[gcc/devel/ranger] cfgexpand: Update partition size when merging variables

[Aldy Hernandez]

https://gcc.gnu.org/g:7c46e71d016c86971ac26c6fa38d76482859f296

commit 7c46e71d016c86971ac26c6fa38d76482859f296
Author: Richard Sandiford <richard.sandiford@arm.com>
Date:   Tue Jan 21 18:22:38 2020 +0000

    cfgexpand: Update partition size when merging variables
    
    cfgexpand sorts variables by decreasing size, so when merging a later
    variable into an earlier one, there's usually no need to update the
    merged size.
    
    But for poly_int sizes, the sort function just uses a lexicographical
    comparison of the coefficients, so e.g. 2X+2 comes before 0X+32.
    Which is bigger depends on the runtime value of X.
    
    This patch therefore takes the upper bound of the two sizes, which
    is conservatively correct for variable-length vectors and a no-op
    on other targets.
    
    It's probably a bad idea to merge fixed-length and variable-length
    variables in practice, but that's really an optimisation decision.
    I think we should have this patch as a correctness fix either way.
    
    This is easiest to test using the ACLE, but in principle it could happen
    for autovectorised code too, e.g. when using OpenMP vector variables.
    It's therefore a regression from GCC 8.
    
    2020-01-22  Richard Sandiford  <richard.sandiford@arm.com>
    
    gcc/
            * cfgexpand.c (union_stack_vars): Update the size.
    
    gcc/testsuite/
            * gcc.target/aarch64/sve/acle/general/stack_vars_1.c: New test.

Diff:
---
 gcc/ChangeLog                                      |  4 +++
 gcc/cfgexpand.c                                    |  3 ++
 gcc/testsuite/ChangeLog                            |  4 +++
 .../aarch64/sve/acle/general/stack_vars_1.c        | 32 ++++++++++++++++++++++
 4 files changed, 43 insertions(+)

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 2f229b92d7a..272968a3396 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,7 @@
+2020-01-22  Richard Sandiford  <richard.sandiford@arm.com>
+
+	* cfgexpand.c (union_stack_vars): Update the size.
+
 2020-01-22  Richard Biener  <rguenther@suse.de>
 
 	PR tree-optimization/93381
diff --git a/gcc/cfgexpand.c b/gcc/cfgexpand.c
index fb0575b146e..9864e4344d2 100644
--- a/gcc/cfgexpand.c
+++ b/gcc/cfgexpand.c
@@ -862,6 +862,9 @@ union_stack_vars (size_t a, size_t b)
   stack_vars[b].representative = a;
   stack_vars[a].next = b;
 
+  /* Make sure A is big enough to hold B.  */
+  stack_vars[a].size = upper_bound (stack_vars[a].size, stack_vars[b].size);
+
   /* Update the required alignment of partition A to account for B.  */
   if (stack_vars[a].alignb < stack_vars[b].alignb)
     stack_vars[a].alignb = stack_vars[b].alignb;
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index 3bd6407aac2..d22747b1dfe 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,7 @@
+2020-01-22  Richard Sandiford  <richard.sandiford@arm.com>
+
+	* gcc.target/aarch64/sve/acle/general/stack_vars_1.c: New test.
+
 2020-01-22  Richard Sandiford  <richard.sandiford@arm.com>
 
 	* gcc.target/aarch64/sve/tls_preserve_1.c: Require tls_native.
diff --git a/gcc/testsuite/gcc.target/aarch64/sve/acle/general/stack_vars_1.c b/gcc/testsuite/gcc.target/aarch64/sve/acle/general/stack_vars_1.c
new file mode 100644
index 00000000000..860fa67fbe6
--- /dev/null
+++ b/gcc/testsuite/gcc.target/aarch64/sve/acle/general/stack_vars_1.c
@@ -0,0 +1,32 @@
+/* { dg-do run { target aarch64_sve_hw } } */
+/* { dg-additional-options "-O2" } */
+
+#include <arm_sve.h>
+
+struct s { int x[32]; };
+
+void __attribute__((noipa)) consume (void *ptr) {}
+
+void __attribute__((noipa))
+check_var (svint32_t *ptr)
+{
+  svbool_t pg = svptrue_b8 ();
+  if (svptest_any (pg, svcmpne (pg, *ptr, svindex_s32 (0, 1))))
+    __builtin_abort ();
+}
+
+int
+main (void)
+{
+  svint32_t res = svindex_s32 (0, 1);
+  {
+    __SVBool_t pg = svptrue_b8 ();
+    consume (&pg);
+  }
+  {
+    struct s zeros = { 0 };
+    consume (&zeros);
+  }
+  check_var (&res);
+  return 0;
+}