JIT: some enhancements to redundant branch opts #60732
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Handle cases where the dominating compare is the reverse of the compare we're trying to optimize. For example, if `(x > y)` dominates `(y <= x)` we may be able to optimize the dominated compare. Addresses aspects of dotnet#48115.
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Tagging subscribers to this area: @JulieLeeMSFT Issue DetailsHandle cases where the dominating compare is the reverse of the compare Addresses aspects of #48115.
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cc @dotnet/jit-contrib Small number of regressions, mostly RA/CSE differences. aspnet.run.windows.x64.checked.mch:Detail diffsbenchmarks.run.windows.x64.checked.mch:Detail diffscoreclr_tests.pmi.windows.x64.checked.mch:Detail diffslibraries.crossgen2.windows.x64.checked.mch:Detail diffslibraries.pmi.windows.x64.checked.mch:Detail diffslibraries_tests.pmi.windows.x64.checked.mch:Detail diffsTypical diff ; Assembly listing for method System.Data.SqlClient.TdsParser:set_CurrentTransaction(System.Data.SqlClient.SqlInternalTransaction):this
; ...
; V00 this [V00,T01] ( 4, 3.50) ref -> rcx this class-hnd single-def
; V01 arg1 [V01,T00] ( 5, 3.50) ref -> rdx class-hnd single-def
;# V02 OutArgs [V02 ] ( 1, 1 ) lclBlk ( 0) [rsp+00H] "OutgoingArgSpace"
-; V03 cse0 [V03,T02] ( 3, 2.50) ref -> rax "CSE - aggressive"
;
; Lcl frame size = 0
@@ -17,23 +16,19 @@ G_M27428_IG01: ; gcrefRegs=00000000 {}, byrefRegs=00000000 {}, byref, nog
;; bbWeight=1 PerfScore 0.00
G_M27428_IG02: ; gcrefRegs=00000006 {rcx rdx}, byrefRegs=00000000 {}, byref, isz
; gcrRegs +[rcx rdx]
- mov rax, gword ptr [rcx+48]
- ; gcrRegs +[rax]
- test rax, rax
+ cmp gword ptr [rcx+48], 0
jne SHORT G_M27428_IG04
- ;; bbWeight=1 PerfScore 3.25
-G_M27428_IG03: ; gcrefRegs=00000007 {rax rcx rdx}, byrefRegs=00000000 {}, byref, isz
+ ;; bbWeight=1 PerfScore 4.00
+G_M27428_IG03: ; gcrefRegs=00000006 {rcx rdx}, byrefRegs=00000000 {}, byref, isz
test rdx, rdx
jne SHORT G_M27428_IG05
- ;; bbWeight=0.50 PerfScore 0.62
-G_M27428_IG04: ; gcrefRegs=00000007 {rax rcx rdx}, byrefRegs=00000000 {}, byref, isz
- test rax, rax
- je SHORT G_M27428_IG06
+ jmp SHORT G_M27428_IG06
+ ;; bbWeight=0.50 PerfScore 1.62
+G_M27428_IG04: ; gcrefRegs=00000006 {rcx rdx}, byrefRegs=00000000 {}, byref, isz
test rdx, rdx
jne SHORT G_M27428_IG06
- ;; bbWeight=0.50 PerfScore 1.25
+ ;; bbWeight=0.50 PerfScore 0.62
G_M27428_IG05: ; gcrefRegs=00000006 {rcx rdx}, byrefRegs=00000000 {}, byref
- ; gcrRegs -[rax]
lea rcx, bword ptr [rcx+48]
; gcrRegs -[rcx]
; byrRegs +[rcx]
@@ -48,7 +43,7 @@ G_M27428_IG07: ; , epilog, nogc, extend
ret
;; bbWeight=1 PerfScore 1.00
-; Total bytes of code 35, prolog size 0, PerfScore 10.63, instruction count 13, allocated bytes for code 35 (MethodHash=d2cb94db) for method System.Data.SqlClient.TdsParser:set_CurrentTransaction(System.Data.SqlClient.SqlInternalTransaction):this
+; Total bytes of code 30, prolog size 0, PerfScore 11.25, instruction count 11, allocated bytes for code 30 (MethodHash=d2cb94db) for method System.Data.SqlClient.TdsParser:set_CurrentTransaction(System.Data.SqlClient.SqlInternalTransaction):thisOne interesting regression, in |
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Nice! What about this case: both conditions are absolutely the same, just the order of operands is different. also, I assume this opt won't work for |
Not if sure all these cases are mapped to one standard form -- so probably worth looking at in more depth.
Good point, we should exclude fp compares here. Let's see if we get any failures from this in existing testing. |
A note to readers: this is because we do not model floating-pont |
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GCC build seems to be previously broken: See #60225 (comment) |
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@EgorBo I am also seeing the case you noted above (see below, messed-up example edited out) |
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[edit: removed obsolete / incorrect info] |
Unfortunately it seems this would require "further work", as it trips up the fragile range check elimination. |
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Above summary of adding support for swapped compares wasn't quite implemented properly. Updated diff of diffs is -131 total methods with Code Size differences (128 improved, 3 regressed), 14 unchanged.
-193 total methods with Code Size differences (171 improved, 22 regressed), 3 unchanged.
-421 total methods with Code Size differences (418 improved, 3 regressed), 5 unchanged.
-363 total methods with Code Size differences (343 improved, 20 regressed), 8 unchanged.
-1197 total methods with Code Size differences (1112 improved, 85 regressed), 45 unchanged.
-1241 total methods with Code Size differences (1156 improved, 85 regressed), 35 unchanged.
+134 total methods with Code Size differences (131 improved, 3 regressed), 14 unchanged.
+210 total methods with Code Size differences (185 improved, 25 regressed), 5 unchanged.
+385 total methods with Code Size differences (381 improved, 4 regressed), 5 unchanged.
+538 total methods with Code Size differences (519 improved, 19 regressed), 8 unchanged.
+1455 total methods with Code Size differences (1368 improved, 87 regressed), 53 unchanged.
+1281 total methods with Code Size differences (1196 improved, 85 regressed), 39 unchanged.One interesting example: We now produce the following odd looking bit of code... G_M030_IG01: ; gcVars=0000000000000000 {}, gcrefRegs=00000000 {}, byrefRegs=00000000 {}, gcvars, byref, nogc <-- Prolog IG
mov rax, rcx
; gcrRegs +[rax]
;; bbWeight=1 PerfScore 0.25
G_M030_IG02: ; gcrefRegs=00000001 {rax}, byrefRegs=00000000 {}, byref, isz
cmp dword ptr [rax+24], 0
jg SHORT G_M030_IG04
;; bbWeight=1 PerfScore 4.00
G_M030_IG03: ; gcrefRegs=00000001 {rax}, byrefRegs=00000000 {}, byref, epilog, nogc
ret
;; bbWeight=0.50 PerfScore 0.50
G_M030_IG04: ; gcrefRegs=00000001 {rax}, byrefRegs=00000000 {}, byref, epilog, nogc
ret |
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Updated diff summary aspnet.run.windows.x64.checked.mch:Detail diffsbenchmarks.run.windows.x64.checked.mch:Detail diffscoreclr_tests.pmi.windows.x64.checked.mch:Detail diffslibraries.crossgen2.windows.x64.checked.mch:Detail diffslibraries.pmi.windows.x64.checked.mch:Detail diffslibraries_tests.pmi.windows.x64.checked.mch:Detail diffs |
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@dotnet/jit-contrib ping |
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I must be missing something. In your example above, if I pass |
src/coreclr/jit/valuenum.cpp
Outdated
| // | ||
| // Arguments: | ||
| // vn - vn to base things on | ||
| // vnk - whether the new vn should swap, reverse, or both |
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Suggested change
| // vnk - whether the new vn should swap, reverse, or both | |
| // vrk - whether the new vn should swap, reverse, or both |
src/coreclr/jit/valuenum.cpp
Outdated
| // vn for reversed/swapped comparsion, or NoVN. | ||
| // | ||
| // Note: | ||
| // If "vn" corresponds to (x > y), the resulting VN correponds to |
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Suggested change
| // If "vn" corresponds to (x > y), the resulting VN correponds to | |
| // If "vn" corresponds to (x > y), the resulting VN corresponds to: |
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| // Note we could also infer the tree relop's value from similar relops higher in the dom tree. | ||
| // For example, (x >= 0) dominating (x > 0), or (x < 0) dominating (x > 0). | ||
| // | ||
| // That is left as a future enhancement. |
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Is this comment obsolete now? (Or in need of updating to match the new code)
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I'll update it -- there are still cases we don't get, like the first one listed.
Sorry about that. My example above was indeed messed up.... here's a corrected one that matches Egor's snippet static int F3(int x, int y)
{
int r = 0;
if (x > y)
{
r += 1;
if (y >= x) r += 2;
}
return r;
};;; base
; Assembly listing for method X:F3(int,int):int
; Emitting BLENDED_CODE for X64 CPU with AVX - Windows
; optimized code
; rsp based frame
; partially interruptible
; No PGO data
; Final local variable assignments
;
; V00 arg0 [V00,T00] ( 4, 3.50) int -> rcx single-def
; V01 arg1 [V01,T01] ( 4, 3.50) int -> rdx single-def
; V02 loc0 [V02,T02] ( 4, 3 ) int -> rax
;# V03 OutArgs [V03 ] ( 1, 1 ) lclBlk ( 0) [rsp+00H] "OutgoingArgSpace"
;
; Lcl frame size = 0
G_M37129_IG01: ;; offset=0000H
;; bbWeight=1 PerfScore 0.00
G_M37129_IG02: ;; offset=0000H
33C0 xor eax, eax
3BCA cmp ecx, edx
7E0E jle SHORT G_M37129_IG04
;; bbWeight=1 PerfScore 1.50
G_M37129_IG03: ;; offset=0006H
B801000000 mov eax, 1
3BD1 cmp edx, ecx
7C05 jl SHORT G_M37129_IG04
B803000000 mov eax, 3
;; bbWeight=0.50 PerfScore 0.88
G_M37129_IG04: ;; offset=0014H
C3 ret
;; bbWeight=1 PerfScore 1.00
; Total bytes of code 21, prolog size 0, PerfScore 5.48, instruction count 8, allocated bytes for code 21 (MethodHash=ddcb6ef6) for method X:F3(int,int):int
;;; diff
; Assembly listing for method X:F3(int,int):int
; Emitting BLENDED_CODE for X64 CPU with AVX - Windows
; optimized code
; rsp based frame
; partially interruptible
; No PGO data
; Final local variable assignments
;
; V00 arg0 [V00,T00] ( 3, 3 ) int -> rcx single-def
; V01 arg1 [V01,T01] ( 3, 3 ) int -> rdx single-def
; V02 loc0 [V02,T02] ( 3, 2.50) int -> rax
;# V03 OutArgs [V03 ] ( 1, 1 ) lclBlk ( 0) [rsp+00H] "OutgoingArgSpace"
;
; Lcl frame size = 0
G_M37129_IG01: ;; offset=0000H
;; bbWeight=1 PerfScore 0.00
G_M37129_IG02: ;; offset=0000H
33C0 xor eax, eax
3BCA cmp ecx, edx
7E05 jle SHORT G_M37129_IG04
;; bbWeight=1 PerfScore 1.50
G_M37129_IG03: ;; offset=0006H
B801000000 mov eax, 1
;; bbWeight=0.50 PerfScore 0.12
G_M37129_IG04: ;; offset=000BH
C3 ret
;; bbWeight=1 PerfScore 1.00
; Total bytes of code 12, prolog size 0, PerfScore 3.83, instruction count 5, allocated bytes for code 12 (MethodHash=ddcb6ef6) for method X:F3(int,int):int |
BruceForstall
approved these changes
Oct 23, 2021
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Handle cases where the dominating compare is the reverse of the compare
we're trying to optimize. For example, if
(x > y)dominates(y <= x)we may be able to optimize the dominated compare.
Addresses aspects of #48115.