tree-optimization/92819 restrict new vector CTOR canonicalization

The PR shows that code generation ends up pessimized by the new
canonicalization rules that end up nailing do-not-care elements
to specific values making it hard to generate good code later.

The temporary solution is to avoid this for the cases we also
obviously know the canonicalization will create more GIMPLE stmts than
before.

2020-02-04  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/92819
	* tree-ssa-forwprop.c (simplify_vector_constructor): Avoid
	generating more stmts than before.

	* gcc.target/i386/pr92819.c: New testcase.
	* gcc.target/i386/pr92803.c: Adjust.

5 files changed, 73 insertions, 4 deletions

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 59d606b..4a5dddb 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,9 @@
+2020-02-04  Richard Biener  <rguenther@suse.de>
+
+	PR tree-optimization/92819
+	* tree-ssa-forwprop.c (simplify_vector_constructor): Avoid
+	generating more stmts than before.
+
 2020-02-04  Martin Liska  <mliska@suse.cz>
 
 	* config/arm/arm.c (arm_gen_far_branch): Move the function
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index 28ecbe1..1624f59 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,9 @@
+2020-02-04  Richard Biener  <rguenther@suse.de>
+
+	PR tree-optimization/92819
+	* gcc.target/i386/pr92819.c: New testcase.
+	* gcc.target/i386/pr92803.c: Adjust.
+
 2020-02-03  Iain Sandoe  <iain@sandoe.co.uk>
 
 	PR c++/93458
diff --git a/gcc/testsuite/gcc.target/i386/pr92803.c b/gcc/testsuite/gcc.target/i386/pr92803.c
index d533bae..6d4c07a 100644
--- a/gcc/testsuite/gcc.target/i386/pr92803.c
+++ b/gcc/testsuite/gcc.target/i386/pr92803.c
@@ -36,5 +36,6 @@ barf (v8sf x)
 /* We expect all other CTORs to turn into permutes, the FP converting ones
    to two each with the one with constants possibly elided in the future
    by converting 3.0f and 1.0f "back" to integers.  */
-/* { dg-final { scan-tree-dump-times "VEC_PERM_EXPR" 4 "forwprop1" } } */
-/* { dg-final { scan-tree-dump-times "VEC_PERM_EXPR" 3 "forwprop1" { xfail *-*-* } } } */
+/* For foo we do nothing.  */
+/* { dg-final { scan-tree-dump-times "VEC_PERM_EXPR" 3 "forwprop1" } } */
+/* { dg-final { scan-tree-dump-times "VEC_PERM_EXPR" 2 "forwprop1" { xfail *-*-* } } } */
diff --git a/gcc/testsuite/gcc.target/i386/pr92819.c b/gcc/testsuite/gcc.target/i386/pr92819.c
new file mode 100644
index 0000000..773e349
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/pr92819.c
@@ -0,0 +1,45 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -mavx2 -fdump-tree-forwprop1" } */
+
+typedef double v4df __attribute__((vector_size (32)));
+typedef double v2df __attribute__((vector_size (16)));
+typedef short v16hi __attribute__((vector_size (32)));
+typedef short v8hi __attribute__((vector_size (16)));
+
+v2df
+foo (v4df x, double *p)
+{
+  return (v2df) { x[1], *p };
+}
+
+v2df
+bar (v4df x, double *p)
+{
+  return (v2df) { x[0], *p }; /* BIT_INSERT_EXPR */
+}
+
+v2df
+baz (v2df x, double *p)
+{
+  return (v2df) { x[1], *p }; /* VEC_PERM_EXPR */
+}
+
+v2df
+qux (v2df x, double *p)
+{
+  return (v2df) { x[0], *p }; /* BIT_INSERT_EXPR */
+}
+
+v2df
+corge (v4df x, double *p)
+{
+  return (v2df) { x[3], *p };
+}
+
+/* { dg-final { scan-tree-dump-times "BIT_INSERT_EXPR" 2 "forwprop1" } } */
+/* { dg-final { scan-tree-dump-times "VEC_PERM_EXPR" 1 "forwprop1" } } */
+/* We can't check for 1:1 assembler here so check for what we do not
+   want to see.  */
+/* { dg-final { scan-assembler-not { "perm" } } } */
+/* { dg-final { scan-assembler-not { "insert" } } } */
+/* { dg-final { scan-assembler-not { "broadcast" } } } */
diff --git a/gcc/tree-ssa-forwprop.c b/gcc/tree-ssa-forwprop.c
index 5203891..f65216d 100644
--- a/gcc/tree-ssa-forwprop.c
+++ b/gcc/tree-ssa-forwprop.c
@@ -2230,7 +2230,6 @@ simplify_vector_constructor (gimple_stmt_iterator *gsi)
   unsigned HOST_WIDE_INT refnelts;
   enum tree_code conv_code;
   constructor_elt *elt;
-  bool maybe_ident;
 
   op = gimple_assign_rhs1 (stmt);
   type = TREE_TYPE (op);
@@ -2245,7 +2244,8 @@ simplify_vector_constructor (gimple_stmt_iterator *gsi)
   orig[0] = NULL;
   orig[1] = NULL;
   conv_code = ERROR_MARK;
-  maybe_ident = true;
+  bool maybe_ident = true;
+  bool maybe_blend[2] = { true, true };
   tree one_constant = NULL_TREE;
   tree one_nonconstant = NULL_TREE;
   auto_vec<tree> constants;
@@ -2290,6 +2290,8 @@ simplify_vector_constructor (gimple_stmt_iterator *gsi)
 	      orig[j] = ref;
 	      if (elem != i || j != 0)
 		maybe_ident = false;
+	      if (elem != i)
+		maybe_blend[j] = false;
 	      elts.safe_push (std::make_pair (j, elem));
 	      continue;
 	    }
@@ -2439,6 +2441,15 @@ simplify_vector_constructor (gimple_stmt_iterator *gsi)
     }
   else
     {
+      /* If we combine a vector with a non-vector avoid cases where
+	 we'll obviously end up with more GIMPLE stmts which is when
+	 we'll later not fold this to a single insert into the vector
+	 and we had a single extract originally.  See PR92819.  */
+      if (nelts == 2
+	  && refnelts > 2
+	  && orig[1] == error_mark_node
+	  && !maybe_blend[0])
+	return false;
       tree mask_type, perm_type, conv_src_type;
       perm_type = TREE_TYPE (orig[0]);
       conv_src_type = (nelts == refnelts