movw. That is we promote the destination operand to r16. So
%CH = TRUNC_R16_R8 %BP
is emitted as
movw %bp, %cx.
This is incorrect. If %cl is live, it would be clobbered.
Ideally we want to do the opposite, that is emitted it as
movb ??, %ch
But this is not possible since %bp does not have a r8 sub-register.
We are now defining a new register class R16_ which is a subclass of R16
containing only those 16-bit registers that have r8 sub-registers (i.e.
AX - DX). We isel the truncate to two instructions, a MOV16to16_ to copy the
value to the R16_ class, followed by a TRUNC_R16_R8.
Due to bug 770, the register colaescer is not going to coalesce between R16 and
R16_. That will be fixed later so we can eliminate the MOV16to16_. Right now, it
can only be eliminated if we are lucky that source and destination registers are
the same.
llvm-svn: 28164
for Darwin.
* Added lowering hook for ISD::RET. It inserts CopyToRegs for the return
value (or store / fld / copy to ST(0) for floating point value). This
eliminate the need to write C++ code to handle RET with variable number
of operands.
llvm-svn: 24888
XMM registers. There are many known deficiencies and fixmes, which will be
addressed ASAP. The major benefit of this work is that it will allow the
LLVM register allocator to allocate FP registers across basic blocks.
The x86 backend will still default to x87 style FP. To enable this work,
you must pass -enable-sse-scalar-fp and either -sse2 or -sse3 to llc.
An example before and after would be for:
double foo(double *P) { double Sum = 0; int i; for (i = 0; i < 1000; ++i)
Sum += P[i]; return Sum; }
The inner loop looks like the following:
x87:
.LBB_foo_1: # no_exit
fldl (%esp)
faddl (%eax,%ecx,8)
fstpl (%esp)
incl %ecx
cmpl $1000, %ecx
#FP_REG_KILL
jne .LBB_foo_1 # no_exit
SSE2:
addsd (%eax,%ecx,8), %xmm0
incl %ecx
cmpl $1000, %ecx
#FP_REG_KILL
jne .LBB_foo_1 # no_exit
llvm-svn: 22340
working. The instruction selector changes will hopefully be coming later
this week once they are debugged. This is necessary to support the darwin
x86 FP model, and is recommended by intel as the replacement for x87. As
a bonus, the register allocator knows how to deal with these registers
across basic blocks, unliky the FP stackifier. This leads to significantly
better codegen in several cases.
llvm-svn: 22300
1) For 8-bit registers try to use first the ones that are parts of the
same register (AL then AH). This way we only alias 2 16/32-bit
registers after allocating 4 8-bit variables.
2) Move EBX as the last register to allocate. This will cause less
spills to happen since we will have 8-bit registers available up to
register excaustion (assuming we use the allocation order). It
would be nice if we could push all of the 8-bit aliased registers
towards the end but we much prefer to keep callee saved register to
the end to avoid saving them on entry and exit of the function.
For example this gives a slight reduction of spills with linear scan
on 164.gzip.
Before:
11221 asm-printer - Number of machine instrs printed
975 spiller - Number of loads added
675 spiller - Number of stores added
398 spiller - Number of register spills
After:
11182 asm-printer - Number of machine instrs printed
952 spiller - Number of loads added
652 spiller - Number of stores added
386 spiller - Number of register spills
llvm-svn: 11996
