[SimplifyCFG] Handle that first matched eq cond in if chain can be Extra condition.

Author: andjo403

llvm/lib/Transforms/Utils/SimplifyCFG.cpp

@@ -568,9 +568,20 @@ struct ConstantComparesGatherer {
   /// If the elements in Vals matches the comparisons
   bool IsEq = false;
 
+  // Used to check if the first matched CompValue shall be the Extra check.
+  bool IgnoreFirstMatch = false;
+  bool MultipleMatches = false;
+
   /// Construct and compute the result for the comparison instruction Cond
   ConstantComparesGatherer(Instruction *Cond, const DataLayout &DL) : DL(DL) {
     gather(Cond);
+    if (CompValue || !MultipleMatches)
+      return;
+    Extra = nullptr;
+    Vals.clear();
+    UsedICmps = 0;
+    IgnoreFirstMatch = true;
+    gather(Cond);
   }
 
   ConstantComparesGatherer(const ConstantComparesGatherer &) = delete;
@@ -581,8 +592,14 @@ struct ConstantComparesGatherer {
   /// Try to set the current value used for the comparison, it succeeds only if
   /// it wasn't set before or if the new value is the same as the old one
   bool setValueOnce(Value *NewVal) {
-    if (CompValue && CompValue != NewVal)
+    if (IgnoreFirstMatch && NewVal) {
+      IgnoreFirstMatch = false;
       return false;
+    }
+    if (CompValue && CompValue != NewVal) {
+      MultipleMatches = true;
+      return false;
+    }
     CompValue = NewVal;
     return (CompValue != nullptr);
   }

llvm/test/Transforms/SimplifyCFG/switch_create.ll

@@ -1129,16 +1129,18 @@ define void @extra_cond_is_eq_cmp(i8 %c, i32 %x)  {
 ; CHECK-LABEL: @extra_cond_is_eq_cmp(
 ; CHECK-NEXT:  entry:
 ; CHECK-NEXT:    [[CMP:%.*]] = icmp eq i32 [[X:%.*]], 32
-; CHECK-NEXT:    [[CMP4:%.*]] = icmp eq i8 [[C:%.*]], 97
-; CHECK-NEXT:    [[OR_COND:%.*]] = or i1 [[CMP]], [[CMP4]]
-; CHECK-NEXT:    [[CMP9:%.*]] = icmp eq i8 [[C]], 99
-; CHECK-NEXT:    [[TMP0:%.*]] = or i1 [[OR_COND]], [[CMP9]]
+; CHECK-NEXT:    [[TMP0:%.*]] = freeze i1 [[CMP]]
 ; CHECK-NEXT:    br i1 [[TMP0]], label [[IF_THEN:%.*]], label [[SWITCH_EARLY_TEST:%.*]]
+; CHECK:       switch.early.test:
+; CHECK-NEXT:    switch i8 [[C:%.*]], label [[COMMON_RET:%.*]] [
+; CHECK-NEXT:      i8 99, label [[IF_THEN]]
+; CHECK-NEXT:      i8 97, label [[IF_THEN]]
+; CHECK-NEXT:    ]
 ; CHECK:       common.ret:
 ; CHECK-NEXT:    ret void
 ; CHECK:       if.then:
 ; CHECK-NEXT:    tail call void @foo1()
-; CHECK-NEXT:    br label [[SWITCH_EARLY_TEST]]
+; CHECK-NEXT:    br label [[COMMON_RET]]
 ;
 entry:
   %cmp = icmp eq i32 %x, 32