[PATCH][2/2] Fix PR81502

[Richard Biener]

I am testing the following additional pattern for match.pd to fix
PR81502 resulting in the desired optimization to

bar:
.LFB526:
        .cfi_startproc
        movl    %edi, %eax
        ret

the pattern optimizes a BIT_FIELD_REF on a BIT_INSERT_EXPR by
either extracting from the destination or the inserted value.

Bootstrap and regtest running on x86_64-unknown-linux-gnu.

Richard.

2017-07-27  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/81502
	* match.pd: Add pattern combining BIT_INSERT_EXPR with
	BIT_FIELD_REF.

	* gcc.target/i386/pr81502.c: New testcase.

Index: gcc/match.pd
===================================================================
*** gcc/match.pd	(revision 250620)
--- gcc/match.pd	(working copy)
*************** DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
*** 4178,4180 ****
--- 4178,4195 ----
  	 { CONSTRUCTOR_ELT (ctor, idx / k)->value; })
  	(BIT_FIELD_REF { CONSTRUCTOR_ELT (ctor, idx / k)->value; }
  		       @1 { bitsize_int ((idx % k) * width); })))))))))
+ 
+ /* Simplify a bit extraction from a bit insertion for the cases with
+    the inserted element fully covering the extraction or the insertion
+    not touching the extraction.  */
+ (simplify
+  (BIT_FIELD_REF (bit_insert @0 @1 @ipos) @rsize @rpos)
+  (switch
+   (if (wi::leu_p (@ipos, @rpos)
+        && wi::leu_p (wi::add (@rpos, @rsize),
+                      wi::add (@ipos, TYPE_PRECISION (TREE_TYPE (@1)))))
+    (BIT_FIELD_REF @1 @rsize { wide_int_to_tree (bitsizetype,
+                                                 wi::sub (@rpos, @ipos)); }))
+   (if (wi::geu_p (@ipos, wi::add (@rpos, @rsize))
+        || wi::geu_p (@rpos, wi::add (@ipos, TYPE_PRECISION (TREE_TYPE (@1)))))
+    (BIT_FIELD_REF @0 @rsize @rpos))))
Index: gcc/testsuite/gcc.target/i386/pr81502.c
===================================================================
*** gcc/testsuite/gcc.target/i386/pr81502.c	(nonexistent)
--- gcc/testsuite/gcc.target/i386/pr81502.c	(working copy)
***************
*** 0 ****
--- 1,34 ----
+ /* { dg-do compile { target lp64 } } */
+ /* { dg-options "-O2 -msse2" } */
+ 
+ #include <emmintrin.h>
+ 
+ #define SIZE (sizeof (void *))
+ 
+ static int foo(unsigned char (*foo)[SIZE])
+ {
+   __m128i acc = _mm_set_epi32(0, 0, 0, 0);
+   size_t i = 0;
+   for(; i + sizeof(__m128i) <= SIZE; i += sizeof(__m128i)) {
+       __m128i word;
+       __builtin_memcpy(&word, foo + i, sizeof(__m128i));
+       acc = _mm_add_epi32(word, acc);
+   }
+   if (i != SIZE) {
+       __m128i word = _mm_set_epi32(0, 0, 0, 0);
+       __builtin_memcpy(&word, foo + i, SIZE - i); // (1)
+       acc = _mm_add_epi32(word, acc);
+   }
+   int res;
+   __builtin_memcpy(&res, &acc, sizeof(res));
+   return res;
+ }
+ 
+ int bar(void *ptr)
+ {
+   unsigned char buf[SIZE];
+   __builtin_memcpy(buf, &ptr, SIZE);
+   return foo((unsigned char(*)[SIZE])buf);
+ }
+ 
+ /* { dg-final { scan-assembler-times "mov" 1 } } */