[WinEH] Replace more lpad value uses with undef

We were asserting on code like this:
  extern "C" unsigned long _exception_code();
  void might_crash(unsigned long);
  void foo() {
    __try {
      might_crash(0);
    } __except(1) {
      might_crash(_exception_code());
    }
  }

Gtest and many other libraries get the exception code from the __except
block. What's supposed to happen here is that EAX is live into the
__except block, and it contains the exception code. Eventually we'll
represent that as a use of the landingpad ehptr value, but for now we
can replace it with undef.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@235649 91177308-0d34-0410-b5e6-96231b3b80d8

lib/CodeGen/WinEHPrepare.cpp

@@ -696,10 +696,6 @@ bool WinEHPrepare::prepareExceptionHandlers(
       Invoke->setUnwindDest(NewLPadBB);
     }
 
-    // If anyone is still using the old landingpad value, just give them undef
-    // instead. The eh pointer and selector values are not real.
-    LPad->replaceAllUsesWith(UndefValue::get(LPad->getType()));
-
     // Replace the mapping of any nested landing pad that previously mapped
     // to this landing pad with a referenced to the cloned version.
     for (auto &LPadPair : NestedLPtoOriginalLP) {
@@ -709,11 +705,26 @@ bool WinEHPrepare::prepareExceptionHandlers(
       }
     }
 
-    // Replace uses of the old lpad in phis with this block and delete the old
+    // Replace all extracted values with undef and ultimately replace the
-    // block.
+    // landingpad with undef.
-    LPadBB->replaceSuccessorsPhiUsesWith(NewLPadBB);
+    // FIXME: This doesn't handle SEH GetExceptionCode(). For now, we just give
-    LPadBB->getTerminator()->eraseFromParent();
+    // out undef until we figure out the codegen support.
-    new UnreachableInst(LPadBB->getContext(), LPadBB);
+    SmallVector<Instruction *, 4> Extracts;
+    for (User *U : LPad->users()) {
+      auto *E = dyn_cast<ExtractValueInst>(U);
+      if (!E)
+        continue;
+      assert(E->getNumIndices() == 1 &&
+             "Unexpected operation: extracting both landing pad values");
+      unsigned Idx = E->getIndices()[0];
+      assert(Idx == 0 || Idx == 1);
+      Extracts.push_back(E);
+    }
+    for (Instruction *E : Extracts) {
+      E->replaceAllUsesWith(UndefValue::get(E->getType()));
+      E->eraseFromParent();
+    }
+    LPad->replaceAllUsesWith(UndefValue::get(LPad->getType()));
 
     // Add a call to describe the actions for this landing pad.
     std::vector<Value *> ActionArgs;

test/CodeGen/WinEH/seh-resume-phi.ll

@@ -0,0 +1,67 @@
+; RUN: opt -S -winehprepare -sehprepare < %s | FileCheck %s
+
+target datalayout = "e-m:w-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-pc-windows-msvc"
+
+declare void @might_crash(i8* %ehptr)
+declare i32 @filt()
+declare void @cleanup()
+declare i32 @__C_specific_handler(...)
+declare i32 @llvm.eh.typeid.for(i8*)
+
+define void @resume_phi() {
+entry:
+  invoke void @might_crash(i8* null)
+          to label %return unwind label %lpad1
+
+lpad1:
+  %ehvals1 = landingpad { i8*, i32 } personality i32 (...)* @__C_specific_handler
+          catch i32 ()* @filt
+  %ehptr1 = extractvalue { i8*, i32 } %ehvals1, 0
+  %ehsel1 = extractvalue { i8*, i32 } %ehvals1, 1
+  %filt_sel = tail call i32 @llvm.eh.typeid.for(i8* bitcast (i32 ()* @filt to i8*))
+  %matches = icmp eq i32 %ehsel1, %filt_sel
+  br i1 %matches, label %__except, label %eh.resume
+
+__except:
+  invoke void @might_crash(i8* %ehptr1)
+          to label %return unwind label %lpad2
+
+lpad2:
+  %ehvals2 = landingpad { i8*, i32 } personality i32 (...)* @__C_specific_handler
+          cleanup
+  %ehptr2 = extractvalue { i8*, i32 } %ehvals2, 0
+  %ehsel2 = extractvalue { i8*, i32 } %ehvals2, 1
+  call void @cleanup()
+  br label %eh.resume
+
+return:
+  ret void
+
+eh.resume:
+  %ehptr.phi = phi i8* [ %ehptr1, %lpad1 ], [ %ehptr2, %lpad2 ]
+  %ehsel.phi = phi i32 [ %ehsel1, %lpad1 ], [ %ehsel2, %lpad2 ]
+  %ehval.phi1 = insertvalue { i8*, i32 } undef, i8* %ehptr.phi, 0
+  %ehval.phi2 = insertvalue { i8*, i32 } %ehval.phi1, i32 %ehsel.phi, 1
+  resume { i8*, i32 } %ehval.phi2
+}
+
+; CHECK-LABEL: define void @resume_phi()
+; CHECK: invoke void @might_crash(i8* null)
+; CHECK: landingpad { i8*, i32 }
+; CHECK-NEXT: catch i32 ()* @filt
+; CHECK-NEXT: call i8* (...) @llvm.eh.actions(
+; CHECK-SAME: i32 1, i8* bitcast (i32 ()* @filt to i8*), i32 -1, i8* blockaddress(@resume_phi, %__except))
+; CHECK-NEXT: indirectbr {{.*}} [label %__except]
+;
+; CHECK: __except:
+;      FIXME: This should not be undef, it should be the new landingpad value, which
+;      should ultimately lower down to eax.
+; CHECK: invoke void @might_crash(i8* undef)
+; CHECK: landingpad { i8*, i32 }
+; CHECK-NEXT: cleanup
+; CHECK-NEXT: call i8* (...) @llvm.eh.actions(i32 0, void (i8*, i8*)* @resume_phi.cleanup)
+; CHECK-NEXT: indirectbr {{.*}} []
+
+; CHECK-LABEL: define internal void @resume_phi.cleanup(i8*, i8*)
+; CHECK: call void @cleanup()