Evan Cheng
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8a7186dbc2
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Let targets provide hooks that compute known zero and ones for any_extend
and extload's. If they are implemented as zero-extend, or implicitly
zero-extend, then this can enable more demanded bits optimizations. e.g.
define void @foo(i16* %ptr, i32 %a) nounwind {
entry:
%tmp1 = icmp ult i32 %a, 100
br i1 %tmp1, label %bb1, label %bb2
bb1:
%tmp2 = load i16* %ptr, align 2
br label %bb2
bb2:
%tmp3 = phi i16 [ 0, %entry ], [ %tmp2, %bb1 ]
%cmp = icmp ult i16 %tmp3, 24
br i1 %cmp, label %bb3, label %exit
bb3:
call void @bar() nounwind
br label %exit
exit:
ret void
}
This compiles to the followings before:
push {lr}
mov r2, #0
cmp r1, #99
bhi LBB0_2
@ BB#1: @ %bb1
ldrh r2, [r0]
LBB0_2: @ %bb2
uxth r0, r2
cmp r0, #23
bhi LBB0_4
@ BB#3: @ %bb3
bl _bar
LBB0_4: @ %exit
pop {lr}
bx lr
The uxth is not needed since ldrh implicitly zero-extend the high bits. With
this change it's eliminated.
rdar://12771555
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@169459 91177308-0d34-0410-b5e6-96231b3b80d8
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2012-12-06 01:28:01 +00:00 |
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