diff --git a/llvm/lib/Analysis/InlineCost.cpp b/llvm/lib/Analysis/InlineCost.cpp
--- a/llvm/lib/Analysis/InlineCost.cpp
+++ b/llvm/lib/Analysis/InlineCost.cpp
@@ -2272,6 +2272,16 @@
   if (Call.isNoInline())
     return llvm::InlineCost::getNever("noinline call site attribute");
 
+  // Don't put nice code into functions that expose returnTwice.
+  // Reason is that (1) interaction of register spill and setjmp is buggy, and
+  // (2) for this reason, the code will probably be better optimized if outlined
+  // We still respect the AlwaysInline attribute, though, because technically we
+  // should not miscompile
+  if (!Callee->hasFnAttribute(Attribute::ReturnsTwice) &&
+      Caller->callsFunctionThatReturnsTwice()) {
+    return llvm::InlineCost::getNever("caller exposes ReturnsTwice");
+  }
+
   LLVM_DEBUG(llvm::dbgs() << "      Analyzing call of " << Callee->getName()
                           << "... (caller:" << Caller->getName() << ")\n");
 
diff --git a/llvm/lib/CodeGen/RegisterCoalescer.cpp b/llvm/lib/CodeGen/RegisterCoalescer.cpp
--- a/llvm/lib/CodeGen/RegisterCoalescer.cpp
+++ b/llvm/lib/CodeGen/RegisterCoalescer.cpp
@@ -3885,9 +3885,17 @@
   RegClassInfo.runOnMachineFunction(fn);
 
   // Join (coalesce) intervals if requested.
-  if (EnableJoining)
-    joinAllIntervals();
-
+  if (EnableJoining) {
+    // If there are calls to setjmp or sigsetjmp, don't coalesce registers
+    // cf https://bugs.llvm.org/show_bug.cgi?id=28431
+    if (MF->exposesReturnsTwice()) {
+      LLVM_DEBUG(
+          dbgs()
+          << "Skipping interval joining because of exposesReturnsTwice.\n");
+    } else {
+      joinAllIntervals();
+    }
+  }
   // After deleting a lot of copies, register classes may be less constrained.
   // Removing sub-register operands may allow GR32_ABCD -> GR32 and DPR_VFP2 ->
   // DPR inflation.
diff --git a/llvm/lib/CodeGen/StackColoring.cpp b/llvm/lib/CodeGen/StackColoring.cpp
--- a/llvm/lib/CodeGen/StackColoring.cpp
+++ b/llvm/lib/CodeGen/StackColoring.cpp
@@ -1174,6 +1174,14 @@
   if (!NumSlots)
     return false;
 
+  // If there are calls to setjmp or sigsetjmp, bail out.
+  // cf RegisterCoalescer and StackSlotColoring
+  // fixme: Is this too cautious? No known example that miscompiles due to this
+  if (Func.exposesReturnsTwice()) {
+    LLVM_DEBUG(dbgs() << "Skipping because of exposesReturnsTwice.\n");
+    return false;
+  }
+
   SmallVector<int, 8> SortedSlots;
   SortedSlots.reserve(NumSlots);
   Intervals.reserve(NumSlots);
diff --git a/llvm/lib/CodeGen/StackSlotColoring.cpp b/llvm/lib/CodeGen/StackSlotColoring.cpp
--- a/llvm/lib/CodeGen/StackSlotColoring.cpp
+++ b/llvm/lib/CodeGen/StackSlotColoring.cpp
@@ -505,9 +505,10 @@
   // coloring. The stack could be modified before the longjmp is executed,
   // resulting in the wrong value being used afterwards. (See
   // <rdar://problem/8007500>.)
-  if (MF.exposesReturnsTwice())
+  if (MF.exposesReturnsTwice()) {
+    LLVM_DEBUG(dbgs() << "Skipping because of exposesReturnsTwice.\n");
     return false;
-
+  }
   // Gather spill slot references
   ScanForSpillSlotRefs(MF);
   InitializeSlots();