JIT: Optimize *x = dblCns to *x = intCns

[EgorBo]

Just a small optimization for #52286 (comment) comment.

void Test(ref float x) => x = 0;

Current codegen:

; Method Program:Test(byref)
G_M20809_IG01:
       vzeroupper 
						;; bbWeight=1    PerfScore 1.00
G_M20809_IG02:
       vxorps   xmm0, xmm0
       vmovss   dword ptr [rcx], xmm0
						;; bbWeight=1    PerfScore 0.83
G_M20809_IG03:
       ret      
						;; bbWeight=1    PerfScore 1.00
; Total bytes of code: 12

New codegen:

; Method Program:Test(byref)
G_M20809_IG02:
       mov      dword ptr [rcx], 0
						;; bbWeight=1    PerfScore 1.00
G_M20809_IG03:
       ret      
						;; bbWeight=1    PerfScore 1.00
; Total bytes of code: 7

SuperPMI results:

asm.aspnet.run.windows.x64.checked.2               -86 (-0.21% of base)
asm.benchmarks.run.windows.x64.checked            -684 (-1.02% of base)
asm.libraries.crossgen.windows.x64.checked.3      -641 (-0.78% of base)
asm.libraries.crossgen2.windows.x64.checked.2     -600 (-0.77% of base)
asm.libraries.pmi.windows.x64.checked             -967 (-0.99% of base)
asm.tests_libraries.pmi.windows.x64.checked     -25294 (-0.72% of base)
asm.tests.pmi.windows.x64.checked.1             -71306 (-0.35% of base)

/cc @dotnet/jit-contrib @SingleAccretion

[tannergooding]

Changes LGTM.

[EgorBo]

@dotnet/jit-contrib @tannergooding anyone wants to approve? 🙂