[ira] avoid resetting ira_reg_equiv for function invariants

An aarch64 toolchain built with --enable-default-pie fails
gcc.target/aarch64/sme/nonlocal_goto_[123].c because the register
allocator ends up resetting equivalences, so it concludes it needs to
preserve a rematerializable function invariant across a call instead
of rematerializing it.

Restore the find_reg_equiv_invariant_const logic that was in place
before commit 55a2c3226a3e90a6d65f19710bab1ac377054234 rewrote it and
added a (spurious?) requirement for non-function-invariants to retain
an equivalence when other PIC-related conditions didn't apply.  That
requirement seems either reversed or unnecessary.

for  gcc/ChangeLog

	* ira.cc (setup_reg_equiv): Retain function invariant
	equivalences.

diff --git a/gcc/ira.cc b/gcc/ira.cc
index 4eebc9c4c50fb0338d714890fed3c120c485e178..3e15966558edfca1f8c40124681faa6e4f18e4e9 100644 (file)
--- a/gcc/ira.cc
+++ b/gcc/ira.cc
@@ -4233,12 +4233,14 @@ setup_reg_equiv (void)
                            && REGNO (SET_SRC (set)) == (unsigned int) i);
                x = SET_DEST (set);
              }
-           if (! function_invariant_p (x)
+           /* If PIC is enabled and the equiv is not a LEGITIMATE_PIC_OPERAND,
+              we can't use it.  */
+           if (! CONSTANT_P (x)
                || ! flag_pic
                /* A function invariant is often CONSTANT_P but may
                   include a register.  We promise to only pass
                   CONSTANT_P objects to LEGITIMATE_PIC_OPERAND_P.  */
-               || (CONSTANT_P (x) && LEGITIMATE_PIC_OPERAND_P (x)))
+               || LEGITIMATE_PIC_OPERAND_P (x))
              {
                /* It can happen that a REG_EQUIV note contains a MEM
                   that is not a legitimate memory operand.  As later