[PATCH] Fix incorrect byte swap detection (PR tree-optimization/60454)

[Thomas Preud'homme]

The bswap optimization has a bug where a code can be incorrectly detected as 
doing a byte swap, therefore leading to change of behavior for the program 
compiled. This is tracked as PR60454. The patch below fixes the issue.

Best regards,

Thomas Preud'homme

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 748805e..b6d7d93 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,8 @@
+2014-03-07  Thomas Preud'homme  <thomas.preudho...@arm.com>
+
+       PR tree-optimization/60454
+       * tree-ssa-math-opts.c (find_bswap_1): Fix bswap detection.
+
 2014-02-23  David Holsgrove <david.holsgr...@xilinx.com>
 
        * config/microblaze/microblaze.md: Correct ashrsi_reg / lshrsi_reg names
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index f3c0c85..d3e0385 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,9 @@
+2014-03-07  Thomas Preud'homme  <thomas.preudho...@arm.com>
+
+       PR tree-optimization/60454
+       * gcc.dg/optimize-bswapsi-2.c (fake_swap32): Testcase to track
+       regression of PR60454.
+
 2014-02-23  David Holsgrove <david.holsgr...@xilinx.com>
 
        * gcc/testsuite/gcc.target/microblaze/others/mem_reload.c: New test.
diff --git a/gcc/testsuite/gcc.dg/optimize-bswapsi-2.c 
b/gcc/testsuite/gcc.dg/optimize-bswapsi-2.c
new file mode 100644
index 0000000..f20269e
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/optimize-bswapsi-2.c
@@ -0,0 +1,26 @@
+/* { dg-do compile { target arm*-*-* alpha*-*-* i?86-*-* powerpc*-*-* 
rs6000-*-* x86_64-*-* s390*-*-* } } */
+/* { dg-require-effective-target stdint_types } */
+/* { dg-options "-O2 -fdump-tree-bswap" } */
+/* { dg-options "-O2 -fdump-tree-bswap -march=z900" { target s390-*-* } } */
+
+#include <stdint.h>
+
+#define __fake_const_swab32(x) ((uint32_t)(                          \
+        (((uint32_t)(x) & (uint32_t)0x000000ffUL) << 24) |            \
+        (((uint32_t)(x) & (uint32_t)0x0000ff00UL) <<  8) |            \
+        (((uint32_t)(x) & (uint32_t)0x000000ffUL) <<  8) |            \
+        (((uint32_t)(x) & (uint32_t)0x0000ff00UL)      ) |            \
+        (((uint32_t)(x) & (uint32_t)0xff000000UL) >> 24)))
+
+/* Previous version of bswap optimization would detect byte swap when none
+   happen. This test aims at catching such wrong detection to avoid
+   regressions.  */
+
+uint32_t
+fake_swap32 (uint32_t in)
+{
+  return __fake_const_swab32 (in);
+}
+
+/* { dg-final { scan-tree-dump-times "32 bit bswap implementation found at" 0 
"bswap" } } */
+/* { dg-final { cleanup-tree-dump "bswap" } } */
diff --git a/gcc/tree-ssa-math-opts.c b/gcc/tree-ssa-math-opts.c
index 8e372ed..10a11ec 100644
--- a/gcc/tree-ssa-math-opts.c
+++ b/gcc/tree-ssa-math-opts.c
@@ -1801,7 +1801,9 @@ find_bswap_1 (gimple stmt, struct symbolic_number *n, int 
limit)
 
   if (rhs_class == GIMPLE_BINARY_RHS)
     {
+      int i;
       struct symbolic_number n1, n2;
+      unsigned HOST_WIDEST_INT mask;
       tree source_expr2;
 
       if (code != BIT_IOR_EXPR)
@@ -1827,6 +1829,15 @@ find_bswap_1 (gimple stmt, struct symbolic_number *n, 
int limit)
            return NULL_TREE;
 
          n->size = n1.size;
+         for (i = 0, mask = 0xff; i < n->size; i++, mask <<= 8)
+           {
+             unsigned HOST_WIDEST_INT masked1, masked2;
+
+             masked1 = n1.n & mask;
+             masked2 = n2.n & mask;
+             if (masked1 && masked2 && masked1 != masked2)
+               return NULL_TREE;
+           }
          n->n = n1.n | n2.n;
 
          if (!verify_symbolic_number_p (n, stmt))