Implement a signficant optimization for inline asm:

When choosing between constraints with multiple options,
like "ir", test to see if we can use the 'i' constraint and
go with that if possible.  This produces more optimal ASM in
all cases (sparing a register and an instruction to load it),
and fixes inline asm like this:

void test () {
  asm volatile (" %c0 %1 " : : "imr" (42), "imr"(14));
}

Previously we would dump "42" into a memory location (which
is ok for the 'm' constraint) which would cause a problem
because the 'c' modifier is not valid on memory operands.

Isn't it great how inline asm turns 'missed optimization'
into 'compile failed'??

Incidentally, this was the todo in 
PowerPC/2007-04-24-InlineAsm-I-Modifier.ll

Please do NOT pull this into Tak.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@50315 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 9 insertions, 4 deletions

diff --git a/include/llvm/Target/TargetLowering.h b/include/llvm/Target/TargetLowering.h
index 559f038..9b4c8af 100644
--- a/include/llvm/Target/TargetLowering.h
+++ b/include/llvm/Target/TargetLowering.h
@@ -109,7 +109,8 @@ public:
   /// srl/add/sra.
   bool isPow2DivCheap() const { return Pow2DivIsCheap; }
 
-  /// getSetCCResultType - Return the ValueType of the result of setcc operations.
+  /// getSetCCResultType - Return the ValueType of the result of setcc
+  /// operations.
   virtual MVT::ValueType getSetCCResultType(const SDOperand &) const;
 
   /// getSetCCResultContents - For targets without boolean registers, this flag
@@ -1080,8 +1081,12 @@ public:
 
   /// ComputeConstraintToUse - Determines the constraint code and constraint
   /// type to use for the specific AsmOperandInfo, setting
-  /// OpInfo.ConstraintCode and OpInfo.ConstraintType.
-  virtual void ComputeConstraintToUse(AsmOperandInfo &OpInfo) const;
+  /// OpInfo.ConstraintCode and OpInfo.ConstraintType.  If the actual operand
+  /// being passed in is available, it can be passed in as Op, otherwise an
+  /// empty SDOperand can be passed.
+  virtual void ComputeConstraintToUse(AsmOperandInfo &OpInfo,
+                                      SDOperand Op,
+                                      SelectionDAG *DAG = 0) const;
   
   /// getConstraintType - Given a constraint, return the type of constraint it
   /// is for this target.
@@ -1130,7 +1135,7 @@ public:
   // insert.  The specified MachineInstr is created but not inserted into any
   // basic blocks, and the scheduler passes ownership of it to this method.
   virtual MachineBasicBlock *EmitInstrWithCustomInserter(MachineInstr *MI,
-                                                         MachineBasicBlock *MBB);
+                                                        MachineBasicBlock *MBB);
 
   //===--------------------------------------------------------------------===//
   // Addressing mode description hooks (used by LSR etc).