And older, about amd64 in general (x86/32bit is quite different from 64bit):
"lea -0x30(%edx,%esi,8),%esi
Compute the address %edx+8*%esi-48, but don’t refer to the contents of memory. Instead, store the address itself into register %esi. This is the “load effective address” instruction: its binary coding is short, it doesn’t
tie up the integer unit, and it doesn’t set the flags."
[ed: in general the purpose of lea is to get the address of things in c/pascal arrays (pointer to array+offset) -- as I understand it. I don't know if it's used for other tricks by optimizing (c) compilers much -- but taking the address of an item in an array (say a character in a C string) sounds like it would be fairly common. If lea is fast(er) on amd64 using the dedicated operand would make sense.]
Yeah, despite it's name, lea is an arithmetic instruction; it doesn't reference memory (although it was designed with computing memory addresses in mind). You can do some neat arithmetic tricks with lea, because it computes register1 + register2<<shift + offset.
http://www.realworldtech.com/haswell-cpu/4/
And older, about amd64 in general (x86/32bit is quite different from 64bit):
"lea -0x30(%edx,%esi,8),%esi
Compute the address %edx+8*%esi-48, but don’t refer to the contents of memory. Instead, store the address itself into register %esi. This is the “load effective address” instruction: its binary coding is short, it doesn’t tie up the integer unit, and it doesn’t set the flags."
http://people.freebsd.org/~lstewart/references/amd64.pdf
[ed: in general the purpose of lea is to get the address of things in c/pascal arrays (pointer to array+offset) -- as I understand it. I don't know if it's used for other tricks by optimizing (c) compilers much -- but taking the address of an item in an array (say a character in a C string) sounds like it would be fairly common. If lea is fast(er) on amd64 using the dedicated operand would make sense.]