[llvm] r279499 - BranchRelaxation: Fix handling of blocks with multiple conditional

[Matt Arsenault via llvm-commits]

Author: arsenm
Date: Mon Aug 22 20:30:30 2016
New Revision: 279499

URL: http://llvm.org/viewvc/llvm-project?rev=279499&view=rev
Log:
BranchRelaxation: Fix handling of blocks with multiple conditional
branches

Looping over all terminators exposed AArch64 tests hitting
an assert from analyzeBranch failing. I believe these cases
were miscompiled before.

e.g.
  fcmp s0, s1
  b.ne LBB0_1
  b.vc LBB0_2
  b LBB0_2
LBB0_1:
  ; Large block
LBB0_2:
 ; ...

Both of the individual conditional branches need to
be expanded, since neither can reach the final block.

Split the original block into ones which analyzeBranch
will be able to understand.

Modified:
    llvm/trunk/lib/Target/AArch64/AArch64BranchRelaxation.cpp
    llvm/trunk/test/CodeGen/AArch64/branch-relax-bcc.ll

Modified: llvm/trunk/lib/Target/AArch64/AArch64BranchRelaxation.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/AArch64/AArch64BranchRelaxation.cpp?rev=279499&r1=279498&r2=279499&view=diff
==============================================================================
--- llvm/trunk/lib/Target/AArch64/AArch64BranchRelaxation.cpp (original)
+++ llvm/trunk/lib/Target/AArch64/AArch64BranchRelaxation.cpp Mon Aug 22 20:30:30 2016
@@ -25,7 +25,7 @@ using namespace llvm;
 #define DEBUG_TYPE "aarch64-branch-relax"
 
 STATISTIC(NumSplit, "Number of basic blocks split");
-STATISTIC(NumRelaxed, "Number of conditional branches relaxed");
+STATISTIC(NumConditionalRelaxed, "Number of conditional branches relaxed");
 
 namespace llvm {
 void initializeAArch64BranchRelaxationPass(PassRegistry &);
@@ -477,13 +477,43 @@ bool AArch64BranchRelaxation::relaxBranc
     if (J == MBB.end())
       continue;
 
-    MachineInstr &MI = *J;
-    if (MI.isConditionalBranch() && !isBlockInRange(MI, *getDestBlock(MI))) {
-      fixupConditionalBranch(MI);
-      ++NumRelaxed;
-      Changed = true;
+    MachineBasicBlock::iterator Next;
+    for (MachineBasicBlock::iterator J = MBB.getFirstTerminator();
+         J != MBB.end(); J = Next) {
+      Next = std::next(J);
+      MachineInstr &MI = *J;
+
+      if (MI.isConditionalBranch()) {
+        MachineBasicBlock *DestBB = getDestBlock(MI);
+        if (!isBlockInRange(MI, *DestBB)) {
+          if (Next != MBB.end() && Next->isConditionalBranch()) {
+            // If there are multiple conditional branches, this isn't an
+            // analyzable block. Split later terminators into a new block so
+            // each one will be analyzable.
+
+            MachineBasicBlock *NewBB = splitBlockBeforeInstr(*Next);
+            NewBB->transferSuccessors(&MBB);
+            MBB.addSuccessor(NewBB);
+            MBB.addSuccessor(DestBB);
+
+            // Cleanup potential unconditional branch to successor block.
+            NewBB->updateTerminator();
+            MBB.updateTerminator();
+          } else {
+            fixupConditionalBranch(MI);
+            ++NumConditionalRelaxed;
+          }
+
+          Changed = true;
+
+          // This may have modified all of the terminators, so start over.
+          Next = MBB.getFirstTerminator();
+        }
+
+      }
     }
   }
+
   return Changed;
 }
 

Modified: llvm/trunk/test/CodeGen/AArch64/branch-relax-bcc.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/AArch64/branch-relax-bcc.ll?rev=279499&r1=279498&r2=279499&view=diff
==============================================================================
--- llvm/trunk/test/CodeGen/AArch64/branch-relax-bcc.ll (original)
+++ llvm/trunk/test/CodeGen/AArch64/branch-relax-bcc.ll Mon Aug 22 20:30:30 2016
@@ -1,16 +1,22 @@
 ; RUN: llc -mtriple=aarch64-apple-darwin -aarch64-bcc-offset-bits=3 < %s | FileCheck %s
 
 ; CHECK-LABEL: invert_bcc:
-; CHECK:       fcmp s0, s1
-; CHECK-NEXT:  b.ne [[BB1:LBB[0-9]+_[0-9]+]]
-; CHECK-NEXT:  b.vs [[BB2:LBB[0-9]+_[0-9]+]]
-; CHECK-NEXT:  b [[BB2]]
+; CHECK:      fcmp s0, s1
+; CHECK-NEXT: b.eq [[JUMP_BB1:LBB[0-9]+_[0-9]+]]
+; CHECK-NEXT: b [[JUMP_BB2:LBB[0-9]+_[0-9]+]]
 
-; CHECK: [[BB1]]:
+; CHECK-NEXT: [[JUMP_BB1]]:
+; CHECK-NEXT: b [[BB1:LBB[0-9]+_[0-9]+]]
+
+; CHECK-NEXT: [[JUMP_BB2]]:
+; CHECK-NEXT: b.vc [[BB2:LBB[0-9]+_[0-9]+]]
+; CHECK-NEXT: b [[BB1]]
+
+; CHECK: [[BB2]]: ; %bb2
 ; CHECK: mov w{{[0-9]+}}, #9
 ; CHECK: ret
 
-; CHECK: [[BB2]]:
+; CHECK: [[BB1]]: ; %bb1
 ; CHECK: mov w{{[0-9]+}}, #42
 ; CHECK: ret