Index: lib/Target/WebAssembly/WebAssemblyFixFunctionBitcasts.cpp
===================================================================
--- lib/Target/WebAssembly/WebAssemblyFixFunctionBitcasts.cpp
+++ lib/Target/WebAssembly/WebAssemblyFixFunctionBitcasts.cpp
@@ -23,6 +23,7 @@
 //===----------------------------------------------------------------------===//
 
 #include "WebAssembly.h"
+#include "llvm/ADT/Triple.h"
 #include "llvm/IR/CallSite.h"
 #include "llvm/IR/Constants.h"
 #include "llvm/IR/Instructions.h"
@@ -226,6 +227,23 @@
   return Wrapper;
 }
 
+// Test whether a main function with type FuncTy should be rewritten to have
+// type MainTy.
+bool ShouldFixMainFunction(FunctionType *FuncTy,
+                           FunctionType *MainTy,
+                           Module &M) {
+  if (Triple(M.getTargetTriple()).isOSWASI()) {
+    // For WASI, only fix the main function if it's the standard zero-arg form.
+    // That way, the standard cases will work as expected, and users will see
+    // signature mismatches from the linker for non-standard cases.
+    return FuncTy->getReturnType() == MainTy->getReturnType() &&
+           FuncTy->getNumParams() == 0 &&
+           !FuncTy->isVarArg();
+  }
+
+  return FuncTy != MainTy;
+}
+
 bool FixFunctionBitcasts::runOnModule(Module &M) {
   LLVM_DEBUG(dbgs() << "********** Fix Function Bitcasts **********\n");
 
@@ -234,6 +252,12 @@
   SmallVector<std::pair<Use *, Function *>, 0> Uses;
   SmallPtrSet<Constant *, 2> ConstantBCs;
 
+  // In general, main-function fixup is disabled because it breaks some tests
+  // involving three-argument (with envp) main functions. On WASI,
+  // three-argument main functions are not supported.
+  bool FixMainFunctions = Triple(M.getTargetTriple()).isOSWASI() ||
+                          !TemporaryWorkarounds;
+
   // Collect all the places that need wrappers.
   for (Function &F : M) {
     FindUses(&F, F, Uses, ConstantBCs);
@@ -242,14 +266,14 @@
     // "int main(int argc, char *argv[])", create an artificial call with it
     // bitcasted to that type so that we generate a wrapper for it, so that
     // the C runtime can call it.
-    if (!TemporaryWorkarounds && !F.isDeclaration() && F.getName() == "main") {
+    if (FixMainFunctions && !F.isDeclaration() && F.getName() == "main") {
       Main = &F;
       LLVMContext &C = M.getContext();
       Type *MainArgTys[] = {Type::getInt32Ty(C),
                             PointerType::get(Type::getInt8PtrTy(C), 0)};
       FunctionType *MainTy = FunctionType::get(Type::getInt32Ty(C), MainArgTys,
                                                /*isVarArg=*/false);
-      if (F.getFunctionType() != MainTy) {
+      if (ShouldFixMainFunction(F.getFunctionType(), MainTy, M)) {
         LLVM_DEBUG(dbgs() << "Found `main` function with incorrect type: "
                           << *F.getFunctionType() << "\n");
         Value *Args[] = {UndefValue::get(MainArgTys[0]),
Index: test/CodeGen/WebAssembly/wasi-main-no-args.ll
===================================================================
--- test/CodeGen/WebAssembly/wasi-main-no-args.ll
+++ test/CodeGen/WebAssembly/wasi-main-no-args.ll
@@ -1,16 +1,17 @@
-; RUN: llc < %s -asm-verbose=false -wasm-temporary-workarounds=false | FileCheck %s
+; RUN: llc < %s -asm-verbose=false | FileCheck %s
 
 ; Test main functions with alternate signatures.
 
 target datalayout = "e-m:e-p:32:32-i64:64-n32:64-S128"
-target triple = "wasm32-unknown-unknown"
+target triple = "wasm32-unknown-wasi"
 
-define void @main() {
-  ret void
+define i32 @main() {
+  ret i32 0
 }
 
 ; CHECK-LABEL: .L__original_main:
-; CHECK-NEXT: .functype .L__original_main () -> ()
+; CHECK-NEXT: .functype .L__original_main () -> (i32)
+; CHECK-NEXT: i32.const 0
 ; CHECK-NEXT: end_function
 
 ; CHECK-LABEL: main:
Index: test/CodeGen/WebAssembly/wasi-main-three-args.ll
===================================================================
--- test/CodeGen/WebAssembly/wasi-main-three-args.ll
+++ test/CodeGen/WebAssembly/wasi-main-three-args.ll
@@ -1,15 +1,16 @@
-; RUN: llc < %s -asm-verbose=false -wasm-temporary-workarounds=false | FileCheck %s
+; RUN: llc < %s -asm-verbose=false | FileCheck %s
 
-; Test that main function with expected signature is not wrapped
+; Test that main function with a non-standard third argument is
+; not wrapped on WASI.
 
 target datalayout = "e-m:e-p:32:32-i64:64-n32:64-S128"
-target triple = "wasm32-unknown-unknown"
+target triple = "wasm32-unknown-wasi"
 
-define i32 @main(i32 %a, i8** %b) {
+define i32 @main(i32 %a, i8** %b, i8** %c) {
   ret i32 0
 }
 
 ; CHECK-LABEL: main:
-; CHECK-NEXT: .functype main (i32, i32) -> (i32)
+; CHECK-NEXT: .functype main (i32, i32, i32) -> (i32)
 
 ; CHECK-NOT: __original_main:
Index: test/CodeGen/WebAssembly/wasi-main-with-args.ll
===================================================================
--- test/CodeGen/WebAssembly/wasi-main-with-args.ll
+++ test/CodeGen/WebAssembly/wasi-main-with-args.ll
@@ -1,9 +1,9 @@
-; RUN: llc < %s -asm-verbose=false -wasm-temporary-workarounds=false | FileCheck %s
+; RUN: llc < %s -asm-verbose=false | FileCheck %s
 
 ; Test that main function with expected signature is not wrapped
 
 target datalayout = "e-m:e-p:32:32-i64:64-n32:64-S128"
-target triple = "wasm32-unknown-unknown"
+target triple = "wasm32-unknown-wasi"
 
 define i32 @main(i32 %a, i8** %b) {
   ret i32 0