reland: [Local] Allow creating callbr with duplicate successors

Since D129288, callbr is allowed to have duplicate successors. This patch removes a limitation which prevents optimizations from actually producing such callbrs.

This is probably the riskiest of all the recent callbr changes, because code with incorrect assumptions might be lurking somewhere. I fixed the one case I encountered ahead of time in https://github.com/llvm/llvm-project/commit/8201e3ef5c84561260218bc041209611aac690e3.

Reviewed By: nickdesaulniers

Differential Revision: https://reviews.llvm.org/D129997

Originally landed as
commit 08860f525a23 ("[Local] Allow creating callbr with duplicate successors")

Reverted in
commit 1cf6b93df168 ("Revert "[Local] Allow creating callbr with duplicate successors"")

diff --git a/llvm/lib/Transforms/Utils/Local.cpp b/llvm/lib/Transforms/Utils/Local.cpp
index c1735f7..1115b0b 100644 (file)
--- a/llvm/lib/Transforms/Utils/Local.cpp
+++ b/llvm/lib/Transforms/Utils/Local.cpp
@@ -1090,18 +1090,6 @@ bool llvm::TryToSimplifyUncondBranchFromEmptyBlock(BasicBlock *BB,
     }
   }
 
-  // We cannot fold the block if it's a branch to an already present callbr
-  // successor because that creates duplicate successors.
-  for (BasicBlock *PredBB : predecessors(BB)) {
-    if (auto *CBI = dyn_cast<CallBrInst>(PredBB->getTerminator())) {
-      if (Succ == CBI->getDefaultDest())
-        return false;
-      for (unsigned i = 0, e = CBI->getNumIndirectDests(); i != e; ++i)
-        if (Succ == CBI->getIndirectDest(i))
-          return false;
-    }
-  }
-
   LLVM_DEBUG(dbgs() << "Killing Trivial BB: \n" << *BB);
 
   SmallVector<DominatorTree::UpdateType, 32> Updates;

diff --git a/llvm/test/CodeGen/AArch64/callbr-asm-obj-file.ll b/llvm/test/CodeGen/AArch64/callbr-asm-obj-file.ll
index 06d9568..803b15d 100644 (file)
--- a/llvm/test/CodeGen/AArch64/callbr-asm-obj-file.ll
+++ b/llvm/test/CodeGen/AArch64/callbr-asm-obj-file.ll
@@ -72,9 +72,8 @@ define hidden i32 @test2() local_unnamed_addr {
 ; CHECK-LABEL: <test3>:
 ; CHECK-LABEL: <$d.9>:
 ; CHECK-LABEL: <$x.10>:
-; CHECK-NEXT:    b {{.*}} <$x.12+0x4>
+; CHECK-NEXT:    b {{.*}} <$x.12>
 ; CHECK-LABEL: <$x.12>:
-; CHECK-NEXT:    mov w0, wzr
 ; CHECK-NEXT:    ldr x30, [sp], #16
 ; CHECK-NEXT:    ret
 define internal i1 @test3() {

diff --git a/llvm/test/Transforms/JumpThreading/callbr-edge-split.ll b/llvm/test/Transforms/JumpThreading/callbr-edge-split.ll
index 7d1cb4c..d96f5cf 100644 (file)
--- a/llvm/test/Transforms/JumpThreading/callbr-edge-split.ll
+++ b/llvm/test/Transforms/JumpThreading/callbr-edge-split.ll
@@ -13,9 +13,7 @@ define i32 @c() {
 ; CHECK-NEXT:    br i1 [[TOBOOL]], label [[IF_ELSE:%.*]], label [[IF_END:%.*]]
 ; CHECK:       if.else:
 ; CHECK-NEXT:    callbr void asm sideeffect "", "!i"()
-; CHECK-NEXT:    to label [[NORMAL:%.*]] [label %if.then2]
-; CHECK:       normal:
-; CHECK-NEXT:    br label [[IF_THEN2:%.*]]
+; CHECK-NEXT:    to label [[IF_THEN2:%.*]] [label %if.then2]
 ; CHECK:       if.end:
 ; CHECK-NEXT:    [[CALL:%.*]] = call i32 @b()
 ; CHECK-NEXT:    [[PHITMP:%.*]] = icmp ne i32 [[CALL]], 0

diff --git a/llvm/test/Transforms/JumpThreading/pr46857-callbr.ll b/llvm/test/Transforms/JumpThreading/pr46857-callbr.ll
index a5ccde0..f1d0629 100644 (file)
--- a/llvm/test/Transforms/JumpThreading/pr46857-callbr.ll
+++ b/llvm/test/Transforms/JumpThreading/pr46857-callbr.ll
@@ -1,17 +1,13 @@
 ; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
 ; RUN: opt < %s -jump-threading -S | FileCheck %s
 
-; CHECK-ALL-LABEL: @func(
-
 define i1 @func(i1 %arg, i32 %arg1, i1 %arg2) {
 ; CHECK-LABEL: @func(
 ; CHECK-NEXT:  bb:
 ; CHECK-NEXT:    br i1 [[ARG:%.*]], label [[BB7:%.*]], label [[BB4:%.*]]
 ; CHECK:       bb4:
 ; CHECK-NEXT:    callbr void asm sideeffect "", "!i"()
-; CHECK-NEXT:    to label [[BB5:%.*]] [label %bb7.thr_comm]
-; CHECK:       bb5:
-; CHECK-NEXT:    br label [[BB7_THR_COMM:%.*]]
+; CHECK-NEXT:    to label [[BB7_THR_COMM:%.*]] [label %bb7.thr_comm]
 ; CHECK:       bb7.thr_comm:
 ; CHECK-NEXT:    [[I91:%.*]] = xor i1 [[ARG2:%.*]], [[ARG]]
 ; CHECK-NEXT:    br i1 [[I91]], label [[BB11:%.*]], label [[BB11]]

diff --git a/llvm/test/Transforms/SimplifyCFG/callbr-destinations.ll b/llvm/test/Transforms/SimplifyCFG/callbr-destinations.ll
index 368bc5e..008aa5c 100644 (file)
--- a/llvm/test/Transforms/SimplifyCFG/callbr-destinations.ll
+++ b/llvm/test/Transforms/SimplifyCFG/callbr-destinations.ll
@@ -17,16 +17,13 @@ bb:
   ret void
 }
 
-; TODO: Can fold to a duplicate callbr destination.
 define void @callbr_can_fold_to_duplicate_dest1() {
 ; CHECK-LABEL: @callbr_can_fold_to_duplicate_dest1(
 ; CHECK-NEXT:  entry:
 ; CHECK-NEXT:    callbr void asm sideeffect "", "!i"()
-; CHECK-NEXT:    to label [[BB2:%.*]] [label %common.ret]
+; CHECK-NEXT:    to label [[COMMON_RET:%.*]] [label %common.ret]
 ; CHECK:       common.ret:
 ; CHECK-NEXT:    ret void
-; CHECK:       bb2:
-; CHECK-NEXT:    br label [[COMMON_RET:%.*]]
 ;
 entry:
   callbr void asm sideeffect "", "!i"()
@@ -39,18 +36,13 @@ bb2:
   ret void
 }
 
-; TODO: Can fold to a duplicate callbr destination.
 define void @callbr_can_fold_to_duplicate_dest2() {
 ; CHECK-LABEL: @callbr_can_fold_to_duplicate_dest2(
 ; CHECK-NEXT:  entry:
 ; CHECK-NEXT:    callbr void asm sideeffect "", "!i,!i"()
-; CHECK-NEXT:    to label [[COMMON_RET:%.*]] [label [[BB2:%.*]], label %bb3]
+; CHECK-NEXT:    to label [[COMMON_RET:%.*]] [label [[COMMON_RET]], label %common.ret]
 ; CHECK:       common.ret:
 ; CHECK-NEXT:    ret void
-; CHECK:       bb2:
-; CHECK-NEXT:    br label [[COMMON_RET]]
-; CHECK:       bb3:
-; CHECK-NEXT:    br label [[COMMON_RET]]
 ;
 entry:
   callbr void asm sideeffect "", "!i,!i"()

diff --git a/llvm/test/Transforms/SimplifyCFG/jump-threading.ll b/llvm/test/Transforms/SimplifyCFG/jump-threading.ll
index e7d7662..96befcc 100644 (file)
--- a/llvm/test/Transforms/SimplifyCFG/jump-threading.ll
+++ b/llvm/test/Transforms/SimplifyCFG/jump-threading.ll
@@ -425,9 +425,7 @@ define void @callbr() {
 ; CHECK-LABEL: @callbr(
 ; CHECK-NEXT:  entry:
 ; CHECK-NEXT:    callbr void asm sideeffect "", "!i,~{dirflag},~{fpsr},~{flags}"()
-; CHECK-NEXT:    to label [[IF_END:%.*]] [label %target]
-; CHECK:       target:
-; CHECK-NEXT:    br label [[IF_END]]
+; CHECK-NEXT:    to label [[IF_END:%.*]] [label %if.end]
 ; CHECK:       if.end:
 ; CHECK-NEXT:    ret void
 ;