[PATCH] combine: Don't simplify paradoxical SUBREG on WORD_REGISTER_OPERATIONS [PR113010]

The sign-bit-copies of a sign-extending load cannot be known until runtime on
WORD_REGISTER_OPERATIONS targets, except in the case of a zero-extending MEM
load.  See the fix for PR112758.

gcc/
	PR rtl-optimization/113010
	* combine.cc (simplify_comparison): Simplify a SUBREG on
	WORD_REGISTER_OPERATIONS targets only if it is a zero-extending
	MEM load.

gcc/testsuite
	* gcc.c-torture/execute/pr113010.c: New test.

diff --git a/gcc/combine.cc b/gcc/combine.cc
index 76543d85b7c8ba3b591b64a29a9d205ea973bc6a..b09200d757e2b9a41455b2b9d925984e1f61e72c 100644 (file)
--- a/gcc/combine.cc
+++ b/gcc/combine.cc
@@ -12550,9 +12550,20 @@ simplify_comparison (enum rtx_code code, rtx *pop0, rtx *pop1)
            }
 
          /* If the inner mode is narrower and we are extracting the low part,
-            we can treat the SUBREG as if it were a ZERO_EXTEND.  */
+            we can treat the SUBREG as if it were a ZERO_EXTEND ...  */
          if (paradoxical_subreg_p (op0))
-           ;
+           {
+             if (WORD_REGISTER_OPERATIONS
+                 && GET_MODE_PRECISION (inner_mode) < BITS_PER_WORD
+                 /* On WORD_REGISTER_OPERATIONS targets the bits
+                    beyond sub_mode aren't considered undefined,
+                    so optimize only if it is a MEM load when MEM loads
+                    zero extend, because then the upper bits are all zero.  */
+                 && !(MEM_P (SUBREG_REG (op0))
+                      && load_extend_op (inner_mode) == ZERO_EXTEND))
+               break;
+             /* FALLTHROUGH to case ZERO_EXTEND */
+           }
          else if (subreg_lowpart_p (op0)
                   && GET_MODE_CLASS (mode) == MODE_INT
                   && is_int_mode (GET_MODE (SUBREG_REG (op0)), &inner_mode)

diff --git a/gcc/testsuite/gcc.c-torture/execute/pr113010.c b/gcc/testsuite/gcc.c-torture/execute/pr113010.c
new file mode 100644 (file)
index 0000000..2c84333
--- /dev/null
+++ b/gcc/testsuite/gcc.c-torture/execute/pr113010.c
@@ -0,0 +1,9 @@
+int minus_1 = -1;
+
+int
+main ()
+{
+  if ((0, 0xffffffffull) >= minus_1)
+    __builtin_abort ();
+  return 0;
+}