Index: llvm/test/tools/llvm-reduce/Inputs/test-crash-vars.py
===================================================================
--- /dev/null
+++ llvm/test/tools/llvm-reduce/Inputs/test-crash-vars.py
@@ -0,0 +1,9 @@
+import os
+import sys
+
+disable_crash_report = os.getenv("LLVM_DISABLE_CRASH_REPORT")
+disable_symbolization = os.getenv("LLVM_DISABLE_SYMBOLIZATION")
+
+# Test that this is an explicitly set true value. If we preserve the
+# debug environment a pre-set explicit 0 should work.
+sys.exit(disable_crash_report != "1" or disable_symbolization != "1")
Index: llvm/test/tools/llvm-reduce/disable-crash-reports.test
===================================================================
--- /dev/null
+++ llvm/test/tools/llvm-reduce/disable-crash-reports.test
@@ -0,0 +1,12 @@
+# RUN: llvm-reduce --delta-passes=global-variables --test %python --test-arg %p/Inputs/test-crash-vars.py %p/Inputs/test-output-format.ll 2>&1 | FileCheck -check-prefix=INTERESTING %s
+
+# RUN: LLVM_DISABLE_CRASH_REPORT=0 llvm-reduce --delta-passes=global-variables --test %python --test-arg %p/Inputs/test-crash-vars.py %p/Inputs/test-output-format.ll 2>&1 | FileCheck -check-prefix=INTERESTING %s
+
+# RUN: not llvm-reduce --preserve-debug-environment --delta-passes=global-variables --test %python --test-arg %p/Inputs/test-crash-vars.py %p/Inputs/test-output-format.ll 2>&1 | FileCheck -check-prefix=NOTINTERESTING %s
+
+# RUN: LLVM_DISABLE_CRASH_REPORT=0 not llvm-reduce --preserve-debug-environment --delta-passes=global-variables --test %python --test-arg %p/Inputs/test-crash-vars.py %p/Inputs/test-output-format.ll 2>&1 | FileCheck -check-prefix=NOTINTERESTING %s
+
+# RUN: LLVM_DISABLE_CRASH_REPORT=1 LLVM_DISABLE_SYMBOLIZATION=1 llvm-reduce --preserve-debug-environment --delta-passes=global-variables --test %python --test-arg %p/Inputs/test-crash-vars.py %p/Inputs/test-output-format.ll 2>&1 | FileCheck -check-prefix=INTERESTING %s
+
+INTERESTING: Done reducing! Reduced testcase:
+NOTINTERESTING: Input isn't interesting! Verify interesting-ness test
Index: llvm/tools/llvm-reduce/llvm-reduce.cpp
===================================================================
--- llvm/tools/llvm-reduce/llvm-reduce.cpp
+++ llvm/tools/llvm-reduce/llvm-reduce.cpp
@@ -18,14 +18,18 @@
 #include "ReducerWorkItem.h"
 #include "TestRunner.h"
 #include "llvm/CodeGen/CommandFlags.h"
-
 #include "llvm/Support/CommandLine.h"
 #include "llvm/Support/InitLLVM.h"
+#include "llvm/Support/Process.h"
 #include "llvm/Support/WithColor.h"
 #include "llvm/Support/raw_ostream.h"
 #include <system_error>
 #include <vector>
 
+#ifdef _WIN32
+#include <windows.h>
+#endif
+
 using namespace llvm;
 
 cl::OptionCategory LLVMReduceOptions("llvm-reduce options");
@@ -35,6 +39,12 @@
 static cl::opt<bool> Version("v", cl::desc("Alias for -version"), cl::Hidden,
                              cl::cat(LLVMReduceOptions));
 
+static cl::opt<bool> PreserveDebugEnvironment(
+    "preserve-debug-environment",
+    cl::desc("Don't disable features used for crash "
+             "debugging (crash reports, llvm-symbolizer and core dumps)"),
+    cl::cat(LLVMReduceOptions));
+
 static cl::opt<bool>
     PrintDeltaPasses("print-delta-passes",
                      cl::desc("Print list of delta passes, passable to "
@@ -93,6 +103,23 @@
 
 bool isReduced(ReducerWorkItem &M, const TestRunner &Test);
 
+/// Turn off crash debugging features
+///
+/// Crash is expected, so disable crash reports and symbolization to reduce
+/// output clutter and avoid potentially slow symbolization.
+static void disableEnvironmentDebugFeatures() {
+  sys::Process::PreventCoreFiles();
+
+  // TODO: Copied from not. Should have a wrapper around setenv.
+#ifdef _WIN32
+  SetEnvironmentVariableA("LLVM_DISABLE_CRASH_REPORT", "1");
+  SetEnvironmentVariableA("LLVM_DISABLE_SYMBOLIZATION", "1");
+#else
+  setenv("LLVM_DISABLE_CRASH_REPORT", "1", /*overwrite=*/1);
+  setenv("LLVM_DISABLE_SYMBOLIZATION", "1", /*overwrite=*/1);
+#endif
+}
+
 static std::pair<StringRef, bool> determineOutputType(bool IsMIR,
                                                       bool InputIsBitcode) {
   bool OutputBitcode = ForceOutputBitcode || InputIsBitcode;
@@ -146,6 +173,9 @@
     return 0;
   }
 
+  if (!PreserveDebugEnvironment)
+    disableEnvironmentDebugFeatures();
+
   LLVMContext Context;
   std::unique_ptr<TargetMachine> TM;