!fixup don't perform transform with large clusters.

Author: fhahn

llvm/lib/CodeGen/SwitchLoweringUtils.cpp

@@ -363,6 +363,12 @@ void SwitchCG::SwitchLowering::findBitTestClusters(CaseClusterVector &Clusters,
   }
   Clusters.resize(DstIndex);
 
+  // Don't try to fold clusters checking for zero and a power-of-2 constant, if
+  // larger ranges may be lowered as balanced binary trees later on, which won't
+  // work correctly after applying the transform below.
+  if (Clusters.size() > 4)
+    return;
+
   // Check if the clusters contain one checking for 0 and another one checking
   // for a power-of-2 constant with matching destinations. Those clusters can be
   // combined to a single one with CC_And.

llvm/test/CodeGen/AArch64/switch-cases-to-branch-and.ll

@@ -878,56 +878,63 @@ pow2.dst:
 define void @switch_large_enough_for_clustering(i32 %x, ptr %dst) {
 ; CHECK-LABEL: switch_large_enough_for_clustering:
 ; CHECK:       ; %bb.0: ; %entry
-; CHECK-NEXT:    cmp w0, #3
-; CHECK-NEXT:    b.gt LBB12_4
+; CHECK-NEXT:    cmp w0, #1
+; CHECK-NEXT:    b.le LBB12_5
 ; CHECK-NEXT:  ; %bb.1: ; %entry
-; CHECK-NEXT:    tst w0, #0xfffffffd
-; CHECK-NEXT:    b.ne LBB12_7
-; CHECK-NEXT:  ; %bb.2: ; %succ.1
-; CHECK-NEXT:    strb wzr, [x1]
-; CHECK-NEXT:  LBB12_3: ; %exit
-; CHECK-NEXT:    ret
-; CHECK-NEXT:  LBB12_4: ; %entry
+; CHECK-NEXT:    cmp w0, #7
+; CHECK-NEXT:    b.eq LBB12_9
+; CHECK-NEXT:  ; %bb.2: ; %entry
 ; CHECK-NEXT:    cmp w0, #4
+; CHECK-NEXT:    b.eq LBB12_7
+; CHECK-NEXT:  ; %bb.3: ; %entry
+; CHECK-NEXT:    cmp w0, #2
 ; CHECK-NEXT:    b.eq LBB12_8
-; CHECK-NEXT:  ; %bb.5: ; %entry
-; CHECK-NEXT:    cmp w0, #7
-; CHECK-NEXT:    b.ne LBB12_3
-; CHECK-NEXT:  ; %bb.6: ; %succ.3
-; CHECK-NEXT:    strh wzr, [x1]
+; CHECK-NEXT:  LBB12_4: ; %exit
 ; CHECK-NEXT:    ret
-; CHECK-NEXT:  LBB12_7: ; %entry
+; CHECK-NEXT:  LBB12_5: ; %entry
+; CHECK-NEXT:    cbz w0, LBB12_8
+; CHECK-NEXT:  ; %bb.6: ; %entry
 ; CHECK-NEXT:    cmp w0, #1
-; CHECK-NEXT:    b.ne LBB12_3
-; CHECK-NEXT:  LBB12_8: ; %succ.2
+; CHECK-NEXT:    b.ne LBB12_4
+; CHECK-NEXT:  LBB12_7: ; %succ.2
 ; CHECK-NEXT:    str wzr, [x1]
 ; CHECK-NEXT:    ret
+; CHECK-NEXT:  LBB12_8: ; %succ.1
+; CHECK-NEXT:    strb wzr, [x1]
+; CHECK-NEXT:    ret
+; CHECK-NEXT:  LBB12_9: ; %succ.3
+; CHECK-NEXT:    strh wzr, [x1]
+; CHECK-NEXT:    ret
 ;
 ; GISEL-LABEL: switch_large_enough_for_clustering:
 ; GISEL:       ; %bb.0: ; %entry
-; GISEL-NEXT:    cmp w0, #4
-; GISEL-NEXT:    b.ge LBB12_4
+; GISEL-NEXT:    cmp w0, #2
+; GISEL-NEXT:    b.lt LBB12_5
 ; GISEL-NEXT:  ; %bb.1: ; %entry
-; GISEL-NEXT:    cmn w0, #3
-; GISEL-NEXT:    b.ne LBB12_7
-; GISEL-NEXT:  ; %bb.2: ; %succ.1
-; GISEL-NEXT:    strb wzr, [x1]
-; GISEL-NEXT:  LBB12_3: ; %exit
-; GISEL-NEXT:    ret
-; GISEL-NEXT:  LBB12_4: ; %entry
-; GISEL-NEXT:    b.eq LBB12_8
-; GISEL-NEXT:  ; %bb.5: ; %entry
 ; GISEL-NEXT:    cmp w0, #7
-; GISEL-NEXT:    b.ne LBB12_3
-; GISEL-NEXT:  ; %bb.6: ; %succ.3
-; GISEL-NEXT:    strh wzr, [x1]
+; GISEL-NEXT:    b.eq LBB12_9
+; GISEL-NEXT:  ; %bb.2: ; %entry
+; GISEL-NEXT:    cmp w0, #4
+; GISEL-NEXT:    b.eq LBB12_7
+; GISEL-NEXT:  ; %bb.3: ; %entry
+; GISEL-NEXT:    cmp w0, #2
+; GISEL-NEXT:    b.eq LBB12_8
+; GISEL-NEXT:  LBB12_4: ; %exit
 ; GISEL-NEXT:    ret
-; GISEL-NEXT:  LBB12_7: ; %entry
+; GISEL-NEXT:  LBB12_5: ; %entry
+; GISEL-NEXT:    cbz w0, LBB12_8
+; GISEL-NEXT:  ; %bb.6: ; %entry
 ; GISEL-NEXT:    cmp w0, #1
-; GISEL-NEXT:    b.ne LBB12_3
-; GISEL-NEXT:  LBB12_8: ; %succ.2
+; GISEL-NEXT:    b.ne LBB12_4
+; GISEL-NEXT:  LBB12_7: ; %succ.2
 ; GISEL-NEXT:    str wzr, [x1]
 ; GISEL-NEXT:    ret
+; GISEL-NEXT:  LBB12_8: ; %succ.1
+; GISEL-NEXT:    strb wzr, [x1]
+; GISEL-NEXT:    ret
+; GISEL-NEXT:  LBB12_9: ; %succ.3
+; GISEL-NEXT:    strh wzr, [x1]
+; GISEL-NEXT:    ret
 entry:
   switch i32 %x, label %exit [
     i32 0, label %succ.1