JIT: Lowering's insertion of `PUTARG_*` nodes is questionable

[jakobbotsch]

When we lower arguments to calls we create PUTARG_* nodes and insert them right after their corresponding argument definitions:

runtime/src/coreclr/jit/lower.cpp

Lines 1510 to 1511 in d06fb08

	// Insert the putarg/copy into the block
	BlockRange().InsertAfter(arg, putArgOrBitcast);

This insertion location does not make sense, since conceptually the definitions of the argument nodes can be arbitrarily far away from the call and there can even be interfering calls between the argument and consuming call.

The choice was probably made because the argument placement order is decided during morph when the call is in tree order, and the expectation is that args are placed in the early/late order decided there.

A few potential fixes:

• Insert PUTARG nodes during rationalization when we can depend on tree order and the early/late args call invariant. Seems to move something that is conceptually ABI lowering into rationalization which is unfortunate.
• Insert the PUTARG nodes right before the call node. Unfortunately has large regressions.
• Check for call interference between the arg and call and place the argument early on no interference and late on interference. Probably costs some TP.
• Move arg lowering from morph to lowering with appropriate interference checking (similar to what morph has to do today anyway). Probably best long term solution, but takes the most work.

cc @dotnet/jit-contrib

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[jakobbotsch]

We do have cases today where we end up with interfering CALL nodes between a PUTARG_STK and a call, specifically because of the BULKWRITEBARRIER transformation introducing a call between a temp store for a late argument and its corresponding call.

For example:

****** START compiling Microsoft.CodeAnalysis.Compilation:SerializePeToStream(Microsoft.CodeAnalysis.Emit.CommonPEModuleBuilder,Microsoft.CodeAnalysis.DiagnosticBag,Microsoft.CodeAnalysis.CommonMessageProvider,System.Func`1[System.IO.Stream],System.Func`1[System.IO.Stream],System.Func`1[System.IO.Stream],Microsoft.Cci.PdbWriter,System.String,Microsoft.CodeAnalysis.RebuildData,ubyte,ubyte,ubyte,ubyte,System.Nullable`1[System.Security.Cryptography.RSAParameters],System.Threading.CancellationToken):ubyte (MethodHash=c9b17aac)

...

N001 (  3,  2) [000037] -----------                   t37 =    LCL_VAR   ref    V06 arg6         u:1 (last use) $86
                                                            ┌──▌  t37    ref    
               [000270] -----------                         ▌  PUTARG_STK [+0x20] void  
N002 (  3,  2) [000038] -----------                   t38 =    LCL_VAR   ref    V07 arg7         u:1 (last use) $87
                                                            ┌──▌  t38    ref    
               [000271] -----------                         ▌  PUTARG_STK [+0x28] void  
N003 (  1,  1) [000228] -----------                  t228 =    LCL_VAR   int    V29 cse0         u:1 $181
                                                            ┌──▌  t228   int    
               [000272] -----------                         ▌  PUTARG_STK [+0x30] void  
N004 (  3,  2) [000040] -----------                   t40 =    LCL_VAR   int    V17 loc2         u:2 (last use) $18a
                                                            ┌──▌  t40    int    
               [000273] -----------                         ▌  PUTARG_STK [+0x38] void  
N005 (  3,  2) [000041] -----------                   t41 =    LCL_VAR   int    V12 arg12        u:1 (last use) $c3
                                                            ┌──▌  t41    int    
N006 (  4,  4) [000200] -----------                  t200 = ▌  CAST      int <- ubyte <- int $18e
                                                            ┌──▌  t200   int    
               [000274] -----------                         ▌  PUTARG_STK [+0x40] void  
               [000261] D----------                  t261 =    LCL_ADDR  byref  V28 tmp10        [+0]
                                                            ┌──▌  t261   byref  
               [000267] -----------                  t267 = ▌  PUTARG_REG byref  REG rcx
N007 (  1,  1) [000042] -----------                   t42 =    LCL_VAR   byref  V13 arg13        u:1 $100
                                                            ┌──▌  t42    byref  
               [000268] -----------                  t268 = ▌  PUTARG_REG byref  REG rdx
               [000262] -----------                  t262 =    CNS_INT   long   72
                                                            ┌──▌  t262   long   
               [000269] -----------                  t269 = ▌  PUTARG_REG long   REG r8
                                                            ┌──▌  t267   byref  arg0 in rcx
                                                            ├──▌  t268   byref  arg1 in rdx
                                                            ├──▌  t269   long   arg2 in r8
N004 ( 17, 11) [000266] --CXG------                         ▌  CALL help void   CORINFO_HELP_BULK_WRITEBARRIER
N009 ( 17, 12) [000202] -----------                            NOP       void  
N010 (  3,  2) [000043] -----------                   t43 =    LCL_VAR   ref    V25 tmp7         u:1 $89
                                                            ┌──▌  t43    ref    
               [000275] -----------                         ▌  PUTARG_STK [+0x50] void  
N011 (  3,  3) [000203] -----------                  t203 =    LCL_ADDR  long   V28 tmp10        [+0] $280
                                                            ┌──▌  t203   long   
               [000276] -----------                         ▌  PUTARG_STK [+0x48] void  
N012 (  3,  3) [000033] -----------                   t33 =    LCL_ADDR  long   V21 tmp3         [+0] $281
                                                            ┌──▌  t33    long   
               [000277] -----------                  t277 = ▌  PUTARG_REG long   REG rcx
N013 (  1,  1) [000034] -----------                   t34 =    LCL_VAR   ref    V02 arg2         u:1 $82
                                                            ┌──▌  t34    ref    
               [000278] -----------                  t278 = ▌  PUTARG_REG ref    REG rdx
N014 (  1,  1) [000035] -----------                   t35 =    LCL_VAR   ref    V03 arg3         u:1 (last use) $83
                                                            ┌──▌  t35    ref    
               [000279] -----------                  t279 = ▌  PUTARG_REG ref    REG r8
N015 (  3,  2) [000036] -----------                   t36 =    LCL_VAR   ref    V05 arg5         u:1 (last use) $85
                                                            ┌──▌  t36    ref    
               [000280] -----------                  t280 = ▌  PUTARG_REG ref    REG r9
N001 (  3, 10) [000281] Hc---------                  t281 =    CNS_INT(h) long   0x7fff099345a0 ftn
                                                            ┌──▌  t281   long   
N002 (  5, 12) [000282] nc--G------                  t282 = ▌  IND       long   REG NA
                                                            ┌──▌  t277   long   arg0 in rcx
                                                            ├──▌  t278   ref    arg1 in rdx
                                                            ├──▌  t279   ref    arg2 in r8
                                                            ├──▌  t280   ref    arg3 in r9
                                                            ├──▌  t282   long   control expr
N016 ( 80, 45) [000044] -ACXG------                   t44 = ▌  CALL      int    <unknown method> $2c0