LoongArch: Fix ICE when trying to recognize bitwise + alsl.w pair [PR119127]

When we call loongarch_reassoc_shift_bitwise for
<optab>_alsl_reversesi_extend, the mask is in DImode but we are trying
to operate it in SImode, causing an ICE.

To fix the issue sign-extend the mask into the mode we want.  And also
specially handle the case the mask is extended into -1 to avoid a
miss-optimization.

gcc/ChangeLog:

	PR target/119127
	* config/loongarch/loongarch.cc
	(loongarch_reassoc_shift_bitwise): Sign extend mask to mode,
	specially handle the case it's extended to -1.
	* config/loongarch/loongarch.md
	(loongarch_reassoc_shift_bitwise): Update the comment for the
	special case.

3 files changed, 31 insertions, 11 deletions

diff --git a/gcc/config/loongarch/loongarch.cc b/gcc/config/loongarch/loongarch.cc
index 68f5d85..01f0486 100644
--- a/gcc/config/loongarch/loongarch.cc
+++ b/gcc/config/loongarch/loongarch.cc
@@ -4575,8 +4575,22 @@ loongarch_reassoc_shift_bitwise (bool is_and, rtx shamt, rtx mask,
   if (ctz_hwi (INTVAL (mask)) < INTVAL (shamt))
     return NULL_RTX;
 
+  /* When trying alsl.w, deliberately ignore the high bits.  */
+  mask = gen_int_mode (UINTVAL (mask), mode);
+
   rtx new_mask = simplify_const_binary_operation (LSHIFTRT, mode, mask,
 						  shamt);
+
+  /* Do an arithmetic shift for checking ins_zero_bitmask_operand or -1:
+     ashiftrt (0xffffffff00000000, 2) is 0xffffffff60000000 which is an
+     ins_zero_bitmask_operand, but lshiftrt will produce
+     0x3fffffff60000000.  */
+  rtx new_mask_1 = simplify_const_binary_operation (ASHIFTRT, mode, mask,
+						    shamt);
+
+  if (is_and && const_m1_operand (new_mask_1, mode))
+    return new_mask_1;
+
   if (const_uns_arith_operand (new_mask, mode))
     return new_mask;
 
@@ -4586,13 +4600,7 @@ loongarch_reassoc_shift_bitwise (bool is_and, rtx shamt, rtx mask,
   if (low_bitmask_operand (new_mask, mode))
     return new_mask;
 
-  /* Do an arithmetic shift for checking ins_zero_bitmask_operand:
-     ashiftrt (0xffffffff00000000, 2) is 0xffffffff60000000 which is an
-     ins_zero_bitmask_operand, but lshiftrt will produce
-     0x3fffffff60000000.  */
-  new_mask = simplify_const_binary_operation (ASHIFTRT, mode, mask,
-					      shamt);
-  return ins_zero_bitmask_operand (new_mask, mode) ? new_mask : NULL_RTX;
+  return ins_zero_bitmask_operand (new_mask_1, mode) ? new_mask_1 : NULL_RTX;
 }
 
 /* Implement TARGET_CONSTANT_ALIGNMENT.  */
diff --git a/gcc/config/loongarch/loongarch.md b/gcc/config/loongarch/loongarch.md
index 90c475e..f7005de 100644
--- a/gcc/config/loongarch/loongarch.md
+++ b/gcc/config/loongarch/loongarch.md
@@ -3200,10 +3200,8 @@
       emit_insn (gen_<optab>di3 (operands[0], operands[1], operands[3]));
     else
       {
-	/* Hmm would we really reach here?  If we reach here we'd have
-	   a miss-optimization in the generic code (as it should have
-	   optimized this to alslsi3_extend_subreg).  But let's be safe
-	   than sorry.  */
+	/* We can end up here with things like:
+	   x:DI = sign_extend(a:SI + ((b:DI << 2) & 0xfffffffc)#0)  */
 	gcc_checking_assert (<is_and>);
 	emit_move_insn (operands[0], operands[1]);
       }
diff --git a/gcc/testsuite/gcc.target/loongarch/pr119127.c b/gcc/testsuite/gcc.target/loongarch/pr119127.c
new file mode 100644
index 0000000..4e253be
--- /dev/null
+++ b/gcc/testsuite/gcc.target/loongarch/pr119127.c
@@ -0,0 +1,14 @@
+/* PR target/119127: ICE caused by operating DImode const in SImode */
+/* { dg-do compile } */
+/* { dg-options "-O2 -march=loongarch64 -mabi=lp64d" } */
+
+int x;
+struct Type {
+  unsigned SubclassData : 24;
+} y;
+
+void
+test (void)
+{
+  x = y.SubclassData * 37;
+}