Constant pool should share values #35268
Description
Doubles added to constant pool are not shared: the same constant appearing multiple times appears multiple times in the constant pool.
Using the example from #35257:
private static double Process(double n)
{
double res;
res = 1;
while (n > 0.0)
{
res *= n;
// User might not write such code, but here it is written merely to show that same constants are re-loaded in assembly code.
n -= 1.0;
n -= 2.0;
n -= 1.0;
n -= 2.0;
}
return res;
}The generated x64 assembly is:
; Assembly listing for method BringUpTest:Process(double):double
; Emitting BLENDED_CODE for X64 CPU with AVX - Windows
; optimized code
; rsp based frame
; fully interruptible
; Final local variable assignments
;
; V00 arg0 [V00,T00] ( 13, 43 ) double -> mm0
; V01 loc0 [V01,T01] ( 4, 10 ) double -> mm1
;# V02 OutArgs [V02 ] ( 1, 1 ) lclBlk ( 0) [rsp+0x00] "OutgoingArgSpace"
;
; Lcl frame size = 0
G_M28499_IG01:
C5F877 vzeroupper
;; bbWeight=1 PerfScore 1.00
G_M28499_IG02:
C5FB100D4D000000 vmovsd xmm1, qword ptr [reloc @RWD00]
C5E857D2 vxorps xmm2, xmm2
C5F92EC2 vucomisd xmm0, xmm2
7638 jbe SHORT G_M28499_IG04
;; bbWeight=1 PerfScore 4.33
G_M28499_IG03:
C5F359C8 vmulsd xmm1, xmm1, xmm0
C5FB5C053F000000 vsubsd xmm0, xmm0, qword ptr [reloc @RWD08]
C5FB5C053F000000 vsubsd xmm0, xmm0, qword ptr [reloc @RWD16]
C5FB5C053F000000 vsubsd xmm0, xmm0, qword ptr [reloc @RWD24]
C5FB5C053F000000 vsubsd xmm0, xmm0, qword ptr [reloc @RWD32]
C5E857D2 vxorps xmm2, xmm2
C5F92EC2 vucomisd xmm0, xmm2
77D2 ja SHORT G_M28499_IG03
;; bbWeight=4 PerfScore 101.33
G_M28499_IG04:
C5F828C1 vmovaps xmm0, xmm1
;; bbWeight=1 PerfScore 0.25
G_M28499_IG05:
C3 ret
;; bbWeight=1 PerfScore 1.00
RWD00 dq 3FF0000000000000h
RWD08 dq 3FF0000000000000h
RWD16 dq 4000000000000000h
RWD24 dq 3FF0000000000000h
RWD32 dq 4000000000000000h
; Total bytes of code 72, prolog size 3, PerfScore 116.22, (MethodHash=7c9e90ac) for method BringUpTest:Process(double):double
; ============================================================
In this case, RWD00, RWD08, and RWD24 are identical, and RWD16 and RWD32 are identical.
The constant pool is (conceptually) read-only (I believe), so we only need one of each unique value in the table.
category:cq
theme:constant-pool
skill-level:intermediate
cost:medium