[gcc r15-1619] ira: Scale save/restore costs of callee save registers with block frequency

[Surya Kumari Jangala]

https://gcc.gnu.org/g:3b9b8d6cfdf59337f4b7ce10ce92a98044b2657b

commit r15-1619-g3b9b8d6cfdf59337f4b7ce10ce92a98044b2657b
Author: Surya Kumari Jangala <jskumari@linux.ibm.com>
Date:   Tue Jun 25 08:37:49 2024 -0500

    ira: Scale save/restore costs of callee save registers with block frequency
    
    In assign_hard_reg(), when computing the costs of the hard registers, the
    cost of saving/restoring a callee-save hard register in prolog/epilog is
    taken into consideration. However, this cost is not scaled with the entry
    block frequency. Without scaling, the cost of saving/restoring is quite
    small and this can result in a callee-save register being chosen by
    assign_hard_reg() even though there are free caller-save registers
    available. Assigning a callee save register to a pseudo that is live
    in the entire function and across a call will cause shrink wrap to fail.
    
    2024-06-25  Surya Kumari Jangala  <jskumari@linux.ibm.com>
    
    gcc/
            PR rtl-optimization/111673
            * ira-color.cc (assign_hard_reg): Scale save/restore costs of
            callee save registers with block frequency.
    
    gcc/testsuite/
            PR rtl-optimization/111673
            * gcc.target/powerpc/pr111673.c: New test.

Diff:
---
 gcc/ira-color.cc                            |  4 +++-
 gcc/testsuite/gcc.target/powerpc/pr111673.c | 17 +++++++++++++++++
 2 files changed, 20 insertions(+), 1 deletion(-)

diff --git a/gcc/ira-color.cc b/gcc/ira-color.cc
index b9ae32d1b4d..ca32a23a0c9 100644
--- a/gcc/ira-color.cc
+++ b/gcc/ira-color.cc
@@ -2178,7 +2178,9 @@ assign_hard_reg (ira_allocno_t a, bool retry_p)
 	    add_cost = ((ira_memory_move_cost[mode][rclass][0]
 		         + ira_memory_move_cost[mode][rclass][1])
 		        * saved_nregs / hard_regno_nregs (hard_regno,
-							  mode) - 1);
+							  mode) - 1)
+		       * (optimize_size ? 1 :
+			  REG_FREQ_FROM_BB (ENTRY_BLOCK_PTR_FOR_FN (cfun)));
 	    cost += add_cost;
 	    full_cost += add_cost;
 	  }
diff --git a/gcc/testsuite/gcc.target/powerpc/pr111673.c b/gcc/testsuite/gcc.target/powerpc/pr111673.c
new file mode 100644
index 00000000000..e0c0f85460a
--- /dev/null
+++ b/gcc/testsuite/gcc.target/powerpc/pr111673.c
@@ -0,0 +1,17 @@
+/* { dg-do compile { target lp64 } } */
+/* { dg-options "-O2 -fdump-rtl-pro_and_epilogue" } */
+
+/* Verify there is an early return without the prolog and shrink-wrap
+   the function. */
+
+int f (int);
+int
+advance (int dz)
+{
+  if (dz > 0)
+    return (dz + dz) * dz;
+  else
+    return dz * f (dz);
+}
+
+/* { dg-final { scan-rtl-dump-times "Performing shrink-wrapping" 1 "pro_and_epilogue" } } */