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implement constant folding support for an exotic constant expr:

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ret i64 ptrtoint (i8* getelementptr ([1000 x i8]* @X, i64 1, i64 sub (i64 0, i64 ptrtoint ([1000 x i8]* @X to i64))) to i64)

to "ret i64 1000".  This allows us to correctly compute the trip count
on a loop in PR8883, which occurs with std::fill on a char array.  This
allows us to transform it into a memset with a constant size.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@122950 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner
2011-01-06 06:19:46 +00:00
parent 255874ff52
commit 8cd4efb6a5
2 changed files with 38 additions and 1 deletions
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19
test/Transforms/InstCombine/constant-fold-gep.ll
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@@ -53,3 +53,22 @@ define void @frob() {
store i32 1, i32* getelementptr ([3 x %struct.X]* @Y, i64 0, i64 0, i32 0, i64 19), align 8
ret void
}
; PR8883 - Constant fold exotic gep subtract
; CHECK: @test2
@X = global [1000 x i8] zeroinitializer, align 16
define i64 @test2() {
entry:
%A = bitcast i8* getelementptr inbounds ([1000 x i8]* @X, i64 1, i64 0) to i8*
%B = bitcast i8* getelementptr inbounds ([1000 x i8]* @X, i64 0, i64 0) to i8*
%B2 = ptrtoint i8* %B to i64
%C = sub i64 0, %B2
%D = getelementptr i8* %A, i64 %C
%E = ptrtoint i8* %D to i64
ret i64 %E
; CHECK: ret i64 1000
}