re PR target/36133 (GCC creates suboptimal ASM : Code includes unneeded TST instructions)

2008-11-19  Andrew Stubbs  <ams@codesourcery.com>

	gcc/
	PR target/36133
	* config/m68k/m68k.h (CC_OVERFLOW_UNUSABLE, CC_NO_CARRY): New defines.
	* config/m68k/m68k.c (notice_update_cc): Set cc_status properly for
	shift instructions.
	* config/m68k/m68k.md: Adjust all conditional branches that use the
	carry and overflow flags so they understand CC_OVERFLOW_UNUSABLE.

	gcc/testsuite/
	PR target/36133
	* gcc.target/m68k/pr36133.c: New test.

From-SVN: r141999

6 files changed, 159 insertions, 11 deletions

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index a32aa12..c1973fa 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,12 @@
+2008-11-19  Andrew Stubbs  <ams@codesourcery.com>
+
+	PR target/36133
+	* config/m68k/m68k.h (CC_OVERFLOW_UNUSABLE, CC_NO_CARRY): New defines.
+	* config/m68k/m68k.c (notice_update_cc): Set cc_status properly for
+	shift instructions.
+	* config/m68k/m68k.md: Adjust all conditional branches that use the
+	carry and overflow flags so they understand CC_OVERFLOW_UNUSABLE.
+
 2008-11-18  Uros Bizjak  <ubizjak@gmail.com>
 
 	PR target/37362
diff --git a/gcc/config/m68k/m68k.c b/gcc/config/m68k/m68k.c
index c762a8f..d8cc370 100644
--- a/gcc/config/m68k/m68k.c
+++ b/gcc/config/m68k/m68k.c
@@ -3605,9 +3605,7 @@ notice_update_cc (rtx exp, rtx insn)
       case ROTATE: case ROTATERT:
 	/* These instructions always clear the overflow bit, and set
 	   the carry to the bit shifted out.  */
-	/* ??? We don't currently have a way to signal carry not valid,
-	   nor do we check for it in the branch insns.  */
-	CC_STATUS_INIT;
+	cc_status.flags |= CC_OVERFLOW_UNUSABLE | CC_NO_CARRY;
 	break;
 
       case PLUS: case MINUS: case MULT:
diff --git a/gcc/config/m68k/m68k.h b/gcc/config/m68k/m68k.h
index 280f16d..8c0f4f2 100644
--- a/gcc/config/m68k/m68k.h
+++ b/gcc/config/m68k/m68k.h
@@ -855,6 +855,14 @@ __transfer_from_trampoline ()					\
    some or all of the saved cc's so they won't be used.  */
 #define NOTICE_UPDATE_CC(EXP,INSN) notice_update_cc (EXP, INSN)
 
+/* The shift instructions always clear the overflow bit.  */
+#define CC_OVERFLOW_UNUSABLE 01000
+
+/* The shift instructions use the carry bit in a way not compatible with
+   conditional branches.  conditions.h uses CC_NO_OVERFLOW for this purpose.
+   Rename it to something more understandable.  */
+#define CC_NO_CARRY CC_NO_OVERFLOW
+
 #define OUTPUT_JUMP(NORMAL, FLOAT, NO_OV)  \
 do { if (cc_prev_status.flags & CC_IN_68881)			\
     return FLOAT;						\
diff --git a/gcc/config/m68k/m68k.md b/gcc/config/m68k/m68k.md
index cf3e120..75f36dc 100644
--- a/gcc/config/m68k/m68k.md
+++ b/gcc/config/m68k/m68k.md
@@ -6371,6 +6371,12 @@
 		      (pc)))]
   ""
 {
+  if ((cc_status.flags & CC_OVERFLOW_UNUSABLE) != 0)
+    {
+      cc_status.flags &= ~CC_OVERFLOW_UNUSABLE;
+      return 0;
+    }
+
   OUTPUT_JUMP ("jgt %l0", "fjgt %l0", 0);
 }
   [(set (attr "type") (symbol_ref "m68k_sched_branch_type (insn)"))])
@@ -6382,7 +6388,15 @@
 		      (label_ref (match_operand 0 "" ""))
 		      (pc)))]
   ""
-  "jhi %l0"
+{
+  if ((cc_status.flags & CC_OVERFLOW_UNUSABLE) != 0)
+    {
+      cc_status.flags &= ~CC_OVERFLOW_UNUSABLE;
+      return 0;
+    }
+
+  return "jhi %l0";
+}
   [(set_attr "type" "bcc")])
 
 (define_insn "blt"
@@ -6393,6 +6407,12 @@
 		      (pc)))]
   ""
 {
+  if ((cc_status.flags & CC_OVERFLOW_UNUSABLE) != 0)
+    {
+      cc_status.flags &= ~CC_OVERFLOW_UNUSABLE;
+      return 0;
+    }
+
   OUTPUT_JUMP ("jlt %l0", "fjlt %l0", "jmi %l0");
 }
   [(set (attr "type") (symbol_ref "m68k_sched_branch_type (insn)"))])
@@ -6404,7 +6424,15 @@
 		      (label_ref (match_operand 0 "" ""))
 		      (pc)))]
   ""
-  "jcs %l0"
+{
+  if ((cc_status.flags & CC_OVERFLOW_UNUSABLE) != 0)
+    {
+      cc_status.flags &= ~CC_OVERFLOW_UNUSABLE;
+      return 0;
+    }
+
+  return "jcs %l0";
+}
   [(set_attr "type" "bcc")])
 
 (define_insn "bge"
@@ -6415,6 +6443,12 @@
 		      (pc)))]
   ""
 {
+  if ((cc_status.flags & CC_OVERFLOW_UNUSABLE) != 0)
+    {
+      cc_status.flags &= ~CC_OVERFLOW_UNUSABLE;
+      return 0;
+    }
+
   OUTPUT_JUMP ("jge %l0", "fjge %l0", "jpl %l0");
 })
 
@@ -6425,7 +6459,15 @@
 		      (label_ref (match_operand 0 "" ""))
 		      (pc)))]
   ""
-  "jcc %l0"
+{
+  if ((cc_status.flags & CC_OVERFLOW_UNUSABLE) != 0)
+    {
+      cc_status.flags &= ~CC_OVERFLOW_UNUSABLE;
+      return 0;
+    }
+
+  return "jcc %l0";
+}
   [(set_attr "type" "bcc")])
 
 (define_insn "ble"
@@ -6436,6 +6478,12 @@
 		      (pc)))]
   ""
 {
+  if ((cc_status.flags & CC_OVERFLOW_UNUSABLE) != 0)
+    {
+      cc_status.flags &= ~CC_OVERFLOW_UNUSABLE;
+      return 0;
+    }
+
   OUTPUT_JUMP ("jle %l0", "fjle %l0", 0);
 }
   [(set_attr "type" "bcc")])
@@ -6447,7 +6495,15 @@
 		      (label_ref (match_operand 0 "" ""))
 		      (pc)))]
   ""
-  "jls %l0"
+{
+  if ((cc_status.flags & CC_OVERFLOW_UNUSABLE) != 0)
+    {
+      cc_status.flags &= ~CC_OVERFLOW_UNUSABLE;
+      return 0;
+    }
+
+  return "jls %l0";
+}
   [(set_attr "type" "bcc")])
 
 (define_insn "bordered"
@@ -6580,6 +6636,12 @@
 		      (label_ref (match_operand 0 "" ""))))]
   ""
 {
+  if ((cc_status.flags & CC_OVERFLOW_UNUSABLE) != 0)
+    {
+      cc_status.flags &= ~CC_OVERFLOW_UNUSABLE;
+      return 0;
+    }
+
   OUTPUT_JUMP ("jle %l0", "fjngt %l0", 0);
 }
   [(set_attr "type" "bcc")])
@@ -6591,7 +6653,15 @@
 		      (pc)
 		      (label_ref (match_operand 0 "" ""))))]
   ""
-  "jls %l0"
+{
+  if ((cc_status.flags & CC_OVERFLOW_UNUSABLE) != 0)
+    {
+      cc_status.flags &= ~CC_OVERFLOW_UNUSABLE;
+      return 0;
+    }
+
+  return "jls %l0";
+}
   [(set_attr "type" "bcc")])
 
 (define_insn "*blt_rev"
@@ -6602,6 +6672,12 @@
 		      (label_ref (match_operand 0 "" ""))))]
   ""
 {
+  if ((cc_status.flags & CC_OVERFLOW_UNUSABLE) != 0)
+    {
+      cc_status.flags &= ~CC_OVERFLOW_UNUSABLE;
+      return 0;
+    }
+
   OUTPUT_JUMP ("jge %l0", "fjnlt %l0", "jpl %l0");
 }
   [(set_attr "type" "bcc")])
@@ -6613,7 +6689,15 @@
 		      (pc)
 		      (label_ref (match_operand 0 "" ""))))]
   ""
-  "jcc %l0"
+{
+  if ((cc_status.flags & CC_OVERFLOW_UNUSABLE) != 0)
+    {
+      cc_status.flags &= ~CC_OVERFLOW_UNUSABLE;
+      return 0;
+    }
+
+  return "jcc %l0";
+}
   [(set_attr "type" "bcc")])
 
 (define_insn "*bge_rev"
@@ -6624,6 +6708,12 @@
 		      (label_ref (match_operand 0 "" ""))))]
   ""
 {
+  if ((cc_status.flags & CC_OVERFLOW_UNUSABLE) != 0)
+    {
+      cc_status.flags &= ~CC_OVERFLOW_UNUSABLE;
+      return 0;
+    }
+
   OUTPUT_JUMP ("jlt %l0", "fjnge %l0", "jmi %l0");
 }
   [(set_attr "type" "bcc")])
@@ -6635,7 +6725,15 @@
 		      (pc)
 		      (label_ref (match_operand 0 "" ""))))]
   ""
-  "jcs %l0"
+{
+  if ((cc_status.flags & CC_OVERFLOW_UNUSABLE) != 0)
+    {
+      cc_status.flags &= ~CC_OVERFLOW_UNUSABLE;
+      return 0;
+    }
+
+  return "jcs %l0";
+}
   [(set_attr "type" "bcc")])
 
 (define_insn "*ble_rev"
@@ -6646,6 +6744,12 @@
 		      (label_ref (match_operand 0 "" ""))))]
   ""
 {
+  if ((cc_status.flags & CC_OVERFLOW_UNUSABLE) != 0)
+    {
+      cc_status.flags &= ~CC_OVERFLOW_UNUSABLE;
+      return 0;
+    }
+
   OUTPUT_JUMP ("jgt %l0", "fjnle %l0", 0);
 }
   [(set_attr "type" "bcc")])
@@ -6657,7 +6761,15 @@
 		      (pc)
 		      (label_ref (match_operand 0 "" ""))))]
   ""
-  "jhi %l0"
+{
+  if ((cc_status.flags & CC_OVERFLOW_UNUSABLE) != 0)
+    {
+      cc_status.flags &= ~CC_OVERFLOW_UNUSABLE;
+      return 0;
+    }
+
+  return "jhi %l0";
+}
   [(set_attr "type" "bcc")])
 
 (define_insn "*bordered_rev"
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index 5a80bd2..354eda6 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,8 @@
+2008-11-19  Andrew Stubbs  <ams@codesourcery.com>
+
+	PR target/36133
+	* gcc.target/m68k/pr36133.c: New test.
+
 2008-11-19  Maxim Kuvyrkov  <maxim@codesourcery.com>
   
  	* gcc.gd/struct/wo_prof_global_var.c: Use uninitialized integer
diff --git a/gcc/testsuite/gcc.target/m68k/pr36133.c b/gcc/testsuite/gcc.target/m68k/pr36133.c
new file mode 100644
index 0000000..25237a8
--- /dev/null
+++ b/gcc/testsuite/gcc.target/m68k/pr36133.c
@@ -0,0 +1,16 @@
+/* pr36133.c
+
+   This test ensures that conditional branches can use the condition codes
+   written by shift instructions, without the need for an extra TST.  */
+
+/* { dg-do compile }  */
+/* { dg-options "-O2" }  */
+/* { dg-final { scan-assembler-not "tst" } } */
+
+void
+f (unsigned int a)
+{
+  if (a >> 4)
+    asm volatile ("nop");
+  asm volatile ("nop");
+}