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[PATCH][PR target/63347][P3 Regression] Fix SCHED_GROUP_P handling in haifa-sched.c



PR 63347 is a case where we can end up scheduling an insn into the middle of a scheduling group.

Basically given two consecutive insns A & B, if B has SCHED_GROUP_P set, then it must always be immediately after A.

The problem we ran into in this PR was that there was a cost to issue B, so it got delayed several cycles. While B was delayed an earlier, unrelated insn Z which had been delayed earlier became ready and issued. The result being A Z B which ultimately led to incorrect code generation.

The fix is actually quite simple. In prune_ready_list, we queue insns that have had their dependencies satisfied, but have a cost (say for example, they're waiting for a functional unit to become available). We want to queue based on that cost, with one exception. If the insn to be queued is part of a scheduling group, then we want to queue it with cost 1.

That ensures that on each cycle, any SCHED_GROUP_P insn that has its dependencies satisfied is in the ready list. Once we do that, everything is in place to assure that nothing issues until after the SCHED_GROUP_P insn issues.

Bootstrapped and regression tested on x86_64-unknown-linux-gnu. Also verified the testcase works correctly on m68k-unknown-linux. Installed on the trunk.





commit 07e421b3fbc2d29c9636200906c3edf3cbd33499
Author: Jeff Law <law@redhat.com>
Date:   Wed Feb 11 16:19:05 2015 -0700

    	PR target/63347
    	* haifa-sched.c (prune_ready_list): If we have a SCHED_GROUP_P insn
    	that needs to be queued, just queue it for a single cycle.
    
    	PR target/63347
    	* gcc.target/m68k/pr63347.c: New test.

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index d895209..c9ac045 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,9 @@
+2015-02-11  Jeff Law  <law@redhat.com>
+
+	PR target/63347
+	* haifa-sched.c (prune_ready_list): If we have a SCHED_GROUP_P insn
+	that needs to be queued, just queue it for a single cycle.
+
 2015-02-11  Jan Hubicka  <hubicka@ucw.cz>
 
 	* ipa.c (symbol_table::remove_unreachable_nodes): Avoid releasing
diff --git a/gcc/haifa-sched.c b/gcc/haifa-sched.c
index 75d2421..64c8c9c1 100644
--- a/gcc/haifa-sched.c
+++ b/gcc/haifa-sched.c
@@ -6291,7 +6291,15 @@ prune_ready_list (state_t temp_state, bool first_cycle_insn_p,
 	      if (SCHED_GROUP_P (insn) && cost > min_cost_group)
 		min_cost_group = cost;
 	      ready_remove (&ready, i);
-	      queue_insn (insn, cost, reason);
+	      /* Normally we'd want to queue INSN for COST cycles.  However,
+		 if SCHED_GROUP_P is set, then we must ensure that nothing
+		 else comes between INSN and its predecessor.  If there is
+		 some other insn ready to fire on the next cycle, then that
+		 invariant would be broken.
+
+		 So when SCHED_GROUP_P is set, just queue this insn for a
+		 single cycle.  */
+	      queue_insn (insn, SCHED_GROUP_P (insn) ? 1 : cost, reason);
 	      if (i + 1 < n)
 		break;
 	    }
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index c62cc23..ee5be51 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,8 @@
+2015-02-11  Jeff Law  <law@redhat.com>
+
+	PR target/63347
+	* gcc.target/m68k/pr63347.c: New test.
+
 2015-02-11  Marek Polacek  <polacek@redhat.com>
 
 	* g++.dg/ubsan/shift-1.C: New test.
diff --git a/gcc/testsuite/gcc.target/m68k/pr63347.c b/gcc/testsuite/gcc.target/m68k/pr63347.c
new file mode 100644
index 0000000..1d23e9a
--- /dev/null
+++ b/gcc/testsuite/gcc.target/m68k/pr63347.c
@@ -0,0 +1,46 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -mcpu=5208" } */
+
+#include <stdlib.h>
+
+void __attribute__ ((noinline))
+oof()
+{
+  asm volatile ("" ::: "memory");
+}
+int print_info(unsigned int *ip_addr)
+{
+    int invalid = 0;
+
+    if (ip_addr) {
+        unsigned int haddr = *ip_addr;
+        oof("stuff");
+        if (0x0 == haddr) {
+            invalid = 1;
+        }
+        oof("stuff2");
+    } else {
+        invalid = 1;
+    }
+
+    return invalid;
+}
+
+int main(int argc, char *argv[])
+{
+    unsigned int myaddr;
+    int ret;
+
+    myaddr = 0x0;
+    ret = print_info(&myaddr);
+    if (!ret)
+        abort ();
+
+    myaddr = 0x01020304;
+    ret = print_info(&myaddr);
+    if (ret)
+        abort ();
+    exit (0);
+}
+
+

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