[gcc r12-3304] Call reduce_vector_comparison_to_scalar_comparison earlier

[gcc r12-3304] Call reduce_vector_comparison_to_scalar_comparison earlier

[Jeff Law]

https://gcc.gnu.org/g:165446a1e81f5bb9597289e783af9ee67e1fe5ba

commit r12-3304-g165446a1e81f5bb9597289e783af9ee67e1fe5ba
Author: Jeff Law <jlaw@localhost.localdomain>
Date:   Wed Sep 1 19:13:58 2021 -0400

    Call reduce_vector_comparison_to_scalar_comparison earlier
    
    As noted in the PR, we can get an ICE after the introduction of code to reduce a vector comparison to a scalar.  The problem is we left the operand cache in an inconsistent state because we called the new function too late.   This is trivially fixed by making the transformation before we call update_stmt_if_modified.
    
    The irony here is the whole point of calling reduce_vector_comparison_to_scalar_comparison when we did was to expose these kinds of secondary opportunities.  In this particular case we collapsed the test to a comparison of constants (thus no SSA operands).
    
    Anyway, this fixes the problem in the obvious way.  This may all end up being moot if I can twiddle Richi's match.pd pattern to work.  It doesn't work as-written due to a couple issues that I haven't worked totally through yet.
    
    Installed on the trunk after bootstrap & regression testing on x86 and verifying it addresses the aarch64 issue.
    
    gcc/
            PR tree-optimization/102152
            * tree-ssa-dom.c (dom_opt_dom_walker::optimize_stmt): Reduce a vector
            comparison to a scalar comparison before calling
            update_stmt_if_modified.
    
    gcc/testsuite/
            PR tree-optimization/102152
            * gcc.dg/pr102152.c: New test

Diff:
---
 gcc/testsuite/gcc.dg/pr102152.c | 14 ++++++++++++++
 gcc/tree-ssa-dom.c              |  6 +++---
 2 files changed, 17 insertions(+), 3 deletions(-)

diff --git a/gcc/testsuite/gcc.dg/pr102152.c b/gcc/testsuite/gcc.dg/pr102152.c
new file mode 100644
index 00000000000..4e0c1f5a3d5
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr102152.c
@@ -0,0 +1,14 @@
+/* { dg-do compile } */
+/* { dg-options "-O1 -ftree-loop-vectorize -fno-tree-fre" } */
+/* { dg-additional-options "-march=armv8-a+sve" { target aarch64-*-* } } */
+
+
+
+signed char i;
+
+void
+foo (void)
+{
+  for (i = 0; i < 6; i += 5)
+    ;
+}
diff --git a/gcc/tree-ssa-dom.c b/gcc/tree-ssa-dom.c
index a5245b33de6..49d8f96408f 100644
--- a/gcc/tree-ssa-dom.c
+++ b/gcc/tree-ssa-dom.c
@@ -1990,14 +1990,14 @@ dom_opt_dom_walker::optimize_stmt (basic_block bb, gimple_stmt_iterator *si,
       print_gimple_stmt (dump_file, stmt, 0, TDF_SLIM);
     }
 
-  update_stmt_if_modified (stmt);
-  opt_stats.num_stmts++;
-
   /* STMT may be a comparison of uniform vectors that we can simplify
      down to a comparison of scalars.  Do that transformation first
      so that all the scalar optimizations from here onward apply.  */
   reduce_vector_comparison_to_scalar_comparison (stmt);
 
+  update_stmt_if_modified (stmt);
+  opt_stats.num_stmts++;
+
   /* Const/copy propagate into USES, VUSES and the RHS of VDEFs.  */
   cprop_into_stmt (stmt, m_evrp_range_analyzer);