[PATCH] regrename: Fix -fcompare-debug issue in check_new_reg_p [PR105041]

[Surya Kumari Jangala via Gcc-patches]

regrename: Fix -fcompare-debug issue in check_new_reg_p [PR105041]

In check_new_reg_p, the nregs of a du chain is computed by obtaining the MODE
of the first element in the chain, and then calling hard_regno_nregs() with the
MODE. But the first element of the chain can be a DEBUG_INSN whose mode need
not be the same as the rest of the elements in the du chain. This
was resulting in fcompare-debug failure as check_new_reg_p was returning a
different result with -g for the same candidate register. We can instead obtain
nregs from the du chain itself.

2022-06-10  Surya Kumari Jangala  <jskum...@linux.ibm.com>

gcc/
        PR rtl-optimization/105041
        * regrename.cc (check_new_reg_p): Use nregs value from du chain.

gcc/testsuite/
        PR rtl-optimization/105041
        * gcc.target/powerpc/pr105041.c: New test.


diff --git a/gcc/regrename.cc b/gcc/regrename.cc
index 10271e1..f651351 100644
--- a/gcc/regrename.cc
+++ b/gcc/regrename.cc
@@ -324,8 +324,7 @@ static bool
 check_new_reg_p (int reg ATTRIBUTE_UNUSED, int new_reg,
                 class du_head *this_head, HARD_REG_SET this_unavailable)
 {
-  machine_mode mode = GET_MODE (*this_head->first->loc);
-  int nregs = hard_regno_nregs (new_reg, mode);
+  int nregs = this_head->nregs;
   int i;
   struct du_chain *tmp;
 
diff --git a/gcc/testsuite/gcc.target/powerpc/pr105041.c 
b/gcc/testsuite/gcc.target/powerpc/pr105041.c
new file mode 100644
index 0000000..89eed1c
--- /dev/null
+++ b/gcc/testsuite/gcc.target/powerpc/pr105041.c
@@ -0,0 +1,24 @@
+/* { dg-do compile } */
+/* { dg-require-effective-target be } */
+/* { dg-options "-m32 -mdejagnu-cpu=power4 -O2 -fcompare-debug 
-fharden-compares -frename-registers" } */
+
+double m;
+int n;
+
+unsigned int
+foo (unsigned int x, int y)
+{
+  long long int a = y, b = !a;
+  int c = 0;
+
+  if (b != x)
+    while ((int) m == a)
+      {
+        c = a;
+        a = 0;
+      }
+
+  n = b = y;
+
+  return x + c;
+}