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ObjC library call with call return. ARC contraction tries to replace uses of an argument passed to an objective-c library call with the call return value. For example, in the following IR, it replaces uses of argument %9 and uses of the values discovered traversing the chain upwards (%7 and %8) with the call return %10, if they are dominated by the call to @objc_autoreleaseReturnValue. This transformation enables code-gen to tail-call the call to @objc_autoreleaseReturnValue, which is necessary to enable auto release return value optimization. %7 = tail call i8* @objc_loadWeakRetained(i8** %6) %8 = bitcast i8* %7 to %0* %9 = bitcast %0* %8 to i8* %10 = tail call i8* @objc_autoreleaseReturnValue(i8* %9) ret %0* %8 Since r276727, llvm started removing redundant bitcasts and as a result started feeding the following IR to ARC contraction: %7 = tail call i8* @objc_loadWeakRetained(i8** %6) %8 = bitcast i8* %7 to %0* %9 = tail call i8* @objc_autoreleaseReturnValue(i8* %7) ret %0* %8 ARC contraction no longer does the optimization described above since it only traverses the chain upwards and fails to recognize that the function return can be replaced by the call return. This commit changes ARC contraction to traverse the chain downwards too and replace uses of bitcasts with the call return. rdar://problem/28011339 Differential Revision: https://reviews.llvm.org/D24523 llvm-svn: 281419
19 lines
557 B
LLVM
19 lines
557 B
LLVM
; RUN: opt -objc-arc-contract -S < %s | FileCheck %s
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declare i8* @objc_autoreleaseReturnValue(i8*)
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declare i8* @foo1()
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; Check that ARC contraction replaces the function return with the value
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; returned by @objc_autoreleaseReturnValue.
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; CHECK: %[[V0:[0-9]+]] = tail call i8* @objc_autoreleaseReturnValue(
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; CHECK: %[[V1:[0-9]+]] = bitcast i8* %[[V0]] to i32*
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; CHECK: ret i32* %[[V1]]
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define i32* @autoreleaseRVTailCall() {
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%1 = call i8* @foo1()
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%2 = bitcast i8* %1 to i32*
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%3 = tail call i8* @objc_autoreleaseReturnValue(i8* %1)
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ret i32* %2
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}
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