[PATCH] Handle truncate of a memory location

[Andrew Pinski]

Hi,
  A truncate of a memory location can be simplified to a memory load
just like what is done for a subreg of a memory load.
This patch adds that simplification to simplify-rtx.c.

OK? Bootstrapped and tested on mips64-linux-gnu with no regressions.

Thanks,
Andrew Pinski

ChangeLog:

* simplify-rtx.c (simplify_unary_operation_1 <case TRUNCATE>):
A truncate of a memory is just loading the low part of the memory.

testsuite/ChangeLog:
* gcc.target/mips/truncate-8.c: New testcase.

Index: simplify-rtx.c
===================================================================
--- simplify-rtx.c      (revision 190730)
+++ simplify-rtx.c      (working copy)
@@ -869,6 +869,14 @@ simplify_unary_operation_1 (enum rtx_cod
          && COMPARISON_P (op)
          && (STORE_FLAG_VALUE & ~GET_MODE_MASK (mode)) == 0)
        return rtl_hooks.gen_lowpart_no_emit (mode, op);
+
+      /* A truncate of a memory is just loading the low part of the memory
+        if are not changing the meaning of the address. */
+      if (GET_CODE (op) == MEM
+         && !MEM_VOLATILE_P (op)
+         && !mode_dependent_address_p (XEXP (op, 0)))
+       return rtl_hooks.gen_lowpart_no_emit (mode, op);
+
       break;
 
     case FLOAT_TRUNCATE:
Index: testsuite/gcc.target/mips/truncate-8.c
===================================================================
--- testsuite/gcc.target/mips/truncate-8.c      (revision 0)
+++ testsuite/gcc.target/mips/truncate-8.c      (revision 0)
@@ -0,0 +1,17 @@
+/* { dg-options "-mgp64" } */
+/* { dg-skip-if "code quality test" { *-*-* } { "-O0" } { "" } } */
+/* { dg-final { scan-assembler "lw\t" } } */
+/* { dg-final { scan-assembler-not "sll" } } */
+
+struct s
+{
+  long long a;
+  int b;
+};
+
+int
+foo (struct s *x)
+{
+  return x->a;
+}
+