[EVM][DAGCombine] Implement TLI hooks related to select

These hooks will reduce number of select instructions.

Signed-off-by: Vladimir Radosavljevic <[email protected]>

Author: vladimirradosavljevic

llvm/lib/Target/EVM/EVMISelLowering.h

@@ -115,6 +115,24 @@ class EVMTargetLowering final : public TargetLowering {
     return false;
   }
 
+  /// Returns true if we should normalize
+  /// select(N0&N1, X, Y) => select(N0, select(N1, X, Y), Y) and
+  /// select(N0|N1, X, Y) => select(N0, select(N1, X, Y, Y)) if it is likely
+  /// that it saves us from materializing N0 and N1 in an integer register.
+  /// For EVM, selects are expensive, so generating more selects is not
+  /// beneficial.
+  bool shouldNormalizeToSelectSequence(LLVMContext &Context,
+                                       EVT VT) const override {
+    return false;
+  }
+
+  /// Return true if a select of constants (select Cond, C1, C2) should be
+  /// transformed into simple math ops with the condition value. For example:
+  /// select Cond, C1, C1-1 --> add (zext Cond), C1-1
+  /// For EVM, selects are expensive, so reducing number of selects is
+  /// beneficial.
+  bool convertSelectOfConstantsToMath(EVT VT) const override { return true; }
+
 private:
   const EVMSubtarget *Subtarget;
 

llvm/test/CodeGen/EVM/dont-avoid-shift-transformations.ll

@@ -119,11 +119,10 @@ define i256 @test7(i256 %x) {
 ; CHECK-LABEL: test7:
 ; CHECK:       ; %bb.0: ; %entry
 ; CHECK-NEXT:    JUMPDEST
-; CHECK-NEXT:    PUSH1 0x2
-; CHECK-NEXT:    SWAP1
-; CHECK-NEXT:    PUSH1 0xFE
+; CHECK-NEXT:    PUSH1 0xFF
 ; CHECK-NEXT:    SHR
-; CHECK-NEXT:    AND
+; CHECK-NEXT:    PUSH1 0x1
+; CHECK-NEXT:    SHL
 ; CHECK-NEXT:    SWAP1
 ; CHECK-NEXT:    JUMP
 entry: