diff --git a/llvm/lib/Transforms/Scalar/GVNSink.cpp b/llvm/lib/Transforms/Scalar/GVNSink.cpp
--- a/llvm/lib/Transforms/Scalar/GVNSink.cpp
+++ b/llvm/lib/Transforms/Scalar/GVNSink.cpp
@@ -46,6 +46,7 @@
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/Statistic.h"
 #include "llvm/ADT/StringExtras.h"
+#include "llvm/Analysis/AssumptionCache.h"
 #include "llvm/Analysis/GlobalsModRef.h"
 #include "llvm/IR/BasicBlock.h"
 #include "llvm/IR/CFG.h"
@@ -54,7 +55,9 @@
 #include "llvm/IR/InstrTypes.h"
 #include "llvm/IR/Instruction.h"
 #include "llvm/IR/Instructions.h"
+#include "llvm/IR/Intrinsics.h"
 #include "llvm/IR/PassManager.h"
+#include "llvm/IR/PatternMatch.h"
 #include "llvm/IR/Type.h"
 #include "llvm/IR/Use.h"
 #include "llvm/IR/Value.h"
@@ -562,7 +565,7 @@
 
 class GVNSink {
 public:
-  GVNSink() = default;
+  GVNSink(AssumptionCache *AC) : AC(AC) {}
 
   bool run(Function &F) {
     LLVM_DEBUG(dbgs() << "GVNSink: running on function @" << F.getName()
@@ -577,6 +580,7 @@
   }
 
 private:
+  AssumptionCache *AC;
   ValueTable VN;
 
   bool shouldAvoidSinkingInstruction(Instruction *I) {
@@ -868,6 +872,11 @@
     if (I != I0) {
       combineMetadataForCSE(I0, I, true);
       I0->andIRFlags(I);
+      // If assumptions are tracked we need to unregister any we will replace.
+      if (AC && isa<CallInst>(I) &&
+          match(cast<CallInst>(I),
+                llvm::PatternMatch::m_Intrinsic<Intrinsic::assume>()))
+        AC->unregisterAssumption(cast<CallInst>(I));
     }
 
   for (auto *I : Insts)
@@ -897,7 +906,10 @@
   bool runOnFunction(Function &F) override {
     if (skipFunction(F))
       return false;
-    GVNSink G;
+    AssumptionCache *AC = nullptr;
+    if (auto *ACT = getAnalysisIfAvailable<AssumptionCacheTracker>())
+      AC = &ACT->getAssumptionCache(F);
+    GVNSink G(AC);
     return G.run(F);
   }
 
@@ -909,7 +921,8 @@
 } // end anonymous namespace
 
 PreservedAnalyses GVNSinkPass::run(Function &F, FunctionAnalysisManager &AM) {
-  GVNSink G;
+  AssumptionCache *AC = AM.getCachedResult<AssumptionAnalysis>(F);
+  GVNSink G(AC);
   if (!G.run(F))
     return PreservedAnalyses::all();
 
diff --git a/llvm/test/Transforms/GVNSink/assumption.ll b/llvm/test/Transforms/GVNSink/assumption.ll
new file mode 100644
--- /dev/null
+++ b/llvm/test/Transforms/GVNSink/assumption.ll
@@ -0,0 +1,32 @@
+; RUN: opt < %s -S -passes="print<assumptions>,gvn-sink,loop-unroll" -unroll-count=3 | FileCheck %s
+;
+; This crashed because the cached assumption was replaced and the replacement
+; was then in the cache twice.
+;
+; PR49043
+
+@g = external global i32
+
+define void @main() {
+bb:
+  %i1.i = load volatile i32, i32* @g
+  %i32.i = icmp eq i32 %i1.i, 0
+  call void @llvm.assume(i1 %i32.i) #3
+  br label %bb4.i
+
+bb4.i:                                            ; preds = %bb4.i, %bb
+  %i.i = load volatile i32, i32* @g
+  %i3.i = icmp eq i32 %i.i, 0
+  call void @llvm.assume(i1 %i3.i) #3
+  br label %bb4.i
+
+func_1.exit:                                      ; No predecessors!
+  unreachable
+}
+
+declare void @llvm.assume(i1)
+
+; CHECK:  call void @llvm.assume(
+; CHECK:  call void @llvm.assume(
+; CHECK:  call void @llvm.assume(
+