Fix modref wrt __builtin_assume_aligned

__builtin_assume_aligned has bit contraictionary fnspec description "1cX "
which means that parameter 1 is returned but also unused.  PTA code takes
precedence to parameter being returned, while modref takes the info that
parameter is unused.  This patch tweaks modref to follow PTA semantics (as
suggested by Richard in the PR log)

gcc/ChangeLog:

2021-11-18  Jan Hubicka  <hubicka@ucw.cz>

	PR ipa/103266
	* ipa-modref.c (modref_eaf_analysis::merge_call_lhs_flags): Unused
	parameter may still be returned.
	(modref_eaf_analysis::analyze_ssa_name): Call merge_call_lhs_flags
	even for unused function args.

gcc/testsuite/ChangeLog:

2021-11-18  Jan Hubicka  <hubicka@ucw.cz>

	PR ipa/103266
	* g++.dg/torture/pr103266.C: New test.

2 files changed, 45 insertions, 10 deletions

diff --git a/gcc/ipa-modref.c b/gcc/ipa-modref.c
index c94f058..e5d2b11 100644
--- a/gcc/ipa-modref.c
+++ b/gcc/ipa-modref.c
@@ -2033,10 +2033,7 @@ modref_eaf_analysis::merge_call_lhs_flags (gcall *call, int arg,
 					   bool indirect)
 {
   int index = SSA_NAME_VERSION (name);
-
-  /* If value is not returned at all, do nothing.  */
-  if (!direct && !indirect)
-    return;
+  bool returned_directly = false;
 
   /* If there is no return value, no flags are affected.  */
   if (!gimple_call_lhs (call))
@@ -2047,10 +2044,23 @@ modref_eaf_analysis::merge_call_lhs_flags (gcall *call, int arg,
   if (arg >= 0)
     {
       int flags = gimple_call_return_flags (call);
-      if ((flags & ERF_RETURNS_ARG)
-	  && (flags & ERF_RETURN_ARG_MASK) != arg)
-	return;
+      if (flags & ERF_RETURNS_ARG)
+	{
+	  if ((flags & ERF_RETURN_ARG_MASK) == arg)
+	    returned_directly = true;
+	  else
+	   return;
+	}
+    }
+  /* Make ERF_RETURNS_ARG overwrite EAF_UNUSED.  */
+  if (returned_directly)
+    {
+      direct = true;
+      indirect = false;
     }
+  /* If value is not returned at all, do nothing.  */
+  else if (!direct && !indirect)
+    return;
 
   /* If return value is SSA name determine its flags.  */
   if (TREE_CODE (gimple_call_lhs (call)) == SSA_NAME)
@@ -2273,11 +2283,13 @@ modref_eaf_analysis::analyze_ssa_name (tree name)
 		if (gimple_call_arg (call, i) == name)
 		  {
 		    int call_flags = gimple_call_arg_flags (call, i);
-		    if (!ignore_retval && !(call_flags & EAF_UNUSED))
+		    if (!ignore_retval)
 		      merge_call_lhs_flags
 			      (call, i, name,
-			       !(call_flags & EAF_NOT_RETURNED_DIRECTLY),
-			       !(call_flags & EAF_NOT_RETURNED_INDIRECTLY));
+			       !(call_flags & (EAF_NOT_RETURNED_DIRECTLY
+					       | EAF_UNUSED)),
+			       !(call_flags & (EAF_NOT_RETURNED_INDIRECTLY
+					       | EAF_UNUSED)));
 		    if (!(ecf_flags & (ECF_CONST | ECF_NOVOPS)))
 		      {
 			call_flags = callee_to_caller_flags
diff --git a/gcc/testsuite/g++.dg/torture/pr103266.C b/gcc/testsuite/g++.dg/torture/pr103266.C
new file mode 100644
index 0000000..d5c13f5
--- /dev/null
+++ b/gcc/testsuite/g++.dg/torture/pr103266.C
@@ -0,0 +1,23 @@
+// { dg-do run }
+/* { dg-additional-options "-std=c++14" } */
+    typedef unsigned int u32;
+    typedef unsigned char u8;
+
+    static u32 pu8to32(const u8 * p8) __attribute__((noinline));
+    static u32 pu8to32(const u8 * p8) {
+      u32 v;
+    
+      __builtin_memcpy(&v, __builtin_assume_aligned(p8, 1), sizeof(u32));
+    
+      return v;
+    }
+    
+    int main(void) {
+      // dse1 throws this store away
+      u8 d[sizeof(u32)] = {
+          0x07, 0x00, 0x00, 0x07,
+      };
+    
+      if (pu8to32(d) != 0x07000007)
+        __builtin_trap();
+    }