[PATCH, PR target/69454] Disable TARGET_STV when stack is not properly aligned

[Ilya Enkovich]

Hi,

Currently STV pass may require a stack realignment if any
transformation occurs to enable SSE registers spill/fill.
It appears it's invalid to increase stack alignment requirements
at this point.  Thus we have to either assume we need stack to be
aligned if are going to run STV pass or disable STV if stack is
not properly aligned.  I suppose we shouldn't ignore explicitly
requested stack alignment not beeing sure we really optimize
anything (and STV is not an optimization frequiently applied).
So I think we may disable TARGET_STV for such cases as Jakub
suggested.  This patch was bootstrapped and regtested on
x86_64-pc-linux-gnu.  OK for trunk?

Thanks,
Ilya
--
gcc/

2016-01-27  Jakub Jelinek  <ja...@redhat.com>
            Ilya Enkovich  <enkovich....@gmail.com>

        PR target/69454
        * config/i386/i386.c (convert_scalars_to_vector): Remove
        stack alignment fixes.
        (ix86_option_override_internal): Disable TARGET_STV if stack
        is not properly aligned.

gcc/testsuite/

2016-01-27  Ilya Enkovich  <enkovich....@gmail.com>

        PR target/69454
        * gcc.target/i386/pr69454-1.c: New test.
        * gcc.target/i386/pr69454-2.c: New test.


diff --git a/gcc/config/i386/i386.c b/gcc/config/i386/i386.c
index 34b57a4..9fb8db8 100644
--- a/gcc/config/i386/i386.c
+++ b/gcc/config/i386/i386.c
@@ -3588,16 +3588,6 @@ convert_scalars_to_vector ()
   bitmap_obstack_release (NULL);
   df_process_deferred_rescans ();
 
-  /* Conversion means we may have 128bit register spills/fills
-     which require aligned stack.  */
-  if (converted_insns)
-    {
-      if (crtl->stack_alignment_needed < 128)
-       crtl->stack_alignment_needed = 128;
-      if (crtl->stack_alignment_estimated < 128)
-       crtl->stack_alignment_estimated = 128;
-    }
-
   return 0;
 }
 
@@ -5453,6 +5443,11 @@ ix86_option_override_internal (bool main_args_p,
     opts->x_target_flags |= MASK_VZEROUPPER;
   if (!(opts_set->x_target_flags & MASK_STV))
     opts->x_target_flags |= MASK_STV;
+  /* Disable STV if -mpreferred-stack-boundary={2,3} - the needed
+     stack realignment will be extra cost the pass doesn't take into
+     account and the pass can't realign the stack.  */
+  if (ix86_preferred_stack_boundary < 64)
+    opts->x_target_flags &= ~MASK_STV;
   if (!ix86_tune_features[X86_TUNE_AVX256_UNALIGNED_LOAD_OPTIMAL]
       && !(opts_set->x_target_flags & MASK_AVX256_SPLIT_UNALIGNED_LOAD))
     opts->x_target_flags |= MASK_AVX256_SPLIT_UNALIGNED_LOAD;
diff --git a/gcc/testsuite/gcc.target/i386/pr69454-1.c 
b/gcc/testsuite/gcc.target/i386/pr69454-1.c
new file mode 100644
index 0000000..12ecfd3
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/pr69454-1.c
@@ -0,0 +1,11 @@
+/* { dg-do compile { target { ia32 } } } */
+/* { dg-options "-O2 -msse2 -mno-accumulate-outgoing-args 
-mpreferred-stack-boundary=2" } */
+
+typedef struct { long long w64[2]; } V128;
+extern V128* fn2(void);
+long long a;
+V128 b;
+void fn1() {
+  V128 *c = fn2();
+  c->w64[0] = a ^ b.w64[0];
+}
diff --git a/gcc/testsuite/gcc.target/i386/pr69454-2.c 
b/gcc/testsuite/gcc.target/i386/pr69454-2.c
new file mode 100644
index 0000000..28bab93
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/pr69454-2.c
@@ -0,0 +1,13 @@
+/* { dg-do compile { target { ia32 } } } */
+/* { dg-options "-O2 -mpreferred-stack-boundary=2" } */
+
+extern void fn2 ();
+long long a, b;
+
+void fn1 ()
+{
+  long long c = a;
+  a = b ^ a;
+  fn2 ();
+  a = c;
+}