[gcc r11-10169] tree-optimization/105618 - restore load sinking

[gcc r11-10169] tree-optimization/105618 - restore load sinking

[Richard Biener]

https://gcc.gnu.org/g:dba0883cbbd0ce7545041be96ae75db1d577affb

commit r11-10169-gdba0883cbbd0ce7545041be96ae75db1d577affb
Author: Richard Biener <rguenther@suse.de>
Date:   Tue May 17 09:45:02 2022 +0200

    tree-optimization/105618 - restore load sinking
    
    The PR97330 fix caused some missed sinking of loads out of loops
    the following patch re-instantiates.
    
    2022-05-17  Richard Biener  <rguenther@suse.de>
    
            PR tree-optimization/105618
            * tree-ssa-sink.c (statement_sink_location): For virtual
            PHI uses ignore those defining the used virtual operand.
    
            * gcc.dg/tree-ssa/ssa-sink-19.c: New testcase.
    
    (cherry picked from commit ebce0e9bd8d714a8607ae24331a3d842b0d11859)

Diff:
---
 gcc/testsuite/gcc.dg/tree-ssa/ssa-sink-19.c | 21 +++++++++++++++++++++
 gcc/tree-ssa-sink.c                         |  3 +++
 2 files changed, 24 insertions(+)

diff --git a/gcc/testsuite/gcc.dg/tree-ssa/ssa-sink-19.c b/gcc/testsuite/gcc.dg/tree-ssa/ssa-sink-19.c
new file mode 100644
index 00000000000..f3eb0ef3a4e
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/ssa-sink-19.c
@@ -0,0 +1,21 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-sink-details -fdump-tree-cddce2-details" } */
+
+static int b=4;
+int c;
+
+int
+main()
+{
+  int e[5] = {1,1,1,1,1};
+  for (; b >= 0; b--) {
+    c = e[b];
+  }
+  return 0;
+}
+
+/* We should sink e[b] out of the loop which is possible after
+   applying store motion to c and b.  */
+/* { dg-final { scan-tree-dump "Sinking # VUSE" "sink" } } */
+/* And remove the loop after final value replacement.  */
+/* { dg-final { scan-tree-dump "fix_loop_structure: removing loop" "cddce2" } } */
diff --git a/gcc/tree-ssa-sink.c b/gcc/tree-ssa-sink.c
index 3c2ed795f85..b3097531203 100644
--- a/gcc/tree-ssa-sink.c
+++ b/gcc/tree-ssa-sink.c
@@ -390,6 +390,9 @@ statement_sink_location (gimple *stmt, basic_block frombb,
 		 with the use.  */
 	      if (gimple_code (use_stmt) == GIMPLE_PHI)
 		{
+		  /* If the PHI defines the virtual operand, ignore it.  */
+		  if (gimple_phi_result (use_stmt) == gimple_vuse (stmt))
+		    continue;
 		  /* In case the PHI node post-dominates the current insert
 		     location we can disregard it.  But make sure it is not
 		     dominating it as well as can happen in a CFG cycle.  */