tree-optimization/79333 - fold stmts following SSA edges in VN

This makes sure to follow SSA edges when folding eliminated stmts.
This reaps the same benefit as forwprop folding all stmts, not
waiting for one to produce copysign in the new testcase.

2021-05-04  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/79333
	* tree-ssa-sccvn.c (eliminate_dom_walker::eliminate_stmt):
	Fold stmt following SSA edges.

	* gcc.dg/tree-ssa/ssa-fre-94.c: New testcase.
	* gcc.dg/graphite/fuse-1.c: Adjust.
	* gcc.dg/pr43864-4.c: Likewise.

gcc/testsuite/gcc.dg/graphite/fuse-1.c

@@ -1,6 +1,6 @@
 /* Check that the two loops are fused and that we manage to fold the two xor
    operations.  */
-/* { dg-options "-O2 -floop-nest-optimize -fdump-tree-forwprop-all -fdump-tree-graphite-all" } */
+/* { dg-options "-O2 -floop-nest-optimize -fdump-tree-forwprop4 -fdump-tree-graphite-all" } */
 
 /* Make sure we fuse the loops like this:
 AST generated by isl:
@@ -12,7 +12,7 @@ for (int c0 = 0; c0 <= 99; c0 += 1) {
 /* { dg-final { scan-tree-dump-times "AST generated by isl:.*for \\(int c0 = 0; c0 <= 99; c0 \\+= 1\\) \\{.*S_.*\\(c0\\);.*S_.*\\(c0\\);.*S_.*\\(c0\\);.*\\}" 1 "graphite" } } */
 
 /* Check that after fusing the loops, the scalar computation is also fused.  */
-/* { dg-final { scan-tree-dump-times "gimple_simplified to\[^\\n\]*\\^ 12" 1 "forwprop4" } } */
+/* { dg-final { scan-tree-dump-times " \\^ 12;" 2 "forwprop4" } } */
 
 #define MAX 100
 int A[MAX];

gcc/testsuite/gcc.dg/pr43864-4.c

@@ -22,7 +22,7 @@ int f(int c, int b, int d)
   return r - r2;
 }
 
-/* { dg-final { scan-tree-dump-times "if " 0 "pre"} } */
-/* { dg-final { scan-tree-dump-times "(?n)_.*\\+.*_" 1 "pre"} } */
-/* { dg-final { scan-tree-dump-times "(?n)_.*-.*_" 2 "pre"} } */
+/* During PRE elimination we should simplify this to return b * 2.  */
+/* { dg-final { scan-tree-dump-times "if " 0 "pre" } } */
+/* { dg-final { scan-tree-dump "_\[0-9\]+ = b_\[0-9\]+\\(D\\) \\* 2;\[\\r\\n\]\[^\\r\\n\]*return _\[0-9\]+;" "pre" } } */
 /* { dg-final { scan-tree-dump-not "Invalid sum" "pre"} } */

gcc/testsuite/gcc.dg/tree-ssa/ssa-fre-94.c

@@ -0,0 +1,16 @@
+/* PR tree-optimization/79333 */
+/* { dg-do compile } */
+/* { dg-options "-O -ffinite-math-only -fdump-tree-fre1" } */
+
+extern __inline __attribute__ ((__always_inline__,__gnu_inline__))
+double __attribute__ ((__nothrow__ , __leaf__))
+fabs (double __x) { return __builtin_fabs (__x); }
+
+double f(float f)
+{
+  double t1 = fabs(f);
+  double t2 = f / t1;
+  return t2;
+}
+
+/* { dg-final { scan-tree-dump "copysign" "fre1" } } */

gcc/tree-ssa-sccvn.c

@@ -6362,7 +6362,7 @@ eliminate_dom_walker::eliminate_stmt (basic_block b, gimple_stmt_iterator *gsi)
 	recompute_tree_invariant_for_addr_expr (gimple_assign_rhs1 (stmt));
       gimple_stmt_iterator prev = *gsi;
       gsi_prev (&prev);
-      if (fold_stmt (gsi))
+      if (fold_stmt (gsi, follow_all_ssa_edges))
 	{
 	  /* fold_stmt may have created new stmts inbetween
 	     the previous stmt and the folded stmt.  Mark