tcg/optimize: Do not attempt to constant fold neg_vec

Split out the tail of fold_neg to fold_neg_no_const so that we
can avoid attempting to constant fold vector negate.

Resolves: https://gitlab.com/qemu-project/qemu/-/issues/2150
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

tcg/optimize.c

@@ -1990,16 +1990,10 @@ static bool fold_nand(OptContext *ctx, TCGOp *op)
     return false;
 }
 
-static bool fold_neg(OptContext *ctx, TCGOp *op)
+static bool fold_neg_no_const(OptContext *ctx, TCGOp *op)
 {
-    uint64_t z_mask;
-
-    if (fold_const1(ctx, op)) {
-        return true;
-    }
-
     /* Set to 1 all bits to the left of the rightmost.  */
-    z_mask = arg_info(op->args[1])->z_mask;
+    uint64_t z_mask = arg_info(op->args[1])->z_mask;
     ctx->z_mask = -(z_mask & -z_mask);
 
     /*
@@ -2010,6 +2004,11 @@ static bool fold_neg(OptContext *ctx, TCGOp *op)
     return true;
 }
 
+static bool fold_neg(OptContext *ctx, TCGOp *op)
+{
+    return fold_const1(ctx, op) || fold_neg_no_const(ctx, op);
+}
+
 static bool fold_nor(OptContext *ctx, TCGOp *op)
 {
     if (fold_const2_commutative(ctx, op) ||
@@ -2418,7 +2417,7 @@ static bool fold_sub_to_neg(OptContext *ctx, TCGOp *op)
     if (have_neg) {
         op->opc = neg_op;
         op->args[1] = op->args[2];
-        return fold_neg(ctx, op);
+        return fold_neg_no_const(ctx, op);
     }
     return false;
 }

tests/tcg/aarch64/Makefile.target

@@ -10,7 +10,7 @@ VPATH 		+= $(AARCH64_SRC)
 
 # Base architecture tests
 AARCH64_TESTS=fcvt pcalign-a64 lse2-fault
-AARCH64_TESTS += test-2248
+AARCH64_TESTS += test-2248 test-2150
 
 fcvt: LDFLAGS+=-lm
 

tests/tcg/aarch64/test-2150.c

@@ -0,0 +1,12 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/* See https://gitlab.com/qemu-project/qemu/-/issues/2150 */
+
+int main()
+{
+    asm volatile(
+        "movi     v6.4s, #1\n"
+        "movi     v7.4s, #0\n"
+        "sub      v6.2d, v7.2d, v6.2d\n"
+        : : : "v6", "v7");
+    return 0;
+}