From 4cd53531fdaf94786e19e9157744c6092b8de046 Mon Sep 17 00:00:00 2001
From: Hans Wennborg <hans@hanshq.net>
Date: Mon, 8 Sep 2014 20:24:10 +0000
Subject: [PATCH] Fast-ISel: Remove dead code after falling back from selecting
 call instructions (PR20863)

Previously, fast-isel would not clean up after failing to select a call
instruction, because it would have called flushLocalValueMap() which moves
the insertion point, making SavedInsertPt in selectInstruction() invalid.

Fixing this by making SavedInsertPt a member variable, and having
flushLocalValueMap() update it.

This removes some redundant code at -O0, and more importantly fixes PR20863.

Differential Revision: http://reviews.llvm.org/D5249

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@217401 91177308-0d34-0410-b5e6-96231b3b80d8
---
 include/llvm/CodeGen/FastISel.h       |  3 +++
 lib/CodeGen/SelectionDAG/FastISel.cpp | 25 ++++++++++---------------
 test/CodeGen/X86/fast-isel-x86.ll     | 18 ++++++++++++++++++
 3 files changed, 31 insertions(+), 15 deletions(-)

diff --git a/include/llvm/CodeGen/FastISel.h b/include/llvm/CodeGen/FastISel.h
index 561cb89ff4c..1232ec2aec9 100644
--- a/include/llvm/CodeGen/FastISel.h
+++ b/include/llvm/CodeGen/FastISel.h
@@ -539,6 +539,9 @@ private:
   /// across heavy instructions like calls.
   void flushLocalValueMap();
 
+  /// \brief Insertion point before trying to select the current instruction.
+  MachineBasicBlock::iterator SavedInsertPt;
+
   /// \brief Add a stackmap or patchpoint intrinsic call's live variable
   /// operands to a stackmap or patchpoint machine instruction.
   bool addStackMapLiveVars(SmallVectorImpl<MachineOperand> &Ops,
diff --git a/lib/CodeGen/SelectionDAG/FastISel.cpp b/lib/CodeGen/SelectionDAG/FastISel.cpp
index 0311140a299..40f387f3ba3 100644
--- a/lib/CodeGen/SelectionDAG/FastISel.cpp
+++ b/lib/CodeGen/SelectionDAG/FastISel.cpp
@@ -127,6 +127,7 @@ void FastISel::flushLocalValueMap() {
   LocalValueMap.clear();
   LastLocalValue = EmitStartPt;
   recomputeInsertPt();
+  SavedInsertPt = FuncInfo.InsertPt;
 }
 
 bool FastISel::hasTrivialKill(const Value *V) {
@@ -1296,7 +1297,7 @@ bool FastISel::selectInstruction(const Instruction *I) {
 
   DbgLoc = I->getDebugLoc();
 
-  MachineBasicBlock::iterator SavedInsertPt = FuncInfo.InsertPt;
+  SavedInsertPt = FuncInfo.InsertPt;
 
   if (const auto *Call = dyn_cast<CallInst>(I)) {
     const Function *F = Call->getCalledFunction();
@@ -1322,13 +1323,10 @@ bool FastISel::selectInstruction(const Instruction *I) {
       DbgLoc = DebugLoc();
       return true;
     }
-    // Remove dead code.  However, ignore call instructions since we've flushed
-    // the local value map and recomputed the insert point.
-    if (!isa<CallInst>(I)) {
-      recomputeInsertPt();
-      if (SavedInsertPt != FuncInfo.InsertPt)
-        removeDeadCode(FuncInfo.InsertPt, SavedInsertPt);
-    }
+    // Remove dead code.
+    recomputeInsertPt();
+    if (SavedInsertPt != FuncInfo.InsertPt)
+      removeDeadCode(FuncInfo.InsertPt, SavedInsertPt);
     SavedInsertPt = FuncInfo.InsertPt;
   }
   // Next, try calling the target to attempt to handle the instruction.
@@ -1337,13 +1335,10 @@ bool FastISel::selectInstruction(const Instruction *I) {
     DbgLoc = DebugLoc();
     return true;
   }
-  // Remove dead code.  However, ignore call instructions since we've flushed
-  // the local value map and recomputed the insert point.
-  if (!isa<CallInst>(I)) {
-    recomputeInsertPt();
-    if (SavedInsertPt != FuncInfo.InsertPt)
-      removeDeadCode(FuncInfo.InsertPt, SavedInsertPt);
-  }
+  // Remove dead code.
+  recomputeInsertPt();
+  if (SavedInsertPt != FuncInfo.InsertPt)
+    removeDeadCode(FuncInfo.InsertPt, SavedInsertPt);
 
   DbgLoc = DebugLoc();
   // Undo phi node updates, because they will be added again by SelectionDAG.
diff --git a/test/CodeGen/X86/fast-isel-x86.ll b/test/CodeGen/X86/fast-isel-x86.ll
index a212a7c6876..61e9b98f6e7 100644
--- a/test/CodeGen/X86/fast-isel-x86.ll
+++ b/test/CodeGen/X86/fast-isel-x86.ll
@@ -60,3 +60,21 @@ entry:
 ; CHECK: addl $28
 }
 declare fastcc void @test4fastccsret(%struct.a* sret)
+
+
+; Check that fast-isel cleans up when it fails to lower a call instruction.
+define void @test5() {
+entry:
+  %call = call i32 @test5dllimport(i32 42)
+  ret void
+; CHECK-LABEL: test5:
+; Local value area is still there:
+; CHECK: movl $42, {{%[a-z]+}}
+; Fast-ISel's arg push is not here:
+; CHECK-NOT: movl $42, (%esp)
+; SDag-ISel's arg push:
+; CHECK: movl %esp, [[REGISTER:%[a-z]+]]
+; CHECK: movl $42, ([[REGISTER]])
+; CHECK: movl __imp__test5dllimport
+}
+declare dllimport i32 @test5dllimport(i32)
-- 
2.34.1