptr1) {
Offset = GetOffsetFromIndex(GEP2, 1, VariableIdxFound, TD);
return !VariableIdxFound;
}
// Right now we handle the case when Ptr1/Ptr2 are both GEPs with an identical
// base. After that base, they may have some number of common (and
// potentially variable) indices. After that they handle some constant
// offset, which determines their offset from each other. At this point, we
// handle no other case.
GetElementPtrInst *GEP1 = dyn_cast<GetElementPtrInst>(Ptr1);
GetElementPtrInst *GEP2 = dyn_cast<GetElementPtrInst>(Ptr2);
if (!GEP1 || !GEP2 || GEP1->getOperand(0) != GEP2->getOperand(0))
return false;
@ -87,7 +104,6 @@ static bool IsPointerOffset(Value *Ptr1, Value *Ptr2, int64_t &Offset,
if (GEP1->getOperand(Idx) != GEP2->getOperand(Idx))
break;
bool VariableIdxFound = false;
int64_t Offset1 = GetOffsetFromIndex(GEP1, Idx, VariableIdxFound, TD);
int64_t Offset2 = GetOffsetFromIndex(GEP2, Idx, VariableIdxFound, TD);
if (VariableIdxFound) return false;

12
llvm/test/Transforms/MemCpyOpt/form-memset.ll
View File

@ -177,6 +177,18 @@ entry:
; CHECK: call void @llvm.memset.p0i8.i64(i8* %1, i8 0, i64 15, i32 4, i1 false)
}
define void @test4(i32* nocapture %P) nounwind ssp {
entry:
store i32 0, i32* %P, align 4
%add.ptr = getelementptr inbounds i32* %P, i64 1
%0 = bitcast i32* %add.ptr to i8*
tail call void @llvm.memset.p0i8.i64(i8* %0, i8 0, i64 11, i32 1, i1 false)
ret void
; CHECK: @test4
; CHECK-NOT: store
; CHECK: call void @llvm.memset.p0i8.i64(i8* %1, i8 0, i64 15, i32 4, i1 false)
}
declare void @llvm.memset.p0i8.i64(i8* nocapture, i8, i64, i32, i1) nounwind