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[FunctionAttrs] Fix an iterator wraparound bug
Summary: This change fixes an iterator wraparound bug in `determinePointerReadAttrs`. Ideally, ++'ing off the `end()` of an iplist should result in a failed assert, but currently iplist seems to silently wrap to the head of the list on `end()++`. This is why the bad behavior is difficult to demonstrate. Reviewers: chandlerc, reames Subscribers: llvm-commits Differential Revision: http://reviews.llvm.org/D14350 llvm-svn: 252386
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llvm/test/Transforms/FunctionAttrs/out-of-bounds-iterator-bug.ll
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; RUN: opt -functionattrs -S < %s | FileCheck %s | ||
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; This checks for an iterator wraparound bug in FunctionAttrs. The previous | ||
; "incorrect" behavior was inferring readonly for the %x argument in @caller. | ||
; Inferring readonly for %x *is* actually correct, since @va_func is marked | ||
; readonly, but FunctionAttrs was inferring readonly for the wrong reasons (and | ||
; we _need_ the readonly on @va_func to trigger the problematic code path). It | ||
; is possible that in the future FunctionAttrs becomes smart enough to infer | ||
; readonly for %x for the right reasons, and at that point this test will have | ||
; to be marked invalid. | ||
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declare void @llvm.va_start(i8*) | ||
declare void @llvm.va_end(i8*) | ||
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define void @va_func(i32* readonly %b, ...) readonly nounwind { | ||
; CHECK-LABEL: define void @va_func(i32* nocapture readonly %b, ...) | ||
entry: | ||
%valist = alloca i8 | ||
call void @llvm.va_start(i8* %valist) | ||
call void @llvm.va_end(i8* %valist) | ||
%x = call i32 @caller(i32* %b) | ||
ret void | ||
} | ||
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define i32 @caller(i32* %x) { | ||
; CHECK-LABEL: define i32 @caller(i32* nocapture %x) | ||
entry: | ||
call void(i32*,...) @va_func(i32* null, i32 0, i32 0, i32 0, i32* %x) | ||
ret i32 42 | ||
} |