https://bugs.llvm.org/show_bug.cgi?id=41348
Bug ID: 41348
Summary: [X86] Failure to move indvar constant offset into
final address gen
Product: libraries
Version: trunk
Hardware: PC
OS: Windows NT
Status: NEW
Severity: enhancement
Priority: P
Component: Backend: X86
Assignee: unassignedb...@nondot.org
Reporter: llvm-...@redking.me.uk
CC: andrea.dibia...@gmail.com, craig.top...@gmail.com,
llvm-bugs@lists.llvm.org, llvm-...@redking.me.uk,
spatel+l...@rotateright.com
https://gcc.godbolt.org/z/Z2uB_v
<snip>
leal 1(%rdx), %eax
leaq (%rax,%rax,2), %rax
movq %r9, (%rdi,%rax,8)
leal 2(%rdx), %eax
leaq (%rax,%rax,2), %rax
movq %r11, (%rdi,%rax,8)
leal 3(%rdx), %eax
leaq (%rax,%rax,2), %rax
movq %rcx, (%rdi,%rax,8)
<snip>
leal 31(%rdx), %eax
leaq (%rax,%rax,2), %rax
movq %rcx, (%rdi,%rax,8)
It'd be much better to just do the "leaq (%rax,%rax,2), %rax" once without the
offset and add the constant offset into the memory op address. Even for
hardware that doesn't like complex LEA this should be a definite win.
Something like (I haven't thoroughly check the trunc/zext effects):
leaq (%rdx,%rdx,2), %eax
movq %r9, 3,(%rdi,%rax,8)
movq %r11, 6,(%rdi,%rax,8)
movq %rcx, 9(%rdi,%rax,8)
<snip>
movq %rcx, 93(%rdi,%rax,8)
--
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