[SimplifyCFG] Improve landing pad merge.

[trentxintong]

Summary

We can merge 2 landpad blocks without introducing a phi if the 2
blocks are originally feeding landingpad values to their successor.

[trentxintong]

I do not think this is correct. sorry for the noise.

lib/Transforms/Utils/SimplifyCFG.cpp

 ///
 /// TODO - This transformation could remove entries from a phi in the target
 /// block when the inputs in the phi are the same for the two blocks being
 /// merged.  In some cases, this could result in removal of the PHI entirely.
 static bool TryToMergeLandingPad(LandingPadInst *LPad, BranchInst *BI,
                                  BasicBlock *BB) {
   auto Succ = BB->getUniqueSuccessor();
   assert(Succ);
-  // If there's a phi in the successor block, we'd likely have to introduce
-  // a phi into the merged landing pad block.
-  if (isa<PHINode>(*Succ->begin()))
-    return false;
 
   for (BasicBlock *OtherPred : predecessors(Succ)) {
     if (BB == OtherPred)
       continue;
+
+    // If there's a phi in the successor block, we'd likely have to introduce
+    // a phi into the merged landing pad block unless both the incoming values
+    // are landingpad values.
+    if (PHINode *PN = dyn_cast<PHINode>(&*Succ->begin()))
+      if (!isa<LandingPadInst>(PN->getIncomingValueForBlock(BB)) ||
+          !isa<LandingPadInst>(PN->getIncomingValueForBlock(OtherPred)))
+         continue;
+
     BasicBlock::iterator I = OtherPred->begin();
     LandingPadInst *LPad2 = dyn_cast<LandingPadInst>(I);
     if (!LPad2 || !LPad2->isIdenticalTo(LPad))
       continue;
     for (++I; isa<DbgInfoIntrinsic>(I); ++I)
       ;
     BranchInst *BI2 = dyn_cast<BranchInst>(I);
     if (!BI2 || !BI2->isIdenticalTo(BI))

test/Transforms/SimplifyCFG/duplicate-landingpad.ll

 ; RUN: opt < %s -simplifycfg -S | FileCheck %s
 target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64-S128"
 
 declare i32 @__gxx_personality_v0(...)
 declare void @fn()
+declare void @handler(i8 *, i32)
+declare {i8*, i32} @bar({i8*, i32})
 
 
 ; CHECK-LABEL: @test1
 define void @test1() personality i32 (...)* @__gxx_personality_v0 {
 entry:
 ; CHECK-LABEL: entry:
 ; CHECK: to label %invoke2 unwind label %lpad2
   invoke void @fn()
lpad2:
   %exn2 = landingpad {i8*, i32}
           cleanup
   br label %shared_resume
 
 shared_resume:
   call void @fn()
   ret void
 }
+
+
+; CHECK-LABEL: @phiwithlandingpads
+define void @phiwithlandingpads() personality i32 (...)* @__gxx_personality_v0 {
+entry:
+; CHECK-LABEL: entry:
+; CHECK: to label %invoke2 unwind label %lpad2
+  invoke void @fn()
+    to label %invoke2 unwind label %lpad1
+
+invoke2:
+; CHECK-LABEL: invoke2:
+; CHECK: to label %invoke.cont unwind label %lpad2
+  invoke void @fn()
+    to label %invoke.cont unwind label %lpad2
+
+invoke.cont:
+  ret void
+
+lpad1:
+  %exn = landingpad {i8*, i32}
+         cleanup
+  br label %handler
+
+lpad2:
+; CHECK-LABEL: lpad2:
+; CHECK: landingpad { i8*, i32 }
+; CHECK-NEXT: cleanup
+; CHECK-NEXT: extractvalue
+; CHECK-NEXT: extractvalue
+; CHECK-NEXT: call void @handler
+; CHECK-NEXT: ret void
+  %exn2 = landingpad {i8*, i32}
+          cleanup
+  br label %handler
+
+handler:
+  %p = phi { i8*, i32 } [ %exn, %lpad1 ], [ %exn2, %lpad2 ]
+  %b1 = extractvalue { i8*, i32 } %p, 0
+  %b2 = extractvalue { i8*, i32 } %p, 1
+  call void @handler(i8* %b1, i32 %b2)
+  ret void
+}
+
+
+; CHECK-LABEL: @phiwithsomelandingpads
+define void @phiwithsomelandingpads() personality i32 (...)* @__gxx_personality_v0 {
+entry:
+; CHECK-LABEL: entry:
+; CHECK: to label %invoke2 unwind label %lpad1
+  invoke void @fn()
+    to label %invoke2 unwind label %lpad1
+
+invoke2:
+; CHECK-LABEL: invoke2:
+; CHECK: to label %invoke.cont unwind label %lpad2
+  invoke void @fn()
+    to label %invoke.cont unwind label %lpad2
+
+invoke.cont:
+  ret void
+
+lpad1:
+  %exn = landingpad {i8*, i32}
+         cleanup
+  %exn_s = call {i8*, i32} @bar({i8*, i32} %exn);
+  br label %handler
+
+lpad2:
+  %exn2 = landingpad {i8*, i32}
+          cleanup
+  br label %handler
+
+handler:
+  %p = phi { i8*, i32 } [ %exn_s, %lpad1 ], [ %exn2, %lpad2 ]
+  %b1 = extractvalue { i8*, i32 } %p, 0
+  %b2 = extractvalue { i8*, i32 } %p, 1
+  call void @handler(i8* %b1, i32 %b2)
+  ret void
+}