[X86] No support for fp stack in inline asm

[llvmbot]

Bugzilla Link	879
Resolution	FIXED
Resolved on	Jun 29, 2011 01:56
Version	1.8
OS	Linux
Blocks	#1234 llvm/llvm-bugzilla-archive#3696 llvm/llvm-bugzilla-archive#4434
Reporter	LLVM Bugzilla Contributor
CC	@asl,@DimitryAndric,@EdSchouten,@nlewycky,@pwo,@stoklund

Extended Description

Hi there,

I was compiling lame-3.95.1 with the new tar file llvm-1.8a.tar.gz and
llvm-gcc4-1.8-source on Fedora Core 5. I wanted to check some timings for .wav
to .mp3 encoding.

The lame package compiles fine using llvm-gcc and -O0 but it dies using -O3
(which is the default opt level in the makefile). Gcc 4.0.3 works fine with all
opt levels. Llvm-gcc dies on all opt levels, except -0O.

The compilation goes through the mpglib subdirectory fine but it dies in the
libmp3lame subdirectory with the following:

snip....
llvm-gcc -DHAVE_CONFIG_H -I. -I. -I.. -I../include -I. -I../mpglib/ -I.. -Wall
-pipe -O3 -MT VbrTag.lo -MD -MP -MF .deps/VbrTag.Tpo -c VbrTag.c -fPIC -DPIC -o
.libs/VbrTag.o
VbrTag.c: In function 'PutLameVBR':
VbrTag.c:772: warning: pointer targets in passing argument 1 of
'__builtin_strncpy' differ in signedness
VbrTag.c: In function 'PutVbrTag':
VbrTag.c:1000: warning: pointer targets in passing argument 2 of
'CRC_writeheader' differ in signedness
cc1: SelectionDAGISel.cpp:2142: void
llvm::SelectionDAGLowering::visitInlineAsm(llvm::CallInst&): Assertion
`!Regs.Regs.empty() && "Couldn't allocate output reg!"' failed.
VbrTag.c: At top level:
VbrTag.c:1030: internal compiler error: Aborted
snip...

I don't know enough about llvm at present, to offer an intelligent guess as to
why this is happening. Sorry ;)

Lame source can be downloaded here:
http://prdownloads.sourceforge.net/lame/lame-3.95.1.tar.gz

Thanks,
Kelly

[lattner]

Can you please attach a ".i" file, generated according to these instructions:
http://llvm.org/docs/HowToSubmitABug.html#front-end

Thanks,

-Chris

[llvmbot]

Crashes llvm-gcc
A .i file of the offending VbrTag.c file.

[lattner]

Here is a reduced testcase:

double floor(double __x) {
register long double __value;
__volatile unsigned short int __cw;
__volatile unsigned short int __cwtmp;
__asm           __volatile("fnstcw %0":"=m"(__cw));
__cwtmp = (__cw & 0xf3ff) | 0x0400;
__asm           __volatile("fldcw %0"::"m"(__cwtmp));
__asm           __volatile("frndint":"=t"(__value):"0"(__x));
__asm           __volatile("fldcw %0"::"m"(__cw));
return __value;
}

Basically this boils down to the fact that we don't support "t" constraints (fp stack) in inline asms. 

Unfortunately, I don't plan to implement this support in the near future, however, as a work-around,
most linux distros allow you to compile with -D__NO_MATH_INLINES, which disables these.

-Chris

[lattner]

Here's a testcase from redhat FC5 headers:

double %intcoord(double %X) {
%tmp85 = call double asm sideeffect "frndint", "={st},0,{dirflag},{fpsr},~{flags}"( double %X)
ret double %tmp85
}

It would be good to support the simple case of this at least.

-Chris

[llvmbot]

This patch:
http://lists.cs.uiuc.edu/pipermail/llvm-commits/Week-of-Mon-20060821/037043.html
was applied to work around this problem on x86/Linux. It needs to be undone once
this bug is resolved.

[lattner]

*** Bug #1243 has been marked as a duplicate of this bug. ***

[lattner]

*** Bug llvm/llvm-bugzilla-archive#921 has been marked as a duplicate of this bug. ***

[lattner]

*** Bug llvm/llvm-bugzilla-archive#937 has been marked as a duplicate of this bug. ***

[asl]

Another simple testcase from Qt:

inline double qCos_x86(double a)
{
double r;
asm (
"fcos"
: "=t" (r) : "0" (a));
return r;
}

[lattner]

Here are some testcases:

double floor(double __x) {
double __value;
__asm ("frndint":"=t"(__value):"0"(__x));
return __value;
}

// This has two inputs and pops one.
int test(double x, double y) {

register char __result;
asm ("fucomip %%st(1), %%st; seta %%al"
: "=a" (__result) : "u" (y), "t" (x) : "cc", "st");
return __result;
}
double test2(double __x) {
double __value;
__asm volatile("fscale" : "=t" (__value) : "0" (1.0), "u" (__x));
return __value;
}

Unfortunately, this won't happen for 1.9.

-Chris

[asl]

*** Bug llvm/llvm-bugzilla-archive#1051 has been marked as a duplicate of this bug. ***

[lattner]

*** Bug llvm/llvm-bugzilla-archive#1211 has been marked as a duplicate of this bug. ***

[asl]

*** Bug llvm/llvm-bugzilla-archive#1272 has been marked as a duplicate of this bug. ***

[lattner]

akor, could you try adding something like this to i386.h:

builtin_assert("__NO_MATH_INLINES");

Somewhere in TARGET_CPU_CPP_BUILTINS. This should eliminate the worst part of this problem until we
can fix it right.

[lattner]

s/builtin_assert/builtin_define, sorry.