https://bugs.llvm.org/show_bug.cgi?id=35717
Bug ID: 35717
Summary: Regression for three way min/max
Product: libraries
Version: trunk
Hardware: PC
OS: Linux
Status: NEW
Severity: enhancement
Priority: P
Component: Scalar Optimizations
Assignee: unassignedb...@nondot.org
Reporter: david.gr...@arm.com
CC: llvm-bugs@lists.llvm.org
This is a regression that came in with rL320749. We have some code with three
way min/max that is now doing a lot worse than it did previously. The most
basic for I could come up with is this:
int test(int xc, int xm, int xy)
{
int xk;
if (xc < xm)
xk = xc < xy ? xc : xy;
else
xk = xm < xy ? xm : xy;
return xk;
}
This used to come out as (roughly "min(min(a,b),c)"):
define i32 @test(i32 %xc, i32 %xm, i32 %xy) {
entry:
%cmp = icmp slt i32 %xc, %xm
%xm.sink15 = select i1 %cmp, i32 %xc, i32 %xm
%cmp2 = icmp slt i32 %xm.sink15, %xy
%cond6 = select i1 %cmp2, i32 %xm.sink15, i32 %xy
ret i32 %cond6
}
But now ends up with extra selects (roughly "min(min(a,b), min(b,c))"):
define i32 @test(i32 %xc, i32 %xm, i32 %xy) {
entry:
%cmp = icmp slt i32 %xc, %xm
%cmp1 = icmp slt i32 %xc, %xy
%cond = select i1 %cmp1, i32 %xc, i32 %xy
%cmp2 = icmp slt i32 %xm, %xy
%cond6 = select i1 %cmp2, i32 %xm, i32 %xy
%xk.0 = select i1 %cmp, i32 %cond, i32 %cond6
ret i32 %xk.0
}
The original case came from a cmy conversion, where the values were i8 (not
i32) so there is a number of zext and trunc's making things more messy. They
are also inverted (subtracted from 255). It runs especially worse on our small
thumb1 cores.
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