[CodeGenPrepare] Don't sink a cast past its user

The sink cast machinery is supposed to sink casts as close to their user
as possible.  However, an EH pad is the first instruction in it's basic
block.  Don't sink if the user is an EH pad.

This fixes PR27536.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@267767 91177308-0d34-0410-b5e6-96231b3b80d8

lib/CodeGen/CodeGenPrepare.cpp

@@ -758,6 +758,11 @@ static bool SinkCast(CastInst *CI) {
     // Preincrement use iterator so we don't invalidate it.
     ++UI;
 
+    // The first insertion point of a block containing an EH pad is after the
+    // pad.  If the pad is the user, we cannot sink the cast past the pad.
+    if (User->isEHPad())
+      continue;
+
     // If the block selected to receive the cast is an EH pad that does not
     // allow non-PHI instructions before the terminator, we can't sink the
     // cast.

test/Transforms/CodeGenPrepare/X86/pr27536.ll

@@ -0,0 +1,32 @@
+; RUN: opt -S -codegenprepare < %s | FileCheck %s
+target datalayout = "e-m:w-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-pc-windows-msvc"
+
+@rtti = external global i8
+
+define void @test1() personality i32 (...)* @__CxxFrameHandler3 {
+entry:
+  %e = alloca i8
+  %tmpcast = bitcast i8* %e to i16*
+  invoke void @_CxxThrowException(i8* null, i8* null)
+          to label %catchret.dest unwind label %catch.dispatch
+
+catch.dispatch:                                   ; preds = %entry
+  %0 = catchswitch within none [label %catch] unwind to caller
+
+catch:                                            ; preds = %catch.dispatch
+  %1 = catchpad within %0 [i8* @rtti, i32 0, i16* %tmpcast]
+  catchret from %1 to label %catchret.dest
+
+catchret.dest:                                    ; preds = %catch
+  ret void
+}
+; CHECK-LABEL: define void @test1(
+; CHECK: %[[alloca:.*]] = alloca i8
+; CHECK-NEXT: %[[bc:.*]] = bitcast i8* %[[alloca]] to i16*
+
+; CHECK: catchpad within {{.*}} [i8* @rtti, i32 0, i16* %[[bc]]]
+
+declare void @_CxxThrowException(i8*, i8*)
+
+declare i32 @__CxxFrameHandler3(...)