[SimplifyCFG] Handle that first matched eq cond in if chain can be Extra condition. (#154007)

Proof: https://alive2.llvm.org/ce/z/TozSD6

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;
@@ -581,10 +592,16 @@ 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) {
+      IgnoreFirstMatch = false;
       return false;
+    }
+    if (CompValue && CompValue != NewVal) {
+      MultipleMatches = true;
+      return false;
+    }
     CompValue = NewVal;
-    return (CompValue != nullptr);
+    return true;
   }
 
   /// Try to match Instruction "I" as a comparison against a constant and

llvm/test/Transforms/SimplifyCFG/switch_create.ll

@@ -1125,3 +1125,70 @@ F:
   ret void
 }
 
+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:    [[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 [[COMMON_RET]]
+;
+entry:
+  %cmp = icmp eq i32 %x, 32
+  %cmp4 = icmp eq i8 %c, 97
+  %or.cond = or i1 %cmp, %cmp4
+  %cmp9 = icmp eq i8 %c, 99
+  %or.cond11 = or i1 %or.cond, %cmp9
+  br i1 %or.cond11, label %if.then, label %if.end
+
+if.then:
+  tail call void @foo1()
+  ret void
+
+if.end:
+  ret void
+
+}
+
+define void @extra_cond_is_eq_cmp_c(i8 %c, i32 %x)  {
+; CHECK-LABEL: @extra_cond_is_eq_cmp_c(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[CMP:%.*]] = icmp eq i32 [[X:%.*]], 32
+; 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 [[COMMON_RET]]
+;
+entry:
+  %cmp = icmp eq i32 %x, 32
+  %cmp4 = icmp eq i8 %c, 97
+  %or.cond = or i1 %cmp4, %cmp
+  %cmp9 = icmp eq i8 %c, 99
+  %or.cond11 = or i1 %or.cond, %cmp9
+  br i1 %or.cond11, label %if.then, label %if.end
+
+if.then:
+  tail call void @foo1()
+  ret void
+
+if.end:
+  ret void
+
+}