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Signed division performed even when values are provably non-negative #94218
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Tagging subscribers to this area: @JulieLeeMSFT, @jakobbotsch Issue DetailsRepro: static int Result(int i)
{
if (i < 4) return 0;
return i / 4;
} This results in: ; Method Program:<<Main>$>g__Result|0_0(int):int (FullOpts)
G_M000_IG01: ;; offset=0x0000
G_M000_IG02: ;; offset=0x0000
cmp ecx, 4
jge SHORT G_M000_IG05
G_M000_IG03: ;; offset=0x0005
xor eax, eax
G_M000_IG04: ;; offset=0x0007
ret
G_M000_IG05: ;; offset=0x0008
mov eax, ecx
sar eax, 31
and eax, 3
add eax, ecx
sar eax, 2
G_M000_IG06: ;; offset=0x0015
ret
; Total bytes of code: 22 but as the JIT can prove that the static int Result(int i)
{
if (i < 4) return 0;
return (int)((uint)i / 4);
} were instead used? And it results in: ; Method Program:<<Main>$>g__Result|0_0(int):int (FullOpts)
G_M000_IG01: ;; offset=0x0000
G_M000_IG02: ;; offset=0x0000
cmp ecx, 4
jge SHORT G_M000_IG05
G_M000_IG03: ;; offset=0x0005
xor eax, eax
G_M000_IG04: ;; offset=0x0007
ret
G_M000_IG05: ;; offset=0x0008
mov eax, ecx
shr eax, 2
G_M000_IG06: ;; offset=0x000D
ret
; Total bytes of code: 14
|
As just an observer here, it seems JIT can prove the sign of |
It's already supposed to: runtime/src/coreclr/jit/morph.cpp Lines 8510 to 8517 in f2e4ddf
|
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While #94347 fixes your example, we might still have a few cases where we won't optimize, e.g. when JIT expands |
Repro:
This results in:
but as the JIT can prove that the
i
used ini / 4
isn't negative, so presumably it should be able to emit the code as if:were instead used? And it results in:
The text was updated successfully, but these errors were encountered: