[llvm-commits] [llvm] r45120 - in /llvm/trunk: include/llvm/Target/TargetInstrInfo.h lib/Target/Target.td
Bill Wendling
isanbard at gmail.com
Mon Dec 17 13:02:07 PST 2007
Author: void
Date: Mon Dec 17 15:02:07 2007
New Revision: 45120
URL: http://llvm.org/viewvc/llvm-project?rev=45120&view=rev
Log:
As per feedback, revised comments to (hopefully) make the different side effect
flags clearer.
Modified:
llvm/trunk/include/llvm/Target/TargetInstrInfo.h
llvm/trunk/lib/Target/Target.td
Modified: llvm/trunk/include/llvm/Target/TargetInstrInfo.h
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/Target/TargetInstrInfo.h?rev=45120&r1=45119&r2=45120&view=diff
==============================================================================
--- llvm/trunk/include/llvm/Target/TargetInstrInfo.h (original)
+++ llvm/trunk/include/llvm/Target/TargetInstrInfo.h Mon Dec 17 15:02:07 2007
@@ -91,17 +91,23 @@
// ARM instructions which can set condition code if 's' bit is set.
const unsigned M_HAS_OPTIONAL_DEF = 1 << 17;
-// M_MAY_HAVE_SIDE_EFFECTS - Set if this instruction *might* have side effects,
-// e.g. load instructions. Note: This and M_NEVER_HAS_SIDE_EFFECTS are mutually
-// exclusive. You can't set both! If neither flag is set, then the instruction
-// *always* has side effects.
-const unsigned M_MAY_HAVE_SIDE_EFFECTS = 1 << 18;
-
-// M_NEVER_HAS_SIDE_EFFECTS - Set if this instruction *never* has side effects,
-// e.g., xor on X86. Note: This and M_MAY_HAVE_SIDE_EFFECTS are mutually
-// exclusive. You can't set both! If neither flag is set, then the instruction
-// *always* has side effects.
-const unsigned M_NEVER_HAS_SIDE_EFFECTS = 1 << 19;
+// M_NEVER_HAS_SIDE_EFFECTS - Set if this instruction has no side effects that
+// are not captured by any operands of the instruction or other flags, and when
+// *all* instances of the instruction of that opcode have no side effects.
+//
+// Note: This and M_MAY_HAVE_SIDE_EFFECTS are mutually exclusive. You can't set
+// both! If neither flag is set, then the instruction *always* has side effects.
+const unsigned M_NEVER_HAS_SIDE_EFFECTS = 1 << 18;
+
+// M_MAY_HAVE_SIDE_EFFECTS - Set if some instances of this instruction can have
+// side effects. The virtual method "isReallySideEffectFree" is called to
+// determine this. Load instructions are an example of where this is useful. In
+// general, loads always have side effects. However, loads from constant pools
+// don't. We let the specific back end make this determination.
+//
+// Note: This and M_NEVER_HAS_SIDE_EFFECTS are mutually exclusive. You can't set
+// both! If neither flag is set, then the instruction *always* has side effects.
+const unsigned M_MAY_HAVE_SIDE_EFFECTS = 1 << 19;
// Machine operand flags
// M_LOOK_UP_PTR_REG_CLASS - Set if this operand is a pointer value and it
@@ -321,6 +327,15 @@
return true;
}
+ /// isReallySideEffectFree - If the M_MAY_HAVE_SIDE_EFFECTS flag is set, this
+ /// method is called to determine if the specific instance of this
+ /// instructions has side effects. This is useful in cases of instructions,
+ /// like loads, which generally always have side effects. A load from a
+ /// constant pool doesn't have side effects, though. So we need to
+ /// differentiate it from the general case.
+ virtual bool isReallySideEffectFree(MachineInstr *MI) const {
+ return false;
+ }
public:
/// getOperandConstraint - Returns the value of the specific constraint if
/// it is set. Returns -1 if it is not set.
Modified: llvm/trunk/lib/Target/Target.td
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/Target.td?rev=45120&r1=45119&r2=45120&view=diff
==============================================================================
--- llvm/trunk/lib/Target/Target.td (original)
+++ llvm/trunk/lib/Target/Target.td Mon Dec 17 15:02:07 2007
@@ -205,9 +205,18 @@
bit isNotDuplicable = 0; // Is it unsafe to duplicate this instruction?
// Side effect flags - If neither of these flags is set, then the instruction
- // *always* has side effects. Otherwise, it's one or the other.
- bit mayHaveSideEffects = 0; // This instruction *may* have side effects.
- bit neverHasSideEffects = 0; // This instruction never has side effects.
+ // *always* has side effects. When set, the flags have these meanings:
+ //
+ // neverHasSideEffects - The instruction has no side effects that are not
+ // captured by any operands of the instruction or other flags, and when
+ // *all* instances of the instruction of that opcode have no side effects.
+ // mayHaveSideEffects - Some instances of the instruction can have side
+ // effects. The virtual method "isReallySideEffectFree" is called to
+ // determine this. Load instructions are an example of where this is
+ // useful. In general, loads always have side effects. However, loads from
+ // constant pools don't. Individual back ends make this determination.
+ bit neverHasSideEffects = 0;
+ bit mayHaveSideEffects = 0;
InstrItinClass Itinerary = NoItinerary;// Execution steps used for scheduling.
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