Chawla, Pankaj via llvm-dev
2019-Aug-20 22:43 UTC
[llvm-dev] missing simplification in ScalarEvolution?
Hi,
I have this small test case-
%struct1 = type { i32, i32 }
@glob_const = internal constant [4 x %struct1] [%struct1 { i32 4, i32 5 },
%struct1 { i32 8, i32 9 }, %struct1 { i32 16, i32 0 }, %struct1 { i32 32, i32 10
}], align 16
define void @foo() {
entry:
br label %loop
loop: ; preds = %loop, %entry
%iv = phi %struct1* [ getelementptr inbounds ([4 x %struct1], [4 x %struct1]*
@glob_const, i64 0, i64 0), %entry ], [ %iv.inc, %loop ]
%gep = getelementptr inbounds %struct1, %struct1* %iv, i64 0, i32 0
%ld = load i32, i32* %gep, align 8
%iv.inc = getelementptr inbounds %struct1, %struct1* %iv, i64 1
%cmp = icmp ult %struct1* %iv.inc, getelementptr inbounds ([4 x %struct1], [4
x %struct1]* @glob_const, i64 1, i64 0)
br i1 %cmp, label %loop, label %exit
exit:
ret void
}
I was expecting the backedge taken count of the loop to be evaluated to 3 by
ScalarEvolution but instead it evaluates to this-
Loop %loop: backedge-taken count is ((-1 + (-1 * @glob_const) + ((8 +
@glob_const)<nuw><nsw> umax (32 + @glob_const)<nsw>)) /u 8)
Loop %loop: max backedge-taken count is 3, actual taken count either this or
zero.
Can we deduce the final value of the IV (32 + @glob_const) to be greater than
the initial value (8 + @glob_const) and simplify the backedge taken count to 3?
Thanks,
Pankaj
Philip Reames via llvm-dev
2019-Aug-21 00:26 UTC
[llvm-dev] missing simplification in ScalarEvolution?
Try adding a datalayout with pointer size information to your reduced case, and see what happens. Not sure this is your problem, but I've been bitten by this before with hand reduced examples... Philip On 8/20/19 3:43 PM, Chawla, Pankaj via llvm-dev wrote:> Hi, > > I have this small test case- > > %struct1 = type { i32, i32 } > > @glob_const = internal constant [4 x %struct1] [%struct1 { i32 4, i32 5 }, %struct1 { i32 8, i32 9 }, %struct1 { i32 16, i32 0 }, %struct1 { i32 32, i32 10 }], align 16 > > define void @foo() { > entry: > br label %loop > > loop: ; preds = %loop, %entry > %iv = phi %struct1* [ getelementptr inbounds ([4 x %struct1], [4 x %struct1]* @glob_const, i64 0, i64 0), %entry ], [ %iv.inc, %loop ] > %gep = getelementptr inbounds %struct1, %struct1* %iv, i64 0, i32 0 > %ld = load i32, i32* %gep, align 8 > %iv.inc = getelementptr inbounds %struct1, %struct1* %iv, i64 1 > %cmp = icmp ult %struct1* %iv.inc, getelementptr inbounds ([4 x %struct1], [4 x %struct1]* @glob_const, i64 1, i64 0) > br i1 %cmp, label %loop, label %exit > > exit: > ret void > } > > I was expecting the backedge taken count of the loop to be evaluated to 3 by ScalarEvolution but instead it evaluates to this- > > Loop %loop: backedge-taken count is ((-1 + (-1 * @glob_const) + ((8 + @glob_const)<nuw><nsw> umax (32 + @glob_const)<nsw>)) /u 8) > Loop %loop: max backedge-taken count is 3, actual taken count either this or zero. > > > Can we deduce the final value of the IV (32 + @glob_const) to be greater than the initial value (8 + @glob_const) and simplify the backedge taken count to 3? > > Thanks, > Pankaj > _______________________________________________ > LLVM Developers mailing list > llvm-dev at lists.llvm.org > https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
Chawla, Pankaj via llvm-dev
2019-Aug-21 00:35 UTC
[llvm-dev] missing simplification in ScalarEvolution?
Thanks for the suggestion but datalayout info did not solve the problem! -Pankaj -----Original Message----- From: Philip Reames <listmail at philipreames.com> Sent: Tuesday, August 20, 2019 5:26 PM To: Chawla, Pankaj <pankaj.chawla at intel.com>; llvm-dev at lists.llvm.org Subject: Re: [llvm-dev] missing simplification in ScalarEvolution? Try adding a datalayout with pointer size information to your reduced case, and see what happens. Not sure this is your problem, but I've been bitten by this before with hand reduced examples... Philip On 8/20/19 3:43 PM, Chawla, Pankaj via llvm-dev wrote:> Hi, > > I have this small test case- > > %struct1 = type { i32, i32 } > > @glob_const = internal constant [4 x %struct1] [%struct1 { i32 4, i32 > 5 }, %struct1 { i32 8, i32 9 }, %struct1 { i32 16, i32 0 }, %struct1 { > i32 32, i32 10 }], align 16 > > define void @foo() { > entry: > br label %loop > > loop: ; preds = %loop, %entry > %iv = phi %struct1* [ getelementptr inbounds ([4 x %struct1], [4 x %struct1]* @glob_const, i64 0, i64 0), %entry ], [ %iv.inc, %loop ] > %gep = getelementptr inbounds %struct1, %struct1* %iv, i64 0, i32 0 > %ld = load i32, i32* %gep, align 8 > %iv.inc = getelementptr inbounds %struct1, %struct1* %iv, i64 1 > %cmp = icmp ult %struct1* %iv.inc, getelementptr inbounds ([4 x %struct1], [4 x %struct1]* @glob_const, i64 1, i64 0) > br i1 %cmp, label %loop, label %exit > > exit: > ret void > } > > I was expecting the backedge taken count of the loop to be evaluated > to 3 by ScalarEvolution but instead it evaluates to this- > > Loop %loop: backedge-taken count is ((-1 + (-1 * @glob_const) + ((8 + > @glob_const)<nuw><nsw> umax (32 + @glob_const)<nsw>)) /u 8) Loop %loop: max backedge-taken count is 3, actual taken count either this or zero. > > > Can we deduce the final value of the IV (32 + @glob_const) to be greater than the initial value (8 + @glob_const) and simplify the backedge taken count to 3? > > Thanks, > Pankaj > _______________________________________________ > LLVM Developers mailing list > llvm-dev at lists.llvm.org > https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev