[PATCH 4/19]middle-end: Fix scale_loop_frequencies segfault on multiple-exits

[Tamar Christina via Gcc-patches]

Hi All,

There's an existing bug in loop frequency scaling where the if statement checks
to see if there's a single exit, and records an dump file note but then
continues.

It then tries to access the null pointer, which of course fails.

For multiple loop exists it's not really clear how to scale the exit
probablities as it's really unknown which exit is most probably.

For that reason I ignore the exit edges during scaling but still adjust the
loop body.

Bootstrapped Regtested on aarch64-none-linux-gnu and no issues.

Ok for master?

Thanks,
Tamar

gcc/ChangeLog:

        * cfgloopmanip.cc (scale_loop_frequencies): Fix typo.
        (scale_loop_profile): Don't access null pointer.

--- inline copy of patch -- 
diff --git a/gcc/cfgloopmanip.cc b/gcc/cfgloopmanip.cc
index 
6e09dcbb0b1864bc64ffd570a4b923f50c3819b5..b10ef3d2be82902ccd74e52a4318217b2db13bcb
 100644
--- a/gcc/cfgloopmanip.cc
+++ b/gcc/cfgloopmanip.cc
@@ -501,7 +501,7 @@ scale_loop_frequencies (class loop *loop, 
profile_probability p)
 /* Scale profile in LOOP by P.
    If ITERATION_BOUND is non-zero, scale even further if loop is predicted
    to iterate too many times.
-   Before caling this function, preheader block profile should be already
+   Before calling this function, preheader block profile should be already
    scaled to final count.  This is necessary because loop iterations are
    determined by comparing header edge count to latch ege count and thus
    they need to be scaled synchronously.  */
@@ -597,14 +597,14 @@ scale_loop_profile (class loop *loop, profile_probability 
p,
       /* If latch exists, change its count, since we changed
         probability of exit.  Theoretically we should update everything from
         source of exit edge to latch, but for vectorizer this is enough.  */
-      if (loop->latch && loop->latch != e->src)
+      if (e && loop->latch && loop->latch != e->src)
        loop->latch->count += count_delta;
 
       /* Scale the probabilities.  */
       scale_loop_frequencies (loop, p);
 
       /* Change latch's count back.  */
-      if (loop->latch && loop->latch != e->src)
+      if (e && loop->latch && loop->latch != e->src)
        loop->latch->count -= count_delta;
 
       if (dump_file && (dump_flags & TDF_DETAILS))




-- 

diff --git a/gcc/cfgloopmanip.cc b/gcc/cfgloopmanip.cc
index 
6e09dcbb0b1864bc64ffd570a4b923f50c3819b5..b10ef3d2be82902ccd74e52a4318217b2db13bcb
 100644
--- a/gcc/cfgloopmanip.cc
+++ b/gcc/cfgloopmanip.cc
@@ -501,7 +501,7 @@ scale_loop_frequencies (class loop *loop, 
profile_probability p)
 /* Scale profile in LOOP by P.
    If ITERATION_BOUND is non-zero, scale even further if loop is predicted
    to iterate too many times.
-   Before caling this function, preheader block profile should be already
+   Before calling this function, preheader block profile should be already
    scaled to final count.  This is necessary because loop iterations are
    determined by comparing header edge count to latch ege count and thus
    they need to be scaled synchronously.  */
@@ -597,14 +597,14 @@ scale_loop_profile (class loop *loop, profile_probability 
p,
       /* If latch exists, change its count, since we changed
         probability of exit.  Theoretically we should update everything from
         source of exit edge to latch, but for vectorizer this is enough.  */
-      if (loop->latch && loop->latch != e->src)
+      if (e && loop->latch && loop->latch != e->src)
        loop->latch->count += count_delta;
 
       /* Scale the probabilities.  */
       scale_loop_frequencies (loop, p);
 
       /* Change latch's count back.  */
-      if (loop->latch && loop->latch != e->src)
+      if (e && loop->latch && loop->latch != e->src)
        loop->latch->count -= count_delta;
 
       if (dump_file && (dump_flags & TDF_DETAILS))