From d0641826121d61cbf688dc8cd4bd368939292689 Mon Sep 17 00:00:00 2001
From: Roman Lebedev <lebedev.ri@gmail.com>
Date: Thu, 24 Jun 2021 21:25:06 +0300
Subject: [PATCH] [SimplifyCFG] Tail-merging all blocks with `resume`
 terminator

Similar to what we already do for `ret` terminators.
As noted by @rnk, clang seems to already generate a single `ret`/`resume`,
so this isn't likely to cause widespread changes.

Reviewed By: rnk

Differential Revision: https://reviews.llvm.org/D104849
---
 llvm/lib/Transforms/Scalar/SimplifyCFGPass.cpp    |  9 +++++++--
 .../Transforms/SimplifyCFG/tail-merge-resume.ll   | 15 ++++++++-------
 2 files changed, 15 insertions(+), 9 deletions(-)

diff --git a/llvm/lib/Transforms/Scalar/SimplifyCFGPass.cpp b/llvm/lib/Transforms/Scalar/SimplifyCFGPass.cpp
index dc21b3c72689..09d59b0e884a 100644
--- a/llvm/lib/Transforms/Scalar/SimplifyCFGPass.cpp
+++ b/llvm/lib/Transforms/Scalar/SimplifyCFGPass.cpp
@@ -94,10 +94,15 @@ static bool tailMergeBlocksWithSimilarFunctionTerminators(Function &F,
 
     auto *Term = BB.getTerminator();
 
-    // Fow now only support `ret` function terminators.
+    // Fow now only support `ret`/`resume` function terminators.
     // FIXME: lift this restriction.
-    if (Term->getOpcode() != Instruction::Ret)
+    switch (Term->getOpcode()) {
+    case Instruction::Ret:
+    case Instruction::Resume:
+      break;
+    default:
       continue;
+    }
 
     // We can't tail-merge block that contains a musttail call.
     if (BB.getTerminatingMustTailCall())
diff --git a/llvm/test/Transforms/SimplifyCFG/tail-merge-resume.ll b/llvm/test/Transforms/SimplifyCFG/tail-merge-resume.ll
index 2268f4371ff0..57a057018263 100644
--- a/llvm/test/Transforms/SimplifyCFG/tail-merge-resume.ll
+++ b/llvm/test/Transforms/SimplifyCFG/tail-merge-resume.ll
@@ -39,19 +39,20 @@ define void @merge_simple(i1 %cond) personality i8* bitcast (i32 (...)* @__gxx_p
 ; CHECK-NEXT:    cleanup
 ; CHECK-NEXT:    call void @baz()
 ; CHECK-NEXT:    br label [[RESUME2]]
+; CHECK:       common.resume:
+; CHECK-NEXT:    [[COMMON_RESUME_OP:%.*]] = phi { i8*, i32 } [ [[LP]], [[RESUME0]] ], [ [[LP]], [[RESUME1]] ], [ [[SEMICOMMON_LP:%.*]], [[RESUME2]] ]
+; CHECK-NEXT:    call void @common()
+; CHECK-NEXT:    resume { i8*, i32 } [[COMMON_RESUME_OP]]
 ; CHECK:       resume0:
 ; CHECK-NEXT:    call void @qux()
-; CHECK-NEXT:    call void @common()
-; CHECK-NEXT:    resume { i8*, i32 } [[LP]]
+; CHECK-NEXT:    br label [[COMMON_RESUME:%.*]]
 ; CHECK:       resume1:
 ; CHECK-NEXT:    call void @quux()
-; CHECK-NEXT:    call void @common()
-; CHECK-NEXT:    resume { i8*, i32 } [[LP]]
+; CHECK-NEXT:    br label [[COMMON_RESUME]]
 ; CHECK:       resume2:
-; CHECK-NEXT:    [[SEMICOMMON_LP:%.*]] = phi { i8*, i32 } [ [[LP2]], [[LPAD2]] ], [ [[LP3]], [[LPAD3]] ]
+; CHECK-NEXT:    [[SEMICOMMON_LP]] = phi { i8*, i32 } [ [[LP2]], [[LPAD2]] ], [ [[LP3]], [[LPAD3]] ]
 ; CHECK-NEXT:    call void @quuz()
-; CHECK-NEXT:    call void @common()
-; CHECK-NEXT:    resume { i8*, i32 } [[SEMICOMMON_LP]]
+; CHECK-NEXT:    br label [[COMMON_RESUME]]
 ;
   invoke void @maybe_throws() to label %invoke.cont unwind label %lpad