http://llvm.org/bugs/show_bug.cgi?id=12173
Bug #: 12173
Summary: incorrect shrdq instruction from __asm__() directive
Product: clang
Version: 3.0
Platform: Macintosh
OS/Version: MacOS X
Status: NEW
Severity: normal
Priority: P
Component: LLVM Codegen
AssignedTo: [email protected]
ReportedBy: [email protected]
CC: [email protected]
Classification: Unclassified
Created attachment 8139
--> http://llvm.org/bugs/attachment.cgi?id=8139
minimal c code to demonstrate __asm__() shrdq bug
This issue was discovered on clang 3.0, and reproduced on clang 3.1 in Xcode
4.3:
>>Apple clang version 3.1 (tags/Apple/clang-318.0.45) (based on LLVM 3.1svn)
>>Target: x86_64-apple-darwin11.3.0
/*
* Using the 2-argument form of the shrdq instruction (i.e. with %cl implicit),
* clang generates the following __asm__() directive as:
* shrdq $0x01,%rax,%rdx // shift %rdx right 1 bit (immediate addressing!)
filling from %rax
* Expected instruction:
* shrdq %cl,%rdx,%rax // shift %rax right by %cl bits, filling from
%rdx
*
* Gcc generates the expected instruction from this __asm__() directive.
*/
unsigned long long
badshift(unsigned long long lo64,
unsigned long long hi64,
unsigned char shift)
{
__asm__("shrdq %1, %0" /* XXX => shrdq $0x01,%rax,%rdx */
: "=a" (lo64),
"=d" (hi64)
: "c" (shift)
: "cc");
return lo64;
}
/*
* Using the 3-argument form of the shrdq instruction (i.e. with %cl explicit),
* clang correctly generates the following __asm__() directive as written.
*/
unsigned long long
goodshift(unsigned long long lo64,
unsigned long long hi64,
unsigned char shift)
{
__asm__("shrdq %2, %1, %0" /* OK => shrdq %cl,%rdx,%rax */
: "=a" (lo64),
"=d" (hi64)
: "c" (shift)
: "cc");
return lo64;
}
--
Configure bugmail: http://llvm.org/bugs/userprefs.cgi?tab=email
------- You are receiving this mail because: -------
You are on the CC list for the bug.
_______________________________________________
LLVMbugs mailing list
[email protected]
http://lists.cs.uiuc.edu/mailman/listinfo/llvmbugs
