x86inc: Support arbitrary stack alignments

Change ALLOC_STACK to always align the stack before allocating stack space for
consistency. Previously alignment would occur either before or after allocating
stack space depending on whether manual alignment was required or not.

1 files changed, 40 insertions, 22 deletions

diff --git a/libavutil/x86/x86inc.asm b/libavutil/x86/x86inc.asm
index 28a2d87f8f..f9ef3017e3 100644
--- a/libavutil/x86/x86inc.asm
+++ b/libavutil/x86/x86inc.asm
@@ -42,6 +42,17 @@
     %define public_prefix private_prefix
 %endif
 
+%if HAVE_ALIGNED_STACK
+    %define STACK_ALIGNMENT 16
+%endif
+%ifndef STACK_ALIGNMENT
+    %if ARCH_X86_64
+        %define STACK_ALIGNMENT 16
+    %else
+        %define STACK_ALIGNMENT 4
+    %endif
+%endif
+
 %define WIN64  0
 %define UNIX64 0
 %if ARCH_X86_64
@@ -117,8 +128,9 @@
 ; %1 = number of arguments. loads them from stack if needed.
 ; %2 = number of registers used. pushes callee-saved regs if needed.
 ; %3 = number of xmm registers used. pushes callee-saved xmm regs if needed.
-; %4 = (optional) stack size to be allocated. If not aligned (x86-32 ICC 10.x,
-;      MSVC or YMM), the stack will be manually aligned (to 16 or 32 bytes),
+; %4 = (optional) stack size to be allocated. The stack will be aligned before
+;      allocating the specified stack size. If the required stack alignment is
+;      larger than the known stack alignment the stack will be manually aligned
 ;      and an extra register will be allocated to hold the original stack
 ;      pointer (to not invalidate r0m etc.). To prevent the use of an extra
 ;      register as stack pointer, request a negative stack size.
@@ -126,8 +138,10 @@
 ; PROLOGUE can also be invoked by adding the same options to cglobal
 
 ; e.g.
-; cglobal foo, 2,3,0, dst, src, tmp
-; declares a function (foo), taking two args (dst and src) and one local variable (tmp)
+; cglobal foo, 2,3,7,0x40, dst, src, tmp
+; declares a function (foo) that automatically loads two arguments (dst and
+; src) into registers, uses one additional register (tmp) plus 7 vector
+; registers (m0-m6) and allocates 0x40 bytes of stack space.
 
 ; TODO Some functions can use some args directly from the stack. If they're the
 ; last args then you can just not declare them, but if they're in the middle
@@ -328,26 +342,28 @@ DECLARE_REG_TMP_SIZE 0,1,2,3,4,5,6,7,8,9,10,11,12,13,14
     %assign n_arg_names %0
 %endmacro
 
+%define required_stack_alignment ((mmsize + 15) & ~15)
+
 %macro ALLOC_STACK 1-2 0 ; stack_size, n_xmm_regs (for win64 only)
     %ifnum %1
         %if %1 != 0
-            %assign %%stack_alignment ((mmsize + 15) & ~15)
+            %assign %%pad 0
             %assign stack_size %1
             %if stack_size < 0
                 %assign stack_size -stack_size
             %endif
-            %assign stack_size_padded stack_size
             %if WIN64
-                %assign stack_size_padded stack_size_padded + 32 ; reserve 32 bytes for shadow space
+                %assign %%pad %%pad + 32 ; shadow space
                 %if mmsize != 8
                     %assign xmm_regs_used %2
                     %if xmm_regs_used > 8
-                        %assign stack_size_padded stack_size_padded + (xmm_regs_used-8)*16
+                        %assign %%pad %%pad + (xmm_regs_used-8)*16 ; callee-saved xmm registers
                     %endif
                 %endif
             %endif
-            %if mmsize <= 16 && HAVE_ALIGNED_STACK
-                %assign stack_size_padded stack_size_padded + %%stack_alignment - gprsize - (stack_offset & (%%stack_alignment - 1))
+            %if required_stack_alignment <= STACK_ALIGNMENT
+                ; maintain the current stack alignment
+                %assign stack_size_padded stack_size + %%pad + ((-%%pad-stack_offset-gprsize) & (STACK_ALIGNMENT-1))
                 SUB rsp, stack_size_padded
             %else
                 %assign %%reg_num (regs_used - 1)
@@ -356,17 +372,17 @@ DECLARE_REG_TMP_SIZE 0,1,2,3,4,5,6,7,8,9,10,11,12,13,14
                 ; it, i.e. in [rsp+stack_size_padded], so we can restore the
                 ; stack in a single instruction (i.e. mov rsp, rstk or mov
                 ; rsp, [rsp+stack_size_padded])
-                mov  rstk, rsp
                 %if %1 < 0 ; need to store rsp on stack
-                    sub  rsp, gprsize+stack_size_padded
-                    and  rsp, ~(%%stack_alignment-1)
-                    %xdefine rstkm [rsp+stack_size_padded]
-                    mov rstkm, rstk
+                    %xdefine rstkm [rsp + stack_size + %%pad]
+                    %assign %%pad %%pad + gprsize
                 %else ; can keep rsp in rstk during whole function
-                    sub  rsp, stack_size_padded
-                    and  rsp, ~(%%stack_alignment-1)
                     %xdefine rstkm rstk
                 %endif
+                %assign stack_size_padded stack_size + ((%%pad + required_stack_alignment-1) & ~(required_stack_alignment-1))
+                mov rstk, rsp
+                and rsp, ~(required_stack_alignment-1)
+                sub rsp, stack_size_padded
+                movifnidn rstkm, rstk
             %endif
             WIN64_PUSH_XMM
         %endif
@@ -375,7 +391,7 @@ DECLARE_REG_TMP_SIZE 0,1,2,3,4,5,6,7,8,9,10,11,12,13,14
 
 %macro SETUP_STACK_POINTER 1
     %ifnum %1
-        %if %1 != 0 && (HAVE_ALIGNED_STACK == 0 || mmsize == 32)
+        %if %1 != 0 && required_stack_alignment > STACK_ALIGNMENT
             %if %1 > 0
                 %assign regs_used (regs_used + 1)
             %elif ARCH_X86_64 && regs_used == num_args && num_args <= 4 + UNIX64 * 2
@@ -449,7 +465,9 @@ DECLARE_REG 14, R15, 120
     %assign xmm_regs_used %1
     ASSERT xmm_regs_used <= 16
     %if xmm_regs_used > 8
-        %assign stack_size_padded (xmm_regs_used-8)*16 + (~stack_offset&8) + 32
+        ; Allocate stack space for callee-saved xmm registers plus shadow space and align the stack.
+        %assign %%pad (xmm_regs_used-8)*16 + 32
+        %assign stack_size_padded %%pad + ((-%%pad-stack_offset-gprsize) & (STACK_ALIGNMENT-1))
         SUB rsp, stack_size_padded
     %endif
     WIN64_PUSH_XMM
@@ -465,7 +483,7 @@ DECLARE_REG 14, R15, 120
         %endrep
     %endif
     %if stack_size_padded > 0
-        %if stack_size > 0 && (mmsize == 32 || HAVE_ALIGNED_STACK == 0)
+        %if stack_size > 0 && required_stack_alignment > STACK_ALIGNMENT
             mov rsp, rstkm
         %else
             add %1, stack_size_padded
@@ -531,7 +549,7 @@ DECLARE_REG 14, R15, 72
 
 %macro RET 0
 %if stack_size_padded > 0
-%if mmsize == 32 || HAVE_ALIGNED_STACK == 0
+%if required_stack_alignment > STACK_ALIGNMENT
     mov rsp, rstkm
 %else
     add rsp, stack_size_padded
@@ -587,7 +605,7 @@ DECLARE_ARG 7, 8, 9, 10, 11, 12, 13, 14
 
 %macro RET 0
 %if stack_size_padded > 0
-%if mmsize == 32 || HAVE_ALIGNED_STACK == 0
+%if required_stack_alignment > STACK_ALIGNMENT
     mov rsp, rstkm
 %else
     add rsp, stack_size_padded