[PATCH] arm, mve: Fix arm_mve_dlstp_check_dec_counter's use of single_pred

[Andre Vieira (lists)]

Hi,

Looks like single_pred ICEs if the basic-block does not have a single 
predecessor rather than return NULL, which was what this snippet of code 
relied on.
This feels like borderline obvious to me as a fix, but I thought I'd get 
it checked by one more person.

Call 'single_pred_p' before 'single_pred' to verify it is safe to do so.

gcc/ChangeLog:

        * config/arm/arm.cc (arm_mve_dlstp_check_dec_counter): Call
        single_pred_p to verify it's safe to call single_pred.

gcc/testsuite/ChangeLog:

        * gcc.target/arm/mve/dlstp-loop-form.c: Add loop that triggered ICE.diff --git a/gcc/config/arm/arm.cc b/gcc/config/arm/arm.cc
index 
0f72f3a9031237192c6362760203fe489946b948..030af7c801f8afeb9577b4e7d7637c17d6f5f638
 100644
--- a/gcc/config/arm/arm.cc
+++ b/gcc/config/arm/arm.cc
@@ -35370,9 +35370,10 @@ arm_mve_dlstp_check_dec_counter (loop *loop, rtx_insn* 
vctp_insn,
     return NULL;
   else if (REG_P (condconst))
     {
-      basic_block pre_loop_bb = single_pred (loop_preheader_edge (loop)->src);
-      if (!pre_loop_bb)
+      basic_block preheader_b = loop_preheader_edge (loop)->src;
+      if (!single_pred_p (preheader_b))
        return NULL;
+      basic_block pre_loop_bb = single_pred (preheader_b);
 
       rtx initial_compare = NULL_RTX;
       if (!(prev_nonnote_nondebug_insn_bb (BB_END (pre_loop_bb))
diff --git a/gcc/testsuite/gcc.target/arm/mve/dlstp-loop-form.c 
b/gcc/testsuite/gcc.target/arm/mve/dlstp-loop-form.c
index 
a1b26873d7908035c726e3724c91b186c697bc60..08811cef5687e94676db3d27be521602a60e7600
 100644
--- a/gcc/testsuite/gcc.target/arm/mve/dlstp-loop-form.c
+++ b/gcc/testsuite/gcc.target/arm/mve/dlstp-loop-form.c
@@ -25,3 +25,15 @@ void n() {
   }
 }
 
+int a;
+void g2() {
+  long b;
+  while (a) {
+    char *c;
+    for (long d = b; d > 0; d -= 4) {
+      mve_pred16_t e = vctp32q(d);
+      int32x4_t f;
+      vstrbq_p_s32(c, f, e);
+    }
+  }
+}