diff --git a/mlir/lib/Dialect/SCF/SCF.cpp b/mlir/lib/Dialect/SCF/SCF.cpp
--- a/mlir/lib/Dialect/SCF/SCF.cpp
+++ b/mlir/lib/Dialect/SCF/SCF.cpp
@@ -1519,51 +1519,98 @@
     if (!prevIf)
       return failure();
 
-    if (nextIf.getCondition() != prevIf.getCondition())
-      return failure();
+    // Determine the logical then/else blocks when prevIf's
+    // condition is used. Null means the block does not exist
+    // in that case (e.g. empty else). If neither of these
+    // are set, the two conditions cannot be compared.
+    Block *nextThen = nullptr;
+    Block *nextElse = nullptr;
+    if (nextIf.getCondition() == prevIf.getCondition()) {
+      nextThen = nextIf.thenBlock();
+      if (!nextIf.getElseRegion().empty())
+        nextElse = nextIf.elseBlock();
+    }
+    if (arith::XOrIOp notv =
+            nextIf.getCondition().getDefiningOp<arith::XOrIOp>()) {
+      if (notv.getLhs() == prevIf.getCondition() &&
+          matchPattern(notv.getRhs(), m_One())) {
+        nextElse = nextIf.thenBlock();
+        if (!nextIf.getElseRegion().empty())
+          nextThen = nextIf.elseBlock();
+      }
+    }
+    if (arith::XOrIOp notv =
+            prevIf.getCondition().getDefiningOp<arith::XOrIOp>()) {
+      if (notv.getLhs() == nextIf.getCondition() &&
+          matchPattern(notv.getRhs(), m_One())) {
+        nextElse = nextIf.thenBlock();
+        if (!nextIf.getElseRegion().empty())
+          nextThen = nextIf.elseBlock();
+      }
+    }
 
-    // Don't permit merging if a result of the first if is used
-    // within the second.
-    if (llvm::any_of(prevIf->getUsers(),
-                     [&](Operation *user) { return nextIf->isAncestor(user); }))
+    if (!nextThen && !nextElse)
       return failure();
 
+    SmallVector<Value> prevElseYielded;
+    if (!prevIf.getElseRegion().empty())
+      prevElseYielded = prevIf.elseYield().getOperands();
+    // Replace all uses of return values of op within nextIf with the
+    // corresponding yields
+    for (auto it : llvm::zip(prevIf.getResults(),
+                             prevIf.thenYield().getOperands(), prevElseYielded))
+      for (OpOperand &use :
+           llvm::make_early_inc_range(std::get<0>(it).getUses())) {
+        if (nextThen && nextThen->getParent()->isAncestor(
+                            use.getOwner()->getParentRegion())) {
+          rewriter.startRootUpdate(use.getOwner());
+          use.set(std::get<1>(it));
+          rewriter.finalizeRootUpdate(use.getOwner());
+        } else if (nextElse && nextElse->getParent()->isAncestor(
+                                   use.getOwner()->getParentRegion())) {
+          rewriter.startRootUpdate(use.getOwner());
+          use.set(std::get<2>(it));
+          rewriter.finalizeRootUpdate(use.getOwner());
+        }
+      }
+
     SmallVector<Type> mergedTypes(prevIf.getResultTypes());
     llvm::append_range(mergedTypes, nextIf.getResultTypes());
 
     IfOp combinedIf = rewriter.create<IfOp>(
-        nextIf.getLoc(), mergedTypes, nextIf.getCondition(), /*hasElse=*/false);
+        nextIf.getLoc(), mergedTypes, prevIf.getCondition(), /*hasElse=*/false);
     rewriter.eraseBlock(&combinedIf.getThenRegion().back());
 
-    YieldOp thenYield = prevIf.thenYield();
-    YieldOp thenYield2 = nextIf.thenYield();
-
-    combinedIf.getThenRegion().getBlocks().splice(
-        combinedIf.getThenRegion().getBlocks().begin(),
-        prevIf.getThenRegion().getBlocks());
-
-    rewriter.mergeBlocks(nextIf.thenBlock(), combinedIf.thenBlock());
-    rewriter.setInsertionPointToEnd(combinedIf.thenBlock());
-
-    SmallVector<Value> mergedYields(thenYield.getOperands());
-    llvm::append_range(mergedYields, thenYield2.getOperands());
-    rewriter.create<YieldOp>(thenYield2.getLoc(), mergedYields);
-    rewriter.eraseOp(thenYield);
-    rewriter.eraseOp(thenYield2);
+    rewriter.inlineRegionBefore(prevIf.getThenRegion(),
+                                combinedIf.getThenRegion(),
+                                combinedIf.getThenRegion().begin());
+
+    if (nextThen) {
+      YieldOp thenYield = combinedIf.thenYield();
+      YieldOp thenYield2 = cast<YieldOp>(nextThen->getTerminator());
+      rewriter.mergeBlocks(nextThen, combinedIf.thenBlock());
+      rewriter.setInsertionPointToEnd(combinedIf.thenBlock());
+
+      SmallVector<Value> mergedYields(thenYield.getOperands());
+      llvm::append_range(mergedYields, thenYield2.getOperands());
+      rewriter.create<YieldOp>(thenYield2.getLoc(), mergedYields);
+      rewriter.eraseOp(thenYield);
+      rewriter.eraseOp(thenYield2);
+    }
 
-    combinedIf.getElseRegion().getBlocks().splice(
-        combinedIf.getElseRegion().getBlocks().begin(),
-        prevIf.getElseRegion().getBlocks());
+    rewriter.inlineRegionBefore(prevIf.getElseRegion(),
+                                combinedIf.getElseRegion(),
+                                combinedIf.getElseRegion().begin());
 
-    if (!nextIf.getElseRegion().empty()) {
+    if (nextElse) {
       if (combinedIf.getElseRegion().empty()) {
-        combinedIf.getElseRegion().getBlocks().splice(
-            combinedIf.getElseRegion().getBlocks().begin(),
-            nextIf.getElseRegion().getBlocks());
+        rewriter.inlineRegionBefore(*nextElse->getParent(),
+                                    combinedIf.getElseRegion(),
+                                    combinedIf.getElseRegion().begin());
       } else {
         YieldOp elseYield = combinedIf.elseYield();
-        YieldOp elseYield2 = nextIf.elseYield();
-        rewriter.mergeBlocks(nextIf.elseBlock(), combinedIf.elseBlock());
+        YieldOp elseYield2 = cast<YieldOp>(nextElse->getTerminator());
+        rewriter.mergeBlocks(nextElse, combinedIf.elseBlock());
 
         rewriter.setInsertionPointToEnd(combinedIf.elseBlock());
 
diff --git a/mlir/test/Dialect/SCF/canonicalize.mlir b/mlir/test/Dialect/SCF/canonicalize.mlir
--- a/mlir/test/Dialect/SCF/canonicalize.mlir
+++ b/mlir/test/Dialect/SCF/canonicalize.mlir
@@ -1119,6 +1119,79 @@
 // CHECK-NEXT:       "test.secondCodeTrue"() : () -> ()
 // CHECK-NEXT:     }
 
+// CHECK-LABEL: @combineIfsUsed
+// CHECK-SAME: %[[arg0:.+]]: i1
+func @combineIfsUsed(%arg0 : i1, %arg2: i64) -> (i32, i32) {
+  %res = scf.if %arg0 -> i32 {
+    %v = "test.firstCodeTrue"() : () -> i32
+    scf.yield %v : i32
+  } else {
+    %v2 = "test.firstCodeFalse"() : () -> i32
+    scf.yield %v2 : i32
+  }
+  %res2 = scf.if %arg0 -> i32 {
+    %v = "test.secondCodeTrue"(%res) : (i32) -> i32
+    scf.yield %v : i32
+  } else {
+    %v2 = "test.secondCodeFalse"(%res) : (i32) -> i32
+    scf.yield %v2 : i32
+  }
+  return %res, %res2 : i32, i32
+}
+// CHECK-NEXT:     %[[res:.+]]:2 = scf.if %[[arg0]] -> (i32, i32) {
+// CHECK-NEXT:       %[[tval0:.+]] = "test.firstCodeTrue"() : () -> i32
+// CHECK-NEXT:       %[[tval:.+]] = "test.secondCodeTrue"(%[[tval0]]) : (i32) -> i32
+// CHECK-NEXT:       scf.yield %[[tval0]], %[[tval]] : i32, i32
+// CHECK-NEXT:     } else {
+// CHECK-NEXT:       %[[fval0:.+]] = "test.firstCodeFalse"() : () -> i32
+// CHECK-NEXT:       %[[fval:.+]] = "test.secondCodeFalse"(%[[fval0]]) : (i32) -> i32
+// CHECK-NEXT:       scf.yield %[[fval0]], %[[fval]] : i32, i32
+// CHECK-NEXT:     }
+// CHECK-NEXT:     return %[[res]]#0, %[[res]]#1 : i32, i32
+
+// CHECK-LABEL: @combineIfsNot
+// CHECK-SAME: %[[arg0:.+]]: i1
+func @combineIfsNot(%arg0 : i1, %arg2: i64) {
+  %true = arith.constant true
+  %not = arith.xori %arg0, %true : i1
+  scf.if %arg0 {
+    "test.firstCodeTrue"() : () -> ()
+    scf.yield
+  }
+  scf.if %not {
+    "test.secondCodeTrue"() : () -> ()
+    scf.yield
+  }
+  return
+}
+
+// CHECK-NEXT:     scf.if %[[arg0]] {
+// CHECK-NEXT:       "test.firstCodeTrue"() : () -> ()
+// CHECK-NEXT:     } else {
+// CHECK-NEXT:       "test.secondCodeTrue"() : () -> ()
+// CHECK-NEXT:     }
+
+// CHECK-LABEL: @combineIfsNot2
+// CHECK-SAME: %[[arg0:.+]]: i1
+func @combineIfsNot2(%arg0 : i1, %arg2: i64) {
+  %true = arith.constant true
+  %not = arith.xori %arg0, %true : i1
+  scf.if %not {
+    "test.firstCodeTrue"() : () -> ()
+    scf.yield
+  }
+  scf.if %arg0 {
+    "test.secondCodeTrue"() : () -> ()
+    scf.yield
+  }
+  return
+}
+
+// CHECK-NEXT:     scf.if %[[arg0]] {
+// CHECK-NEXT:       "test.secondCodeTrue"() : () -> ()
+// CHECK-NEXT:     } else {
+// CHECK-NEXT:       "test.firstCodeTrue"() : () -> ()
+// CHECK-NEXT:     }
 // -----
 
 // CHECK-LABEL: func @propagate_into_execute_region