https://bugs.llvm.org/show_bug.cgi?id=46717
Bug ID: 46717
Summary: Bug in pass 'ipsccp' on function attribute
'argmemonly'.
Product: tools
Version: trunk
Hardware: All
OS: All
Status: NEW
Severity: normal
Priority: P
Component: opt
Assignee: unassignedb...@nondot.org
Reporter: fangqin...@gmail.com
CC: llvm-bugs@lists.llvm.org
When pass 'ipsccp' replaces arguments with global variables, it forgets to
remove the function's 'argmemonly' attribute. Which may cause wrong behavior,
just like following test case(from Alexandre Isoard) shows:
********************************************************
; RUN: opt -ipsccp -deadargelim -licm -O2 -S < %s
@g = internal global i32 0
; Function Attrs: argmemonly
define internal void @foo(i32* nonnull dereferenceable(4) %arg, i32 %val) #0 {
entry:
store i32 %val, i32* %arg
ret void
}
define i32 @bar(i32 %n) {
entry:
store i32 1, i32* @g
br label %loop
loop: ; preds = %bb1, %bb
%i = phi i32 [ %i.inc, %loop ], [ 0, %entry ]
%g.val = load i32, i32* @g
%g.inc = add nuw i32 %g.val, 1
tail call void @foo(i32* @g, i32 %g.inc)
%i.inc = add nuw i32 %i, 1
%cond = icmp eq i32 %i.inc, %n
br i1 %cond, label %exit, label %loop
exit: ; preds = %bb1
ret i32 %g.val
}
declare void @llvm.assume(i1)
attributes #0 = { argmemonly }
********************************************************
Before 'ipsccp', function '@foo' is marked with 'argmemonly' attribute. But
after the argument '%arg' is replaced with '@g' by pass 'ipsccp', attribute
'argmemonly' is left there. And due to the 'argmemonly' attribute, pass 'licm'
will think the value of global variable '@g' is not changed (but it is
changed), then hoist the load of the '@g' outside the loop. And cause function
'@bar' return wrong value '1'. But the correct return value should be '%n'.
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