This program runs about 6 times faster compiled with ldc2 compared to dmd (I run it with 100000000 command line argument): import core.stdc.stdio, std.random, std.conv; void main(in string[] args) { immutable uint N = (args.length == 2) ? args[1].to!uint : 1_000; auto rng = Xorshift(0); uint total = 0; for (uint i = 0; i < N; i++) total += uniform(0, 10, rng); printf("%u\n", total); } If I replace this line: total += uniform(0, 10, rng); with: total += rng.front; rng.popFront; Then the code compiled with ldc2 is only about 30% faster. dmd 2.064alpha, -O -release -inline -noboundscheck. Ldc2 V. 0.11.0, based on DMD v2.062 and LLVM 3.3svn, -O5 -release -profile-verifier-noassert.
This alternative version of the program is handy to produce a more readable asm output: import core.stdc.stdio: printf; import core.stdc.stdlib: atoi; import std.random: Xorshift, uniform; uint randomSum(in uint n, Xorshift rng) { uint total = 0; for (uint i = 0; i < n; i++) total += uniform(0, 10, rng); return total; } void main(in string[] args) { immutable uint N = (args.length == 2) ? atoi((args[1] ~ '\0').ptr) : 1_000; auto rng = Xorshift(0); immutable result = randomSum(N, rng); printf("%u\n", result); } LDC2 produces for the randomSum() function (the inner loop is 26 instructions long, with no call instructions): __D4temp9randomSumFxkS3std6random38__T14XorshiftEngineTkVi128Vi11Vi8Vi19Z14XorshiftEngineZk: pushl %ebp pushl %ebx pushl %edi pushl %esi pushl %eax xorl %eax, %eax cmpl $0, 40(%esp) je LBB0_5 leal 24(%esp), %ecx movl 8(%ecx), %esi movl (%ecx), %eax movl 4(%ecx), %edx movl 12(%ecx), %ebp xorl %ebx, %ebx movl $0, (%esp) .align 16, 0x90 LBB0_2: movl %esi, %edi movl %edx, %ecx movl %ebp, %esi movl %eax, %ebp shll $11, %ebp xorl %eax, %ebp movl %esi, %eax shrl $19, %eax xorl %esi, %eax xorl %ebp, %eax shrl $8, %ebp xorl %eax, %ebp cmpl $-7, %esi movl %edi, %edx movl %ecx, %eax ja LBB0_2 movl %esi, %eax movl $671088641, %edx mull %edx shrl $26, %edx addl %edx, (%esp) incl %ebx cmpl 40(%esp), %ebx movl %edi, %edx movl %ecx, %eax jne LBB0_2 leal 24(%esp), %eax movl %ebp, 12(%eax) movl %ecx, (%eax) movl %edi, 4(%eax) movl %esi, 8(%eax) movl (%esp), %eax LBB0_5: addl $4, %esp popl %esi popl %edi popl %ebx popl %ebp ret $20 Maybe it's also a matter of missed inlining.