[LLVMbugs] [Bug 5599] New: clang doesn't follow x86-64 ABI array alignment rule

bugzilla-daemon at cs.uiuc.edu bugzilla-daemon at cs.uiuc.edu
Mon Nov 23 10:49:16 PST 2009


           Summary: clang doesn't follow x86-64 ABI array alignment rule
           Product: clang
           Version: trunk
          Platform: PC
        OS/Version: All
            Status: NEW
          Severity: normal
          Priority: P2
         Component: LLVM Codegen
        AssignedTo: unassignedclangbugs at nondot.org
        ReportedBy: gohman at apple.com
                CC: llvmbugs at cs.uiuc.edu

The x86-64 ABI, in section 3.1.2 Data Representation, subsection "Aggregates
and Unions", second paragraph, says:

"An array uses the same alignment as its elements, except that a local or
global array variable of length at least 16 bytes or a C99 variable-length
variable always has alignment of at least 16 bytes."

For the following testcase:

void frob(void *);

void foo(void) {
  float x[4];

clang -O2 -emit-llvm -m64 emits

  %x = alloca [4 x float], align 4                ; <[4 x float]*> [#uses=1]

which shows that the array is not being aligned on a 16 byte boundary.

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.

More information about the llvm-bugs mailing list