Re: [Patch, MIPS] Patch to fix MIPS optimization bug in combine

[Steve Ellcey <sellcey at imgtec dot com>]

Andrew,

Here is the new patch that I am currently testing with your change and
incorporating Eric's comment.  I included both test cases but renamed
yours and put it into gcc.dg/torture.  Does the code in combine.c to
address Eric's comment look OK to you?

Steve Ellcey
steve.ellcey@imgtec.com


2015-10-21  Steve Ellcey  <sellcey@imgtec.com>
	    Andrew Pinski  <apinski@cavium.com>

	* combine.c (simplify_comparison): Use gen_lowpart_or_truncate instead
	of gen_lowpart when we had a truncating and.


diff --git a/gcc/combine.c b/gcc/combine.c
index fd3e19c..7568ebb 100644
--- a/gcc/combine.c
+++ b/gcc/combine.c
@@ -11529,8 +11529,8 @@ simplify_comparison (enum rtx_code code, rtx *pop0, rtx *pop1)
 		 tmode != GET_MODE (op0); tmode = GET_MODE_WIDER_MODE (tmode))
 	      if ((unsigned HOST_WIDE_INT) c0 == GET_MODE_MASK (tmode))
 		{
-		  op0 = gen_lowpart (tmode, inner_op0);
-		  op1 = gen_lowpart (tmode, inner_op1);
+		  op0 = gen_lowpart_or_truncate (tmode, inner_op0);
+		  op1 = gen_lowpart_or_truncate (tmode, inner_op1);
 		  code = unsigned_condition (code);
 		  changed = 1;
 		  break;
@@ -12048,12 +12048,9 @@ simplify_comparison (enum rtx_code code, rtx *pop0, rtx *pop1)
 				   & GET_MODE_MASK (mode))
 				  + 1)) >= 0
 	      && const_op >> i == 0
-	      && (tmode = mode_for_size (i, MODE_INT, 1)) != BLKmode
-	      && (TRULY_NOOP_TRUNCATION_MODES_P (tmode, GET_MODE (op0))
-		  || (REG_P (XEXP (op0, 0))
-		      && reg_truncated_to_mode (tmode, XEXP (op0, 0)))))
+	      && (tmode = mode_for_size (i, MODE_INT, 1)) != BLKmode)
 	    {
-	      op0 = gen_lowpart (tmode, XEXP (op0, 0));
+	      op0 = gen_lowpart_or_truncate (tmode, XEXP (op0, 0));
 	      continue;
 	    }
 

2015-10-21  Steve Ellcey  <sellcey@imgtec.com>
	    Andrew Pinski  <apinski@cavium.com>

	* gcc.dg/torture/pr67736.c: New test.
	* gcc.dg/combine-subregs.c: New test.

diff --git a/gcc/testsuite/gcc.dg/combine-subregs.c b/gcc/testsuite/gcc.dg/combine-subregs.c
index e69de29..c480f88 100644
--- a/gcc/testsuite/gcc.dg/combine-subregs.c
+++ b/gcc/testsuite/gcc.dg/combine-subregs.c
@@ -0,0 +1,36 @@
+/* { dg-do run } */
+/* { dg-options "-O2 -fexpensive-optimizations" } */
+
+#include <inttypes.h>
+#include <stdlib.h>
+
+void __attribute__ ((noinline))
+foo (uint64_t state, uint32_t last)
+{
+  if (state == last) abort ();
+}
+
+/* This function may do a bad comparision by trying to
+   use SUBREGS during the compare on machines where comparing
+   two registers always compares the entire register regardless
+   of mode.  */
+
+int __attribute__ ((noinline))
+compare (uint64_t state, uint32_t *last, uint8_t buf)
+{
+    if (*last == ((state | buf) & 0xFFFFFFFF)) {
+	foo (state, *last);
+        return 0;
+    }
+    return 1;
+}
+
+int
+main(int argc, char **argv) {
+    uint64_t state = 0xF00000100U;
+    uint32_t last  = 0x101U;
+    int ret        = compare(state, &last, 0x01);
+    if (ret != 0)
+	abort ();
+    exit (0);
+}
diff --git a/gcc/testsuite/gcc.dg/torture/pr67736.c b/gcc/testsuite/gcc.dg/torture/pr67736.c
index e69de29..b45874e 100644
--- a/gcc/testsuite/gcc.dg/torture/pr67736.c
+++ b/gcc/testsuite/gcc.dg/torture/pr67736.c
@@ -0,0 +1,32 @@
+/* { dg-do run } */
+
+#include <stdlib.h>
+
+typedef unsigned long long uint64_t;
+void f(uint64_t *a, uint64_t aa) __attribute__((noinline));
+void f(uint64_t *a, uint64_t aa)
+{
+  uint64_t new_value = aa;
+  uint64_t old_value = *a;
+  int bit_size = 32;
+    uint64_t mask = (uint64_t)(unsigned)(-1);
+    uint64_t tmp = old_value & mask;
+    new_value &= mask;
+    /* On overflow we need to add 1 in the upper bits */
+    if (tmp > new_value)
+        new_value += 1ull<<bit_size;
+    /* Add in the upper bits from the old value */
+    new_value += old_value & ~mask;
+    *a = new_value;
+}
+int main(void)
+{
+  uint64_t value, new_value, old_value;
+  value = 0x100000001;
+  old_value = value;
+  new_value = (value+1)&(uint64_t)(unsigned)(-1);
+  f(&value, new_value);
+  if (value != old_value+1)
+    __builtin_abort ();
+  return 0;
+}