http://llvm.org/bugs/show_bug.cgi?id=6539
Summary: x86 asm earlyclobber not respected
Product: libraries
Version: trunk
Platform: All
OS/Version: All
Status: NEW
Severity: normal
Priority: P
Component: Register Allocator
AssignedTo: [email protected]
ReportedBy: [email protected]
CC: [email protected]
Created an attachment (id=4422)
--> (http://llvm.org/bugs/attachment.cgi?id=4422)
unminimized source
Using checker-236 and
> ~/checker-236/bin/clang -O3 -mdynamic-no-pic -m32 -fomit-frame-pointer -S
> cabac_residual.i
the first inline asm compiled has its first input and output both assigned to
eax:
_decode_cabac_residual_internal:
...
LBB1_6:
...
## InlineAsm Start
movl 4(%edi), %esi
movl 0(%edi), %ebx
movzbl (%eax) , %eax
This is compiled from:
static inline int get_cabac_inline(CABACContext *c, uint8_t *const state) {
int bit;
asm volatile (
"movl 4(%2), %%esi \n\t"
"movl 0(%2), %%ebx \n\t"
"movzbl (%1) , %0 \n\t"
...
: "=&a" (bit) : "r" (state), "r" (c) : "%ecx", "%ebx", "%edx", "%esi",
"memory");
bit is an earlyclobber, so it should be assigned eax and nothing else should.
This only seems to happen when inlined, so I was unable to minimize it very
far.
This causes ffmpeg (and therefore anything else including it) to miscompile and
crash on x86-32 in the H.264 decoder.
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