[Pixman] [PATCH 2/3] ARMv6: Support for very variable-hungry composite operations

[Pekka Paalanen]

From: Ben Avison <bavison at riscosopen.org>

Previously, the variable ARGS_STACK_OFFSET was available to extract values
from function arguments during the init macro. Now this changes dynamically
around stack operations in the function as a whole so that arguments can be
accessed at any point. It is also joined by LOCALS_STACK_OFFSET, which
allows access to space reserved on the stack during the init macro.

On top of this, composite macros now have the option of using all of WK0-WK3
registers rather than just the subset it was told to use; this requires the
pixel count to be spilled to the stack over the leading pixels at the start
of each line. Thus, at best, each composite operation can use 11 registers,
plus any pointer registers not required for the composite type, plus as much
stack space as it needs, divided up into constants and variables as necessary.
---
 pixman/pixman-arm-simd-asm.h | 56 +++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 53 insertions(+), 3 deletions(-)

diff --git a/pixman/pixman-arm-simd-asm.h b/pixman/pixman-arm-simd-asm.h
index 24b1ad2..852a113 100644
--- a/pixman/pixman-arm-simd-asm.h
+++ b/pixman/pixman-arm-simd-asm.h
@@ -76,6 +76,8 @@
 .set FLAG_SPILL_LINE_VARS,           48
 .set FLAG_PROCESS_CORRUPTS_SCRATCH,  0
 .set FLAG_PROCESS_PRESERVES_SCRATCH, 64
+.set FLAG_PROCESS_PRESERVES_WK0,     0
+.set FLAG_PROCESS_CORRUPTS_WK0,      128 /* if possible, use the specified register(s) instead so WK0 can hold number of leading pixels */
 
 /*
  * Offset into stack where mask and source pointer/stride can be accessed.
@@ -87,6 +89,11 @@
 #endif
 
 /*
+ * Offset into stack where space allocated during init macro can be accessed.
+ */
+.set LOCALS_STACK_OFFSET,     0
+
+/*
  * Constants for selecting preferable prefetch type.
  */
 .set PREFETCH_TYPE_NONE,       0
@@ -359,23 +366,41 @@
 
 
 .macro test_bits_1_0_ptr
+ .if (flags) & FLAG_PROCESS_CORRUPTS_WK0
+        movs    SCRATCH, X, lsl #32-1  /* C,N = bits 1,0 of DST */
+ .else
         movs    SCRATCH, WK0, lsl #32-1  /* C,N = bits 1,0 of DST */
+ .endif
 .endm
 
 .macro test_bits_3_2_ptr
+ .if (flags) & FLAG_PROCESS_CORRUPTS_WK0
+        movs    SCRATCH, X, lsl #32-3  /* C,N = bits 3, 2 of DST */
+ .else
         movs    SCRATCH, WK0, lsl #32-3  /* C,N = bits 3, 2 of DST */
+ .endif
 .endm
 
 .macro leading_15bytes  process_head, process_tail
         /* On entry, WK0 bits 0-3 = number of bytes until destination is 16-byte aligned */
+ .set DECREMENT_X, 1
+ .if (flags) & FLAG_PROCESS_CORRUPTS_WK0
+  .set DECREMENT_X, 0
+        sub     X, X, WK0, lsr #dst_bpp_shift
+        str     X, [sp, #LINE_SAVED_REG_COUNT*4]
+        mov     X, WK0
+ .endif
         /* Use unaligned loads in all cases for simplicity */
  .if dst_w_bpp == 8
-        conditional_process2  test_bits_1_0_ptr, mi, cs, process_head, process_tail, 1, 2, 1, 2, 1, 1, 1
+        conditional_process2  test_bits_1_0_ptr, mi, cs, process_head, process_tail, 1, 2, 1, 2, 1, 1, DECREMENT_X
  .elseif dst_w_bpp == 16
         test_bits_1_0_ptr
-        conditional_process1  cs, process_head, process_tail, 2, 2, 1, 1, 1
+        conditional_process1  cs, process_head, process_tail, 2, 2, 1, 1, DECREMENT_X
+ .endif
+        conditional_process2  test_bits_3_2_ptr, mi, cs, process_head, process_tail, 4, 8, 1, 2, 1, 1, DECREMENT_X
+ .if (flags) & FLAG_PROCESS_CORRUPTS_WK0
+        ldr     X, [sp, #LINE_SAVED_REG_COUNT*4]
  .endif
-        conditional_process2  test_bits_3_2_ptr, mi, cs, process_head, process_tail, 4, 8, 1, 2, 1, 1, 1
 .endm
 
 .macro test_bits_3_2_pix
@@ -705,6 +730,13 @@ fname:
 #endif
 
         init
+
+ .if (flags) & FLAG_PROCESS_CORRUPTS_WK0
+        /* Reserve a word in which to store X during leading pixels */
+        sub     sp, sp, #4
+  .set ARGS_STACK_OFFSET, ARGS_STACK_OFFSET+4
+  .set LOCALS_STACK_OFFSET, LOCALS_STACK_OFFSET+4
+ .endif
         
         lsl     STRIDE_D, #dst_bpp_shift /* stride in bytes */
         sub     STRIDE_D, STRIDE_D, X, lsl #dst_bpp_shift
@@ -734,6 +766,8 @@ fname:
   .if (flags) & FLAG_SPILL_LINE_VARS_WIDE
         /* This is stmdb sp!,{} */
         .word   0xE92D0000 | LINE_SAVED_REGS
+   .set ARGS_STACK_OFFSET, ARGS_STACK_OFFSET + LINE_SAVED_REG_COUNT*4
+   .set LOCALS_STACK_OFFSET, LOCALS_STACK_OFFSET + LINE_SAVED_REG_COUNT*4
   .endif
 151:    /* New line */
         newline
@@ -767,6 +801,10 @@ fname:
 
 157:    /* Check for another line */
         end_of_line 1, %((flags) & FLAG_SPILL_LINE_VARS_WIDE), 151b
+  .if (flags) & FLAG_SPILL_LINE_VARS_WIDE
+   .set ARGS_STACK_OFFSET, ARGS_STACK_OFFSET - LINE_SAVED_REG_COUNT*4
+   .set LOCALS_STACK_OFFSET, LOCALS_STACK_OFFSET - LINE_SAVED_REG_COUNT*4
+  .endif
  .endif
 
  .ltorg
@@ -776,6 +814,8 @@ fname:
  .if (flags) & FLAG_SPILL_LINE_VARS_NON_WIDE
         /* This is stmdb sp!,{} */
         .word   0xE92D0000 | LINE_SAVED_REGS
+  .set ARGS_STACK_OFFSET, ARGS_STACK_OFFSET + LINE_SAVED_REG_COUNT*4
+  .set LOCALS_STACK_OFFSET, LOCALS_STACK_OFFSET + LINE_SAVED_REG_COUNT*4
  .endif
 161:    /* New line */
         newline
@@ -841,12 +881,22 @@ fname:
 
 177:    /* Check for another line */
         end_of_line %(dst_w_bpp < 32), %((flags) & FLAG_SPILL_LINE_VARS_NON_WIDE), 171b, last_one
+ .if (flags) & FLAG_SPILL_LINE_VARS_NON_WIDE
+  .set ARGS_STACK_OFFSET, ARGS_STACK_OFFSET - LINE_SAVED_REG_COUNT*4
+  .set LOCALS_STACK_OFFSET, LOCALS_STACK_OFFSET - LINE_SAVED_REG_COUNT*4
+ .endif
 
 197:
  .if (flags) & FLAG_SPILL_LINE_VARS
         add     sp, sp, #LINE_SAVED_REG_COUNT*4
  .endif
 198:
+ .if (flags) & FLAG_PROCESS_CORRUPTS_WK0
+  .set ARGS_STACK_OFFSET, ARGS_STACK_OFFSET-4
+  .set LOCALS_STACK_OFFSET, LOCALS_STACK_OFFSET-4
+        add     sp, sp, #4
+ .endif
+
         cleanup
 
 #ifdef DEBUG_PARAMS
-- 
1.8.3.2