[gcc(refs/users/aoliva/heads/testme)] introduce asmnesia internal function

[Alexandre Oliva <aoliva@gcc.gnu.org>]

https://gcc.gnu.org/g:fb9654708bf23afa4300224c6e74bf771e06933d

commit fb9654708bf23afa4300224c6e74bf771e06933d
Author: Alexandre Oliva <oliva@adacore.com>
Date:   Sat Nov 20 06:10:25 2021 -0300

    introduce asmnesia internal function

Diff:
---
 gcc/gimple-harden-conditionals.cc | 17 ++-------------
 gcc/internal-fn.c                 | 44 +++++++++++++++++++++++++++++++++++++++
 gcc/internal-fn.def               |  4 ++++
 3 files changed, 50 insertions(+), 15 deletions(-)

diff --git a/gcc/gimple-harden-conditionals.cc b/gcc/gimple-harden-conditionals.cc
index cfa2361d65b..3768b2e23bd 100644
--- a/gcc/gimple-harden-conditionals.cc
+++ b/gcc/gimple-harden-conditionals.cc
@@ -132,21 +132,8 @@ detach_value (location_t loc, gimple_stmt_iterator *gsip, tree val)
   tree ret = make_ssa_name (TREE_TYPE (val));
   SET_SSA_NAME_VAR_OR_IDENTIFIER (ret, SSA_NAME_IDENTIFIER (val));
 
-  /* Output asm ("" : "=g" (ret) : "0" (val));  */
-  vec<tree, va_gc> *inputs = NULL;
-  vec<tree, va_gc> *outputs = NULL;
-  vec_safe_push (outputs,
-		 build_tree_list
-		 (build_tree_list
-		  (NULL_TREE, build_string (2, "=g")),
-		  ret));
-  vec_safe_push (inputs,
-		 build_tree_list
-		 (build_tree_list
-		  (NULL_TREE, build_string (1, "0")),
-		  val));
-  gasm *detach = gimple_build_asm_vec ("", inputs, outputs,
-				       NULL, NULL);
+  gcall *detach = gimple_build_call_internal (IFN_ASMNESIA, 1, val);
+  gimple_call_set_lhs (detach, ret);
   gimple_set_location (detach, loc);
   gsi_insert_before (gsip, detach, GSI_SAME_STMT);
 
diff --git a/gcc/internal-fn.c b/gcc/internal-fn.c
index e5b85f0db0e..ff1e4413369 100644
--- a/gcc/internal-fn.c
+++ b/gcc/internal-fn.c
@@ -3234,6 +3234,50 @@ expand_LAUNDER (internal_fn, gcall *call)
   expand_assignment (lhs, gimple_call_arg (call, 0), false);
 }
 
+/* Expand ASMNESIA to assignment and asm that makes the value unknown.  */
+
+static void
+expand_ASMNESIA (internal_fn, gcall *call)
+{
+  tree to = gimple_call_lhs (call);
+
+  if (!to)
+    return;
+
+  location_t locus = gimple_location (call);
+
+  tree from = gimple_call_arg (call, 0);
+
+  rtx to_rtx = expand_expr (to, NULL_RTX, VOIDmode, EXPAND_WRITE);
+
+  rtx from_rtx = expand_expr (from, NULL_RTX, VOIDmode, EXPAND_NORMAL);
+
+  enum machine_mode mode = GET_MODE (to_rtx);
+
+  gcc_checking_assert (mode != BLKmode && mode != VOIDmode
+		       && (GET_MODE (from_rtx) == mode
+			   || GET_MODE (from_rtx) == VOIDmode));
+
+  rtx temp = copy_to_mode_reg (mode, from_rtx);
+
+  rtvec argvec = rtvec_alloc (1);
+  rtvec constraintvec = rtvec_alloc (1);
+  rtvec labelvec = rtvec_alloc (0);
+
+  rtx body = gen_rtx_ASM_OPERANDS (mode,
+				   ggc_strdup (""),
+				   "", 0,
+				   argvec, constraintvec, labelvec,
+				   locus);
+  ASM_OPERANDS_INPUT (body, 0) = temp;
+  ASM_OPERANDS_INPUT_CONSTRAINT_EXP (body, 0)
+    = gen_rtx_ASM_INPUT_loc (mode, "0,0", locus);
+  ASM_OPERANDS_OUTPUT_CONSTRAINT (body) = "=^X,g";
+  emit_insn (gen_rtx_SET (temp, body));
+
+  emit_move_insn (to_rtx, temp);
+}
+
 /* Expand {MASK_,}SCATTER_STORE{S,U} call CALL using optab OPTAB.  */
 
 static void
diff --git a/gcc/internal-fn.def b/gcc/internal-fn.def
index bb4d8ab8096..4fcb84231fd 100644
--- a/gcc/internal-fn.def
+++ b/gcc/internal-fn.def
@@ -406,6 +406,10 @@ DEF_INTERNAL_FN (FALLTHROUGH, ECF_LEAF | ECF_NOTHROW, NULL)
 /* To implement __builtin_launder.  */
 DEF_INTERNAL_FN (LAUNDER, ECF_LEAF | ECF_NOTHROW | ECF_NOVOPS, NULL)
 
+/* Copy a value while preventing optimizations based on knowledge
+   about the input operand.  */
+DEF_INTERNAL_FN (ASMNESIA, ECF_LEAF | ECF_NOTHROW, NULL)
+
 /* Divmod function.  */
 DEF_INTERNAL_FN (DIVMOD, ECF_CONST | ECF_LEAF, NULL)