77eeac3d9e
Summary: Support for this option is needed for building Linux kernel. This is a very frequently requested feature by kernel developers. More details : https://lkml.org/lkml/2018/4/4/601 GCC option description for -fdelete-null-pointer-checks: This Assume that programs cannot safely dereference null pointers, and that no code or data element resides at address zero. -fno-delete-null-pointer-checks is the inverse of this implying that null pointer dereferencing is not undefined. This feature is implemented in LLVM IR in this CL as the function attribute "null-pointer-is-valid"="true" in IR (Under review at D47894). The CL updates several passes that assumed null pointer dereferencing is undefined to not optimize when the "null-pointer-is-valid"="true" attribute is present. Reviewers: t.p.northover, efriedma, jyknight, chandlerc, rnk, srhines, void, george.burgess.iv Reviewed By: efriedma, george.burgess.iv Subscribers: eraman, haicheng, george.burgess.iv, drinkcat, theraven, reames, sanjoy, xbolva00, llvm-commits Differential Revision: https://reviews.llvm.org/D47895 llvm-svn: 336613
33 lines
969 B
LLVM
33 lines
969 B
LLVM
; RUN: opt < %s -globalopt -S | FileCheck %s
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target datalayout = "E-p:64:64:64-a0:0:8-f32:32:32-f64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:32:64-v64:64:64-v128:128:128"
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@G = internal global i32* null ; <i32**> [#uses=4]
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; CHECK-NOT: global
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define void @init() {
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%malloccall = tail call i8* @malloc(i64 4) ; <i8*> [#uses=1]
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%P = bitcast i8* %malloccall to i32* ; <i32*> [#uses=1]
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store i32* %P, i32** @G
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%GV = load i32*, i32** @G ; <i32*> [#uses=1]
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store i32 0, i32* %GV
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ret void
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}
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declare noalias i8* @malloc(i64)
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define i32 @get() {
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%GV = load i32*, i32** @G ; <i32*> [#uses=1]
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%V = load i32, i32* %GV ; <i32> [#uses=1]
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ret i32 %V
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; CHECK: ret i32 0
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}
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define void @foo(i64 %Size) nounwind noinline #0 {
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entry:
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%0 = load i32*, i32** @G, align 4
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ret void
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}
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attributes #0 = { "null-pointer-is-valid"="true" }
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