[PATCH] D103057: [SystemZ] Return true from preferZeroCompareBranch()

[Jonas Paulsson via Phabricator via llvm-commits]

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Doing this seems to eliminate compares overall on benchmarks:

  cijlh          :                78588                77953     -635
  ahik           :                72595                71970     -625
  jlh            :               165486               166049     +563
  ahi            :                89115                89660     +545
  je             :               337157               337319     +162
  ...


https://reviews.llvm.org/D103057

Files:
  llvm/lib/Target/SystemZ/SystemZISelLowering.h
  llvm/test/CodeGen/SystemZ/codegenprepare-form-OF-ops.ll


Index: llvm/test/CodeGen/SystemZ/codegenprepare-form-OF-ops.ll
===================================================================
--- llvm/test/CodeGen/SystemZ/codegenprepare-form-OF-ops.ll
+++ llvm/test/CodeGen/SystemZ/codegenprepare-form-OF-ops.ll
@@ -52,3 +52,41 @@
   %tmp12 = select i1 %tmp10, i64 %tmp11, i64 %arg
   ret i64 %tmp12
 }
+
+define i32 @optbranch_32(i32 %Arg) {
+; CHECK-LABEL: optbranch_32:
+; CHECK:        alhsik	%r2, %r2, 1
+; CHECK-NEXT:   bler	%r14
+; CHECK-NEXT:   .LBB4_1:
+; CHECK-NEXT: 	lhi	%r2, -1
+; CHECK-NEXT: 	br	%r14
+bb:
+  %i1 = icmp eq i32 %Arg, -1
+  br i1 %i1, label %bb2, label %bb3
+
+bb2:
+  ret i32 -1
+
+bb3:
+  %i4 = add nuw i32 %Arg, 1
+  ret i32 %i4
+}
+
+define i64 @optbranch_64(i64 %Arg) {
+; CHECK-LABEL: optbranch_64:
+; CHECK:        alghsik	%r2, %r2, 1
+; CHECK-NEXT:   bler	%r14
+; CHECK-NEXT:   .LBB5_1:
+; CHECK-NEXT: 	lghi	%r2, -1
+; CHECK-NEXT: 	br	%r14
+bb:
+  %i1 = icmp eq i64 %Arg, -1
+  br i1 %i1, label %bb2, label %bb3
+
+bb2:
+  ret i64 -1
+
+bb3:
+  %i4 = add nuw i64 %Arg, 1
+  ret i64 %i4
+}
Index: llvm/lib/Target/SystemZ/SystemZISelLowering.h
===================================================================
--- llvm/lib/Target/SystemZ/SystemZISelLowering.h
+++ llvm/lib/Target/SystemZ/SystemZISelLowering.h
@@ -423,6 +423,7 @@
     return TargetLoweringBase::getPreferredVectorAction(VT);
   }
   bool isCheapToSpeculateCtlz() const override { return true; }
+  bool preferZeroCompareBranch() const override { return true; }
   EVT getSetCCResultType(const DataLayout &DL, LLVMContext &,
                          EVT) const override;
   bool isFMAFasterThanFMulAndFAdd(const MachineFunction &MF,


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