[PATCH 1/2] simplify-rtx: Simplify trunc of and of shiftrt

[Segher Boessenkool]

If we have

        (truncate:M1 (and:M2 (lshiftrt:M2 (x:M2) C) C2))

we can write it instead as

        (and:M1 (lshiftrt:M1 (truncate:M1 (x:M2)) C) C2)

(if that is valid, of course), which has smaller modes for the
binary ops, and the truncate can often simplify further (if "x"
is a register, for example).

This fixes gcc.target/powerpc/20050603-3.c for -m32 -mpowerpc64;
also that test is currently restricted to ilp32, but we can run
it with lp64 just fine, in which case it fixes that, too.

Bootstrapped and tested on powerpc64-linux (-m32,-m32/-mpowerpc64,-m64).
Is this okay for trunk?


Segher


2015-11-09  Segher Boessenkool  <seg...@kernel.crashing.org>

        * gcc/simplify-rtx.c (simplify_truncation): Simplify TRUNCATE
        of AND of [LA]SHIFTRT.

---
 gcc/simplify-rtx.c | 25 +++++++++++++++++++++++++
 1 file changed, 25 insertions(+)

diff --git a/gcc/simplify-rtx.c b/gcc/simplify-rtx.c
index 17568ba..1adb393 100644
--- a/gcc/simplify-rtx.c
+++ b/gcc/simplify-rtx.c
@@ -714,6 +714,31 @@ simplify_truncation (machine_mode mode, rtx op,
     return simplify_gen_binary (ASHIFT, mode,
                                XEXP (XEXP (op, 0), 0), XEXP (op, 1));
 
+  /* Likewise (truncate:QI (and:SI (lshiftrt:SI (x:SI) C) C2)) into
+     (and:QI (lshiftrt:QI (truncate:QI (x:SI)) C) C2) for suitable C
+     and C2.  */
+  if (GET_CODE (op) == AND
+      && (GET_CODE (XEXP (op, 0)) == LSHIFTRT
+         || GET_CODE (XEXP (op, 0)) == ASHIFTRT)
+      && CONST_INT_P (XEXP (XEXP (op, 0), 1))
+      && CONST_INT_P (XEXP (op, 1))
+      && UINTVAL (XEXP (XEXP (op, 0), 1)) < precision
+      && ((GET_MODE_MASK (mode) >> UINTVAL (XEXP (XEXP (op, 0), 1)))
+         & UINTVAL (XEXP (op, 1)))
+        == ((GET_MODE_MASK (op_mode) >> UINTVAL (XEXP (XEXP (op, 0), 1)))
+            & UINTVAL (XEXP (op, 1))))
+    {
+      rtx op0 = simplify_gen_unary (TRUNCATE, mode, XEXP (XEXP (op, 0), 0),
+                                   op_mode);
+      if (op0)
+       {
+         op0 = simplify_gen_binary (LSHIFTRT, mode, op0,
+                                    XEXP (XEXP (op, 0), 1));
+         if (op0)
+           return simplify_gen_binary (AND, mode, op0, XEXP (op, 1));
+       }
+    }
+
   /* Recognize a word extraction from a multi-word subreg.  */
   if ((GET_CODE (op) == LSHIFTRT
        || GET_CODE (op) == ASHIFTRT)
-- 
1.9.3