LRA, rs6000, Darwin: Amend lo_sum use for forced constants [PR104117].

Two issues resulted in this PR, which manifests when we force a constant into
memory in LRA (in PIC code on Darwin).  The presence of such forced constants
is quite dependent on other RTL optimisations, and it is easy for the issue to
become latent for a specific case.

First, in the Darwin-specific rs6000 backend code, we were not being careful
enough in rejecting invalid symbolic addresses.  Specifically, when generating
PIC code, we require a SYMBOL_REF to be wrapped in an UNSPEC_MACHOPIC_OFFSET.

Second, LRA was attempting to load a register using an invalid lo_sum address.

Signed-off-by: Iain Sandoe <[email protected]>
Co-authored-by: Vladimir Makarov <[email protected]>

	PR target/104117

gcc/ChangeLog:

	* config/rs6000/rs6000.cc (darwin_rs6000_legitimate_lo_sum_const_p):
	Check for UNSPEC_MACHOPIC_OFFSET wrappers on symbolic addresses when
	emitting PIC code.
	(legitimate_lo_sum_address_p): Likewise.
	* lra-constraints.cc (process_address_1): Do not attempt to emit a reg
	load from an invalid lo_sum address.

gcc/config/rs6000/rs6000.cc

@@ -8317,8 +8317,14 @@ darwin_rs6000_legitimate_lo_sum_const_p (rtx x, machine_mode mode)
   if (GET_CODE (x) == CONST)
     x = XEXP (x, 0);
 
+  /* If we are building PIC code, then any symbol must be wrapped in an
+     UNSPEC_MACHOPIC_OFFSET so that it will get the picbase subtracted.  */
+  bool machopic_offs_p = false;
   if (GET_CODE (x) == UNSPEC && XINT (x, 1) == UNSPEC_MACHOPIC_OFFSET)
-    x =  XVECEXP (x, 0, 0);
+    {
+      x =  XVECEXP (x, 0, 0);
+      machopic_offs_p = true;
+    }
 
   rtx sym = NULL_RTX;
   unsigned HOST_WIDE_INT offset = 0;
@@ -8349,6 +8355,9 @@ darwin_rs6000_legitimate_lo_sum_const_p (rtx x, machine_mode mode)
   if (sym)
     {
       tree decl = SYMBOL_REF_DECL (sym);
+      /* As noted above, PIC code cannot use a bare SYMBOL_REF.  */
+      if (TARGET_MACHO && flag_pic && !machopic_offs_p)
+	return false;
 #if TARGET_MACHO
       if (MACHO_SYMBOL_INDIRECTION_P (sym))
       /* The decl in an indirection symbol is the original one, which might
@@ -8936,7 +8945,7 @@ legitimate_lo_sum_address_p (machine_mode mode, rtx x, int strict)
     return false;
   x = XEXP (x, 1);
 
-  if (TARGET_ELF || TARGET_MACHO)
+  if (TARGET_ELF)
     {
       bool large_toc_ok;
 
@@ -8962,7 +8971,32 @@ legitimate_lo_sum_address_p (machine_mode mode, rtx x, int strict)
 
       return CONSTANT_P (x) || large_toc_ok;
     }
+  else if (TARGET_MACHO)
+    {
+      if (GET_MODE_NUNITS (mode) != 1)
+	return false;
+      if (GET_MODE_SIZE (mode) > UNITS_PER_WORD
+	  && !(/* see above  */
+	       TARGET_HARD_FLOAT && (mode == DFmode || mode == DDmode)))
+	return false;
+#if TARGET_MACHO
+      if (MACHO_DYNAMIC_NO_PIC_P || !flag_pic)
+	return CONSTANT_P (x);
+#endif
+      /* Macho-O PIC code from here.  */
+      if (GET_CODE (x) == CONST)
+	x = XEXP (x, 0);
+
+      /* SYMBOL_REFs need to be wrapped in an UNSPEC_MACHOPIC_OFFSET.  */
+      if (SYMBOL_REF_P (x))
+	return false;
 
+      /* So this is OK if the wrapped object is const.  */
+      if (GET_CODE (x) == UNSPEC
+	  && XINT (x, 1) == UNSPEC_MACHOPIC_OFFSET)
+	return CONSTANT_P (XVECEXP (x, 0, 0));
+      return CONSTANT_P (x);
+    }
   return false;
 }
 

gcc/lra-constraints.cc

@@ -3625,21 +3625,8 @@ process_address_1 (int nop, bool check_only_p,
 		  *ad.inner = gen_rtx_LO_SUM (Pmode, new_reg, addr);
 		  if (!valid_address_p (op, &ad, cn))
 		    {
-		      /* Try to put lo_sum into register.  */
-		      insn = emit_insn (gen_rtx_SET
-					(new_reg,
-					 gen_rtx_LO_SUM (Pmode, new_reg, addr)));
-		      code = recog_memoized (insn);
-		      if (code >= 0)
-			{
-			  *ad.inner = new_reg;
-			  if (!valid_address_p (op, &ad, cn))
-			    {
-			      *ad.inner = addr;
-			      code = -1;
-			    }
-			}
-
+		      *ad.inner = addr; /* Punt.  */
+		      code = -1;
 		    }
 		}
 	      if (code < 0)