lra: Tighten check for reloading paradoxical subregs [PR94052]

simplify_operand_subreg tries to detect whether the allocation for
a pseudo in a paradoxical subreg is also valid for the outer mode.
The condition it used to check for an invalid combination was:

  else if (REG_P (reg)
	   && REGNO (reg) >= FIRST_PSEUDO_REGISTER
	   && (hard_regno = lra_get_regno_hard_regno (REGNO (reg))) >= 0
	   && (hard_regno_nregs (hard_regno, innermode)
	       < hard_regno_nregs (hard_regno, mode))
	   && (regclass = lra_get_allocno_class (REGNO (reg)))
	   && (type != OP_IN
	       || !in_hard_reg_set_p (reg_class_contents[regclass],
				      mode, hard_regno)
	       || overlaps_hard_reg_set_p (lra_no_alloc_regs,
					   mode, hard_regno)))

I think there are two problems with this:

(1) It never actually checks whether the hard register is valid for the
    outer mode (in the hard_regno_mode_ok sense).  If it isn't, any attempt
    to reload in the outer mode is likely to cycle, because the implied
    regno/mode combination will be just as invalid next time
    curr_insn_transform sees the subreg.

(2) The check is valid for little-endian only.  For big-endian we need
    to move hard_regno backwards.

Using simplify_subreg_regno should avoid both problems.

As the existing comment says, IRA should always take subreg references
into account when allocating hard registers, so this fix-up should only
really be needed for pseudos allocated by LRA itself.

gcc/
2020-03-21  Richard Sandiford  <richard.sandiford@arm.com>

	PR rtl-optimization/94052
	* lra-constraints.c (simplify_operand_subreg): Reload the inner
	register of a paradoxical subreg if simplify_subreg_regno fails
	to give a valid hard register for the outer mode.

gcc/testsuite/
2020-03-21  Tamar Christina  <tamar.christina@arm.com>

	PR target/94052
	* gcc.target/aarch64/pr94052.C: New test.

4 files changed, 200 insertions, 10 deletions

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index c5d3fb9..e55a8e7 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,10 @@
+2020-03-21  Richard Sandiford  <richard.sandiford@arm.com>
+
+	PR rtl-optimization/94052
+	* lra-constraints.c (simplify_operand_subreg): Reload the inner
+	register of a paradoxical subreg if simplify_subreg_regno fails
+	to give a valid hard register for the outer mode.
+
 2020-03-20  Martin Jambor  <mjambor@suse.cz>
 
 	PR tree-optimization/93435
diff --git a/gcc/lra-constraints.c b/gcc/lra-constraints.c
index f71e0c9..bf6d4a2 100644
--- a/gcc/lra-constraints.c
+++ b/gcc/lra-constraints.c
@@ -1489,7 +1489,7 @@ static bool process_address (int, bool, rtx_insn **, rtx_insn **);
 static bool
 simplify_operand_subreg (int nop, machine_mode reg_mode)
 {
-  int hard_regno;
+  int hard_regno, inner_hard_regno;
   rtx_insn *before, *after;
   machine_mode mode, innermode;
   rtx reg, new_reg;
@@ -1735,15 +1735,19 @@ simplify_operand_subreg (int nop, machine_mode reg_mode)
      for the new uses.  */
   else if (REG_P (reg)
 	   && REGNO (reg) >= FIRST_PSEUDO_REGISTER
-	   && (hard_regno = lra_get_regno_hard_regno (REGNO (reg))) >= 0
-	   && (hard_regno_nregs (hard_regno, innermode)
-	       < hard_regno_nregs (hard_regno, mode))
-	   && (regclass = lra_get_allocno_class (REGNO (reg)))
-	   && (type != OP_IN
-	       || !in_hard_reg_set_p (reg_class_contents[regclass],
-				      mode, hard_regno)
-	       || overlaps_hard_reg_set_p (lra_no_alloc_regs,
-					   mode, hard_regno)))
+	   && paradoxical_subreg_p (operand)
+	   && (inner_hard_regno = lra_get_regno_hard_regno (REGNO (reg))) >= 0
+	   && ((hard_regno
+		= simplify_subreg_regno (inner_hard_regno, innermode,
+					 SUBREG_BYTE (operand), mode)) < 0
+	       || ((hard_regno_nregs (inner_hard_regno, innermode)
+		    < hard_regno_nregs (hard_regno, mode))
+		   && (regclass = lra_get_allocno_class (REGNO (reg)))
+		   && (type != OP_IN
+		       || !in_hard_reg_set_p (reg_class_contents[regclass],
+					      mode, hard_regno)
+		       || overlaps_hard_reg_set_p (lra_no_alloc_regs,
+						   mode, hard_regno)))))
     {
       /* The class will be defined later in curr_insn_transform.  */
       enum reg_class rclass
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index ce99c98..bff5d821 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,8 @@
+2020-03-21  Tamar Christina  <tamar.christina@arm.com>
+
+	PR target/94052
+	* gcc.target/aarch64/pr94052.C: New test.
+
 2020-03-20  Martin Jambor  <mjambor@suse.cz>
 
 	PR tree-optimization/93435
diff --git a/gcc/testsuite/g++.target/aarch64/pr94052.C b/gcc/testsuite/g++.target/aarch64/pr94052.C
new file mode 100644
index 0000000..d36c9bd
--- /dev/null
+++ b/gcc/testsuite/g++.target/aarch64/pr94052.C
@@ -0,0 +1,174 @@
+/* { dg-do compile } */
+/* { dg-additional-options "-O2 -std=gnu++11 -w" } */
+
+namespace c {
+typedef int d;
+template <typename e> struct f { typedef e g; };
+template <bool, typename> struct h;
+template <typename e> e aa(typename f<e>::g i) { return i; }
+template <typename, typename> struct j {};
+template <d, typename> struct k;
+template <class l, class m> struct k<1, j<l, m>> { typedef m g; };
+template <d n, class l, class m> typename k<n, j<l, m>>::g ab(j<l, m>);
+} // namespace c
+typedef long d;
+typedef char o;
+typedef int p;
+typedef char q;
+typedef int r;
+namespace {
+struct s;
+constexpr d t = 6;
+template <typename> class ad {
+public:
+  static constexpr d u = t;
+  d v();
+  d x();
+  d y();
+};
+class z : ad<int> {};
+struct ae {
+  p af;
+};
+class ag {
+public:
+  ae ah();
+};
+} // namespace
+typedef __Int32x4_t ai;
+typedef struct {
+  ai aj[2];
+} ak;
+typedef int al;
+void am(p *a, ai b) { __builtin_aarch64_st1v4si(a, b); }
+namespace an {
+class ao {
+public:
+  bool operator==(ao);
+  d v();
+  d x();
+};
+class ap : public ad<r> {};
+class aq {
+public:
+  c::j<int, int> ar();
+  int as();
+  int at();
+};
+class au {
+public:
+  virtual d av(d);
+  virtual ap aw();
+  virtual ag ax();
+};
+class ay {};
+class az {
+  virtual void ba(const ay &, const s &);
+};
+using bb = az;
+class bc;
+class bd : bb {
+  void ba(const ay &, const s &);
+  bc *be;
+  bc *bf;
+  bc *bg;
+  aq bh;
+  int bi;
+  int bj;
+  ao bk;
+};
+namespace bl {
+namespace bm {
+namespace bn {
+class bo;
+}
+} // namespace bm
+} // namespace bl
+namespace bn {
+template <typename ac = c::h<0, bl::bm ::bn::bo>>
+ai bp(ac *, ac *, ac *, al, al, al, d, p);
+template <typename ac = c::h<0, bl::bm ::bn::bo>>
+ak bq(ac *br, ac *bs, ac *bt, al bu, al bv, al bw, d bx, int, int by) {
+  ak{bp(br, bs, bt, bu, bv, bw, bx, by), bp(br, bs, bt, bu, bv, bw, bx, by)};
+}
+template <typename ac = c::h<0, bl::bm ::bn::bo>>
+ak bz(ac *, ac *, ac *, al, al, al &, int, p);
+template <int> void ca(p *, const ak &);
+template <> void ca<1>(p *buffer, const ak &cb) {
+  am(buffer, cb.aj[0]);
+  am(buffer + 4, cb.aj[1]);
+}
+int cc(int, int);
+} // namespace bn
+class bc {
+public:
+  virtual au *cd();
+};
+class ce {
+public:
+  q *cf();
+};
+template <d> struct cg {
+  template <typename ch> static void ci(ay, z cj, ch ck) { ck(cj); }
+};
+template <typename ch> void cl(ay w, ch ck) {
+  z cj;
+  cg<z::u>::ci(w, cj, c::aa<ch>(ck));
+}
+namespace {
+template <typename T1, typename cm, int cn> class co {
+public:
+  static void convolve(ay, int cs, bc *cp, bc *cq, bc *cr, aq cw, int, ao ct) {
+    int by = cp->cd()->ax().ah().af;
+    int cu = cq->cd()->ax().ah().af;
+    cp->cd()->aw().v();
+    int cv = cp->cd()->aw().x();
+    cp->cd()->aw().y();
+    cp->cd()->aw();
+    int da = cr->cd()->aw().x();
+    int cx = cq->cd()->aw().x();
+    cq->cd()->aw().y();
+    int cy = cr->cd()->av(0);
+    int cz = cr->cd()->av(1);
+    bn::cc(cs, cn);
+    int de = c::ab<1>(cw.ar());
+    cw.as();
+    cw.at();
+    ay db;
+    ce dc;
+    ce dd;
+    ce w;
+    q *di = w.cf();
+    cl(db, [&](z) {
+      int df;
+      dc;
+      di;
+      cx;
+      auto dg(cu);
+      auto dh(cu);
+      auto dl(cu);
+      for (; cz; df += de) {
+        auto br = reinterpret_cast<T1 *>(cv);
+        auto bs = reinterpret_cast<T1 *>(cv);
+        auto bt = reinterpret_cast<T1 *>(df * ct.x());
+        auto dj = reinterpret_cast<cm *>(dd.cf() + da);
+        for (int dk; dk < cy; dk += cs, dj += cs)
+          if (ct == ao()) {
+            auto vres = bn::bz(br, bs, bt, dg, dh, dl, cn, by);
+            bn::ca<cn>(dj, vres);
+          } else
+            bn::bq(br, bs, bt, dg, dh, dl, ct.v(), cn, by);
+      }
+    });
+  }
+};
+template <typename T1, typename cm>
+void bz(ay dm, int cs, bc *cp, bc *cq, bc *cr, aq cw, int dn, ao ct) {
+  co<T1, cm, 1>::convolve(dm, cs, cp, cq, cr, cw, dn, ct);
+  co<T1, cm, 2>::convolve(dm, cs, cp, cq, cr, cw, dn, ct);
+}
+} // namespace
+void bd::ba(const ay &dm, const s &) {
+  bz<o, p>(dm, bi, be, bg, bf, bh, bj, bk);
+}
+} // namespace an