x86: replace explicit REP_RETs with RETs

From x86inc:
> On AMD cpus <=K10, an ordinary ret is slow if it immediately follows either
> a branch or a branch target. So switch to a 2-byte form of ret in that case.
> We can automatically detect "follows a branch", but not a branch target.
> (SSSE3 is a sufficient condition to know that your cpu doesn't have this problem.)

x86inc can automatically determine whether to use REP_RET rather than
REP in most of these cases, so impact is minimal. Additionally, a few
REP_RETs were used unnecessary, despite the return being nowhere near a
branch.

The only CPUs affected were AMD K10s, made between 2007 and 2011, 16
years ago and 12 years ago, respectively.

In the future, everyone involved with x86inc should consider dropping
REP_RETs altogether.

libavutil/x86/float_dsp.asm

@@ -48,7 +48,7 @@ ALIGN 16
 
     sub       lenq, 64
     jge       .loop
-    REP_RET
+    RET
 %endmacro
 
 INIT_XMM sse
@@ -141,7 +141,7 @@ cglobal vector_fmac_scalar, 4,4,5, dst, src, mul, len
 %endif ; mmsize
     sub    lenq, 64
     jge .loop
-    REP_RET
+    RET
 %endmacro
 
 INIT_XMM sse
@@ -178,7 +178,7 @@ cglobal vector_fmul_scalar, 4,4,3, dst, src, mul, len
     mova  [dstq+lenq], m1
     sub    lenq, mmsize
     jge .loop
-    REP_RET
+    RET
 %endmacro
 
 INIT_XMM sse
@@ -233,7 +233,7 @@ cglobal vector_dmac_scalar, 4,4,5, dst, src, mul, len
     movaps [dstq+lenq+3*mmsize], m4
     sub    lenq, mmsize*4
     jge .loop
-    REP_RET
+    RET
 %endmacro
 
 INIT_XMM sse2
@@ -280,7 +280,7 @@ cglobal vector_dmul_scalar, 4,4,3, dst, src, mul, len
     movaps [dstq+lenq+mmsize], m2
     sub          lenq, 2*mmsize
     jge .loop
-    REP_RET
+    RET
 %endmacro
 
 INIT_XMM sse2
@@ -323,7 +323,7 @@ cglobal vector_fmul_window, 5, 6, 6, dst, src0, src1, win, len, len1
     sub       len1q, mmsize
     add       lenq,  mmsize
     jl .loop
-    REP_RET
+    RET
 
 ;-----------------------------------------------------------------------------
 ; vector_fmul_add(float *dst, const float *src0, const float *src1,
@@ -352,7 +352,7 @@ ALIGN 16
 
     sub     lenq,   2*mmsize
     jge     .loop
-    REP_RET
+    RET
 %endmacro
 
 INIT_XMM sse
@@ -401,7 +401,7 @@ ALIGN 16
     add     src1q, 2*mmsize
     sub     lenq,  2*mmsize
     jge     .loop
-    REP_RET
+    RET
 %endmacro
 
 INIT_XMM sse
@@ -585,4 +585,4 @@ cglobal butterflies_float, 3,3,3, src0, src1, len
     mova        [src0q + lenq], m0
     add       lenq, mmsize
     jl .loop
-    REP_RET
+    RET