[gcc r11-10156] regrename: Fix -fcompare-debug issue in check_new_reg_p [PR105041]

[Surya Kumari Jangala <jskumari@gcc.gnu.org>]

https://gcc.gnu.org/g:8522fab3f900d6fe0cc43be52fdd850f5c9c44db

commit r11-10156-g8522fab3f900d6fe0cc43be52fdd850f5c9c44db
Author: Surya Kumari Jangala <jskumari@linux.vnet.ibm.com>
Date:   Fri Jun 10 19:52:57 2022 +0530

    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  <jskumari@linux.ibm.com>
    
    gcc/
            PR rtl-optimization/105041
            * regrename.c (check_new_reg_p): Use nregs value from du chain.
    
    gcc/testsuite/
            PR rtl-optimization/105041
            * gcc.target/powerpc/pr105041.c: New test.
    
    (cherry picked from commit 3e16b4359e86b36676ed01219e6deafa95f3c16b)

Diff:
---
 gcc/regrename.c                             |  3 +--
 gcc/testsuite/gcc.target/powerpc/pr105041.c | 22 ++++++++++++++++++++++
 2 files changed, 23 insertions(+), 2 deletions(-)

diff --git a/gcc/regrename.c b/gcc/regrename.c
index c0d4643f802..0cf93d323d9 100644
--- a/gcc/regrename.c
+++ b/gcc/regrename.c
@@ -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 00000000000..c52b7a5ef30
--- /dev/null
+++ b/gcc/testsuite/gcc.target/powerpc/pr105041.c
@@ -0,0 +1,22 @@
+/* { dg-options "-mdejagnu-cpu=power4 -O2 -fcompare-debug -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;
+}