%rsp emitted as an index register

[sunfishcode]

Bugzilla Link	1103
Resolution	FIXED
Resolved on	Feb 22, 2010 12:51
Version	1.9
OS	Linux
Attachments	test case

Extended Description

The x86 backend allows %rsp to be used as an index register in an address
operand. Some assemblers accept this and automatically rewrite it so that %rsp
is the base register to make it legal, but some don't, including GAS.

[sunfishcode]

assigned to @lattner

[lattner]

To clarify, you're saying that:
leaq 16(%r10,%rsp), %r10

should be:

leaq 16(%rsp,%r10), %r10

?

[lattner]

okay, right. The official syntax is:
section:disp(base, index, scale)

[lattner]

This looks like a register coallescing issue. llc -print-machineinstrs shows this after isel:

    %reg1165 = CMOVS64rr %reg1032, %reg1163
    %reg1038 = SUB32rr %reg1025, %reg1024
    %reg1034 = MOV64rr %RSP

...
%reg1037 = LEA64r %reg1166, 1, %reg1034, 16
%reg1036 = LEA64r %reg1164, 1, %reg1034, 16

When reg1034 is coallesced with RSP, we get the problem.

[lattner]

The most straight-forward way to fix this is in the asmprinter. Addressed with this patch:
http://lists.cs.uiuc.edu/pipermail/llvm-commits/Week-of-Mon-20070108/042639.html

Testcase here:
Regression/CodeGen/X86/2007-01-13-StackPtrIndex.ll

-Chris