[PATCH] Fix REE for vector modes (PR rtl-optimization/64286)

[Jakub Jelinek <jakub@redhat.com>]

Hi!

As mentioned in the PR, giving up for all vector mode extensions
is unnecessary, but unlike scalar integer extensions, where the low part
of the extended value is the original value, for vectors this is not true,
thus the old value is lost.  Which means we can perform REE, but only if
all uses of the definition are the same (code+mode) extension.

Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?

2015-01-12  Jakub Jelinek  <jakub@redhat.com>

	PR rtl-optimization/64286
	* ree.c (add_removable_extension): Don't add vector mode
	extensions if all uses of the source register aren't the same
	vector extensions.

	* gcc.target/i386/avx2-pr64286.c: New test.

--- gcc/ree.c.jj	2015-01-09 22:00:00.427660442 +0100
+++ gcc/ree.c	2015-01-12 12:15:56.097184674 +0100
@@ -1027,6 +1027,7 @@ add_removable_extension (const_rtx expr,
 	 different extension.  FIXME: this obviously can be improved.  */
       for (def = defs; def; def = def->next)
 	if ((idx = def_map[INSN_UID (DF_REF_INSN (def->ref))])
+	    && idx != -1U
 	    && (cand = &(*insn_list)[idx - 1])
 	    && cand->code != code)
 	  {
@@ -1038,6 +1039,57 @@ add_removable_extension (const_rtx expr,
 	      }
 	    return;
 	  }
+	/* For vector mode extensions, ensure that all uses of the
+	   XEXP (src, 0) register are the same extension (both code
+	   and to which mode), as unlike integral extensions lowpart
+	   subreg of the sign/zero extended register are not equal
+	   to the original register, so we have to change all uses or
+	   none.  */
+	else if (VECTOR_MODE_P (GET_MODE (XEXP (src, 0))))
+	  {
+	    if (idx == 0)
+	      {
+		struct df_link *ref_chain, *ref_link;
+
+		ref_chain = DF_REF_CHAIN (def->ref);
+		for (ref_link = ref_chain; ref_link; ref_link = ref_link->next)
+		  {
+		    if (ref_link->ref == NULL
+			|| DF_REF_INSN_INFO (ref_link->ref) == NULL)
+		      {
+			idx = -1U;
+			break;
+		      }
+		    rtx_insn *use_insn = DF_REF_INSN (ref_link->ref);
+		    const_rtx use_set;
+		    if (use_insn == insn || DEBUG_INSN_P (use_insn))
+		      continue;
+		    if (!(use_set = single_set (use_insn))
+			|| !REG_P (SET_DEST (use_set))
+			|| GET_MODE (SET_DEST (use_set)) != GET_MODE (dest)
+			|| GET_CODE (SET_SRC (use_set)) != code
+			|| !rtx_equal_p (XEXP (SET_SRC (use_set), 0),
+					 XEXP (src, 0)))
+		      {
+			idx = -1U;
+			break;
+		      }
+		  }
+		if (idx == -1U)
+		  def_map[INSN_UID (DF_REF_INSN (def->ref))] = idx;
+	      }
+	    if (idx == -1U)
+	      {
+		if (dump_file)
+		  {
+		    fprintf (dump_file, "Cannot eliminate extension:\n");
+		    print_rtl_single (dump_file, insn);
+		    fprintf (dump_file,
+			     " because some vector uses aren't extension\n");
+		  }
+		return;
+	      }
+	  }
 
       /* Then add the candidate to the list and insert the reaching definitions
          into the definition map.  */
--- gcc/testsuite/gcc.target/i386/avx2-pr64286.c.jj	2015-01-12 12:19:54.863031657 +0100
+++ gcc/testsuite/gcc.target/i386/avx2-pr64286.c	2015-01-12 12:19:36.000000000 +0100
@@ -0,0 +1,37 @@
+/* PR rtl-optimization/64286 */
+/* { dg-do run } */
+/* { dg-options "-O2 -mavx2" } */
+/* { dg-require-effective-target avx2 } */
+
+#include <string.h>
+#include <stdlib.h>
+#include <x86intrin.h>
+#include "avx2-check.h"
+
+__m128i v;
+__m256i w;
+
+__attribute__((noinline, noclone)) void
+foo (__m128i *p, __m128i *q)
+{
+  __m128i a = _mm_loadu_si128 (p);
+  __m128i b = _mm_xor_si128 (a, v);
+  w = _mm256_cvtepu8_epi16 (a);
+  *q = b;
+}
+
+static void
+avx2_test (void)
+{
+  v = _mm_set1_epi8 (0x40);
+  __m128i c = _mm_set_epi8 (16, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1);
+  __m128i d;
+  foo (&c, &d);
+  __m128i e = _mm_set_epi8 (0x50, 0x4f, 0x4e, 0x4d, 0x4c, 0x4b, 0x4a, 0x49,
+			    0x48, 0x47, 0x46, 0x45, 0x44, 0x43, 0x42, 0x41);
+  __m256i f = _mm256_set_epi16 (16, 15, 14, 13, 12, 11, 10, 9,
+				8, 7, 6, 5, 4, 3, 2, 1);
+  if (memcmp (&w, &f, sizeof (w)) != 0
+      || memcmp (&d, &e, sizeof (d)) != 0)
+    abort ();
+}

	Jakub