This patch teaches IndVarSimplify to add nuw and nsw to certain kinds
of operations that provably don't overflow. For example, we can prove
%civ.inc below does not sign-overflow. With this change,
IndVarSimplify changes %civ.inc to an add nsw.
define i32 @foo(i32* %array, i32* %length_ptr, i32 %init) {
entry:
%length = load i32* %length_ptr, !range !0
%len.sub.1 = sub i32 %length, 1
%upper = icmp slt i32 %init, %len.sub.1
br i1 %upper, label %loop, label %exit
loop:
%civ = phi i32 [ %init, %entry ], [ %civ.inc, %latch ]
%civ.inc = add i32 %civ, 1
%cmp = icmp slt i32 %civ.inc, %length
br i1 %cmp, label %latch, label %break
latch:
store i32 0, i32* %array
%check = icmp slt i32 %civ.inc, %len.sub.1
br i1 %check, label %loop, label %break
break:
ret i32 %civ.inc
exit:
ret i32 42
}
Differential Revision: http://reviews.llvm.org/D6748
llvm-svn: 225282
