Support loop cloning with non-int iteration variables

[BruceForstall]

Loops with byte/short iteration variables:

for (byte i = 0; i < 100; i++)
{
    a[i] = 0;
}

create an iteration increment tree with a CAST node:

***** BB03
STMT00003 ( 0x00E[E-] ... 0x012 )
               [000025] -A---+-----                         *  ASG       int
               [000024] D----+-N---                         +--*  LCL_VAR   int    V01 loc0
               [000023] -----+-----                         \--*  CAST      int <- ubyte <- int
               [000022] -----+-----                            \--*  ADD       int
               [000020] -----+-----                               +--*  LCL_VAR   int    V01 loc0
               [000021] -----+-----                               \--*  CNS_INT   int    1

This pattern is not matched by GenTree::IsLclVarUpdateTree().

Loops with long iteration variables:

for (long i = 0; i < 100; i++)
{
    a[i] = 0;
}

create (naturally) an increment constant that is long typed:

STMT00003 ( 0x00B[E-] ... 0x00F )
               [000022] -A---+-----                         *  ASG       long
               [000021] D----+-N---                         +--*  LCL_VAR   long   V01 loc0
               [000020] -----+-----                         \--*  ADD       long
               [000017] -----+-----                            +--*  LCL_VAR   long   V01 loc0
               [000019] -----+-----                            \--*  CNS_INT   long   1

and that is screened out by Compiler::optIsLoopIncrTree():

        if ((incrVal->gtOper != GT_CNS_INT) || (incrVal->TypeGet() != TYP_INT))

category:cq
theme:loop-opt
skill-level:expert
cost:small
impact:small

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Issue Details

---

Loops with byte/short iteration variables:

for (byte i = 0; i < 100; i++)
{
    a[i] = 0;
}

create an iteration increment tree with a CAST node:

***** BB03
STMT00003 ( 0x00E[E-] ... 0x012 )
               [000025] -A---+-----                         *  ASG       int
               [000024] D----+-N---                         +--*  LCL_VAR   int    V01 loc0
               [000023] -----+-----                         \--*  CAST      int <- ubyte <- int
               [000022] -----+-----                            \--*  ADD       int
               [000020] -----+-----                               +--*  LCL_VAR   int    V01 loc0
               [000021] -----+-----                               \--*  CNS_INT   int    1

This pattern is not matched by GenTree::IsLclVarUpdateTree().

Loops with long iteration variables:

for (long i = 0; i < 100; i++)
{
    a[i] = 0;
}

create (naturally) an increment constant that is long typed:

STMT00003 ( 0x00B[E-] ... 0x00F )
               [000022] -A---+-----                         *  ASG       long
               [000021] D----+-N---                         +--*  LCL_VAR   long   V01 loc0
               [000020] -----+-----                         \--*  ADD       long
               [000017] -----+-----                            +--*  LCL_VAR   long   V01 loc0
               [000019] -----+-----                            \--*  CNS_INT   long   1

and that is screened out by Compiler::optIsLoopIncrTree():

        if ((incrVal->gtOper != GT_CNS_INT) || (incrVal->TypeGet() != TYP_INT))

category:cq
theme:loop-opt
skill-level:expert
cost:small
impact:small

Author:	BruceForstall
Assignees:	BruceForstall
Labels:	area-CodeGen-coreclr
Milestone:	Future

[BruceForstall]

For the long iteration var case, there are (at least) these additional things:

The array length node ARR_LENGTH has a cast on top, which Compiler::optExtractArrIndex() doesn't recognize:

*  COMMA     byref
+--*  BOUNDS_CHECK_Rng void
|  +--*  LCL_VAR   long   V01 loc0
|  \--*  CAST      long <- uint
|     \--*  ARR_LENGTH int
|        \--*  LCL_VAR   ref    V00 arg0
\--*  ARR_ADDR  byref byte[]
   \--*  ADD       byref
      +--*  LCL_VAR   ref    V00 arg0
      \--*  ADD       long
         +--*  LCL_VAR   long   V01 loc0
         \--*  CNS_INT   long   16

The iteration variable is expected to be TYP_INT in Compiler::optCheckIterInLoopTest().

Compiler::optDeriveLoopCloningConditions() requires the initLcl var to be TYP_INT.

LC_Ident constants are assumed to be TYP_INT.

LC_Condition::ToGenTree() assumes TYP_INT.

LC_Array::ToGenTree() uses gtNewArrLen(TYP_INT,...), which is correct, but we need to re-insert the cast up to LONG if necessary.