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allow eliminating an alloca that is just copied from an constant global

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if it is passed as a byval argument.  The byval argument will just be a
read, so it is safe to read from the original global instead.  This allows
us to promote away the %agg.tmp alloca in PR8582


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@119686 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2010-11-18 06:41:51 +00:00
parent a9be1df6d7
commit 6248065194
2 changed files with 23 additions and 3 deletions
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13
lib/Transforms/Scalar/ScalarReplAggregates.cpp
View File

@ -1811,11 +1811,18 @@ static bool isOnlyCopiedFromConstantGlobal(Value *V, MemTransferInst *&TheCopy,
continue;
}
// If this is a readonly/readnone call site, then we know it is just a load
// and we can ignore it.
if (CallSite CS = U)
if (CallSite CS = U) {
// If this is a readonly/readnone call site, then we know it is just a
// load and we can ignore it.
if (CS.onlyReadsMemory())
continue;
// If this is being passed as a byval argument, the caller is making a
// copy, so it is only a read of the alloca.
unsigned ArgNo = CS.getArgumentNo(UI);
if (CS.paramHasAttr(ArgNo+1, Attribute::ByVal))
continue;
}
// If this is isn't our memcpy/memmove, reject it as something we can't
// handle.

13
test/Transforms/ScalarRepl/memcpy-from-global.ll
View File

@ -81,3 +81,16 @@ define void @test3() {
; CHECK-NEXT: call void @bar(i8* %a)
ret void
}
define void @test4() {
%A = alloca %T
%a = bitcast %T* %A to i8*
call void @llvm.memcpy.p0i8.p0i8.i64(i8* %a, i8* bitcast (%T* @G to i8*), i64 124, i32 4, i1 false)
call void @baz(i8* byval %a)
; CHECK: @test4
; CHECK-NEXT: %a = bitcast %T* @G to i8*
; CHECK-NEXT: call void @baz(i8* byval %a)
ret void
}
declare void @baz(i8* byval)