PR rtl-optimization/123833: Use of insn attributes in insn_costs corrupts recog_data.

Thanks again to Jeff Law and Andrew Pinski.  Here's a revised patch that
addresses the true underlying cause of PR 128333.  recog.cc's cancel_changes
was not correctly updating the recog_data cache, which leads to strange
(incorrect) behavior in fwprop and ifcvt.

2026-02-07  Roger Sayle  <roger@nextmovesoftware.com>
	    Andrew Pinski  <andrew.pinski@oss.qualcomm.com>
	    Jeff Law  <jeffrey.law@oss.qualcomm.com>

gcc/ChangeLog
	PR rtl-optimization/123833
	* recog.cc (cancel_changes): Update the recog_data cache if it
	holds the instruction being changed.

gcc/testsuite
	PR rtl-optimization/123833
	* gcc.target/mips/pr123833.c: New test case.

diff --git a/gcc/recog.cc b/gcc/recog.cc
index 48f6b45ec6d7029a35acc657e563cbc981621877..f37e548d6ab1bf04979f5f868e8568f8101a32ea 100644 (file)
--- a/gcc/recog.cc
+++ b/gcc/recog.cc
@@ -608,7 +608,11 @@ cancel_changes (int num)
       else
        *changes[i].loc = changes[i].old;
       if (changes[i].object && !MEM_P (changes[i].object))
-       INSN_CODE (changes[i].object) = changes[i].old_code;
+       {
+         INSN_CODE (changes[i].object) = changes[i].old_code;
+         if (recog_data.insn == changes[i].object)
+           recog_data.insn = nullptr;
+       }
     }
   num_changes = num;
 }

diff --git a/gcc/testsuite/gcc.target/mips/pr123833.c b/gcc/testsuite/gcc.target/mips/pr123833.c
new file mode 100644 (file)
index 0000000..4d0c9e8
--- /dev/null
+++ b/gcc/testsuite/gcc.target/mips/pr123833.c
@@ -0,0 +1,26 @@
+/* { dg-do compile } */
+/* { dg-options "-O1 -mabi=64 -mhard-float" } */
+
+typedef short int16_t;
+typedef signed char int8_t;
+typedef long long int64_t;
+typedef unsigned char uint8_t;
+typedef unsigned long long uint64_t;
+
+#define BS_VEC(type, num) type __attribute__((vector_size(num * sizeof(type))))
+BS_VEC(int8_t, 2) backsmith_pure_0(int64_t);
+uint64_t backsmith_pure_4(int16_t BS_ARG_0)
+{
+    BS_VEC(int16_t, 16)
+    BS_VAR_0 = __builtin_convertvector(
+        __builtin_shufflevector(backsmith_pure_0(0), backsmith_pure_0(0), 0, 2,
+                                2, 3, 2, 1, 2, 3, 0, 2, 0, 0, 2, 2, 0, 1),
+        BS_VEC(int16_t, 16));
+    for (;;)
+    {
+        if (__builtin_ctzg((uint8_t)BS_VAR_0[3], BS_ARG_0))
+            for (;;);
+        return 0;
+    }
+}
+