ifcvt: Check for asm goto at the end of then_bb/else_bb in ifcvt [PR103908]

On the following testcase, RTL ifcvt sees then_bb
(note 7 6 8 3 [bb 3] NOTE_INSN_BASIC_BLOCK)
(insn 8 7 9 3 (set (mem/c:SI (symbol_ref:DI ("b") [flags 0x2]  <var_decl 0x7fdccf5b0cf0 b>) [1 b+0 S4 A32])
        (const_int 1 [0x1])) "pr103908.c":6:7 81 {*movsi_internal}
     (nil))
(jump_insn 9 8 13 3 (parallel [
            (asm_operands/v ("# insn 1") ("") 0 []
                 []
                 [
                    (label_ref:DI 21)
                ] pr103908.c:7)
            (clobber (reg:CC 17 flags))
        ]) "pr103908.c":7:5 -1
     (expr_list:REG_UNUSED (reg:CC 17 flags)
        (nil))
 -> 21)
and similarly else_bb (just with a different asm_operands template).
It checks that those basic blocks have a single successor and
uses last_active_insn which intentionally skips over JUMP_INSNs, sees
both basic blocks contain the same set and merges them (or if the
sets are different, attempts some other noce optimization).
But we can't assume that the jump, even when it has only a single successor,
has no side-effects.

The following patch fixes it by punting if test_bb ends with a JUMP_INSN
that isn't onlyjump_p.

2022-01-06  Jakub Jelinek  <jakub@redhat.com>

	PR rtl-optimization/103908
	* ifcvt.c (bb_valid_for_noce_process_p): Punt on bbs ending with
	asm goto.

	* gcc.target/i386/pr103908.c: New test.

(cherry picked from commit 80ad67e2af0620d58d57d0406dc22693cf5b8ca9)

diff --git a/gcc/ifcvt.c b/gcc/ifcvt.c
index 977dd1bd403a03a234758b564f07f1bdf4d4763a..4baf07a7e97add52b68c8d63ff4da91ae3f0a54c 100644 (file)
--- a/gcc/ifcvt.c
+++ b/gcc/ifcvt.c
@@ -3064,6 +3064,12 @@ bb_valid_for_noce_process_p (basic_block test_bb, rtx cond,
 
   if (!insn_valid_noce_process_p (last_insn, cc))
     return false;
+
+  /* Punt on blocks ending with asm goto or jumps with other side-effects,
+     last_active_insn ignores JUMP_INSNs.  */
+  if (JUMP_P (BB_END (test_bb)) && !onlyjump_p (BB_END (test_bb)))
+    return false;
+
   last_set = single_set (last_insn);
 
   rtx x = SET_DEST (last_set);

diff --git a/gcc/testsuite/gcc.target/i386/pr103908.c b/gcc/testsuite/gcc.target/i386/pr103908.c
new file mode 100644 (file)
index 0000000..7c57e1d
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/pr103908.c
@@ -0,0 +1,24 @@
+/* PR rtl-optimization/103908 */
+/* { dg-do compile } */
+/* { dg-options "-O1 -fdisable-tree-cselim -fno-tree-sink" } */
+/* { dg-final { scan-assembler "# insn 1" } } */
+/* { dg-final { scan-assembler "# insn 2" } } */
+
+int a, b;
+
+void
+foo (void)
+{
+  if (a)
+    {
+      b = 1;
+      asm goto ("# insn 1" : : : : lab1);
+    lab1:;
+    }
+  else
+    {
+      b = 1;
+      asm goto ("# insn 2" : : : : lab2);
+    lab2:;
+    }
+}