[TargetLowering][DAGCombine][MSP430] Shift Amount Threshold in DAGCombine (4)

Summary:
Replaces
```
unsigned getShiftAmountThreshold(EVT VT)
```
by

```
bool shouldAvoidTransformToShift(EVT VT, unsigned amount)
```
thus giving more flexibility for targets to decide whether particular shift amounts must be considered expensive or not.

Updates the MSP430 target with a custom implementation.

This continues  D69116, D69120, D69326 and updates them, so all of them must be committed before this.

Existing tests apply, a few more have been added.

Reviewers: asl, spatel

Reviewed By: spatel

Subscribers: hiraditya, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D70042

2 files changed, 5 insertions, 4 deletions

diff --git a/llvm/lib/Target/MSP430/MSP430ISelLowering.cpp b/llvm/lib/Target/MSP430/MSP430ISelLowering.cpp
index b6a658f30a8..37e6ea24d08 100644
--- a/llvm/lib/Target/MSP430/MSP430ISelLowering.cpp
+++ b/llvm/lib/Target/MSP430/MSP430ISelLowering.cpp
@@ -358,9 +358,10 @@ SDValue MSP430TargetLowering::LowerOperation(SDValue Op,
   }
 }
 
-// Set transforms into shift amounts above 2 as not profitable
-unsigned MSP430TargetLowering::getShiftAmountThreshold(EVT VT) const {
-  return 2;
+// Define non profitable transforms into shifts
+bool MSP430TargetLowering::shouldAvoidTransformToShift(EVT VT,
+                                                       unsigned Amount) const {
+  return !(Amount == 8 || Amount == 9 || Amount<=2);
 }
 
 // Implemented to verify test case assertions in
diff --git a/llvm/lib/Target/MSP430/MSP430ISelLowering.h b/llvm/lib/Target/MSP430/MSP430ISelLowering.h
index 64ddbbdf6c8..650f9a70406 100644
--- a/llvm/lib/Target/MSP430/MSP430ISelLowering.h
+++ b/llvm/lib/Target/MSP430/MSP430ISelLowering.h
@@ -125,7 +125,7 @@ namespace llvm {
     bool isZExtFree(SDValue Val, EVT VT2) const override;
 
     bool isLegalICmpImmediate(int64_t) const override;
-    unsigned getShiftAmountThreshold(EVT VT) const override;
+    bool shouldAvoidTransformToShift(EVT VT, unsigned Amount) const override;
 
     MachineBasicBlock *
     EmitInstrWithCustomInserter(MachineInstr &MI,