Add a parameter to ConstantFoldTerminator() that callers can use to ask it to also...

I also changed -simplifycfg, -jump-threading and -codegenprepare to use this to produce slightly better code without any extra cleanup passes (AFAICT this was the only place in -simplifycfg where now-dead conditions of replaced terminators weren't being cleaned up). The only other user of this function is -sccp, but I didn't read that thoroughly enough to figure out whether it might be holding pointers to instructions that could be deleted by this.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@131855 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/include/llvm/Transforms/Utils/Local.h b/include/llvm/Transforms/Utils/Local.h
index e61dcb347c85d24dae1aafaaba35c64ea6f0fb93..c9d29168217aa63c7150185f334916eb4c7fd0db 100644 (file)
--- a/include/llvm/Transforms/Utils/Local.h
+++ b/include/llvm/Transforms/Utils/Local.h
@@ -43,8 +43,10 @@ template<typename T> class SmallVectorImpl;
 /// constant value, convert it into an unconditional branch to the constant
 /// destination.  This is a nontrivial operation because the successors of this
 /// basic block must have their PHI nodes updated.
-///
-bool ConstantFoldTerminator(BasicBlock *BB);
+/// Also calls RecursivelyDeleteTriviallyDeadInstructions() on any branch/switch
+/// conditions and indirectbr addresses this might make dead if
+/// DeleteDeadConditions is true.
+bool ConstantFoldTerminator(BasicBlock *BB, bool DeleteDeadConditions = false);
 
 //===----------------------------------------------------------------------===//
 //  Local dead code elimination.

diff --git a/lib/Transforms/Scalar/CodeGenPrepare.cpp b/lib/Transforms/Scalar/CodeGenPrepare.cpp
index 018439018553be5fca6891639f85f67a848b6093..483bfe36552a041cc9beb000a0de32d3c30c0b8b 100644 (file)
--- a/lib/Transforms/Scalar/CodeGenPrepare.cpp
+++ b/lib/Transforms/Scalar/CodeGenPrepare.cpp
@@ -147,7 +147,7 @@ bool CodeGenPrepare::runOnFunction(Function &F) {
   if (!DisableBranchOpts) {
     MadeChange = false;
     for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB)
-      MadeChange |= ConstantFoldTerminator(BB);
+      MadeChange |= ConstantFoldTerminator(BB, true);
 
     if (MadeChange)
       ModifiedDT = true;

diff --git a/lib/Transforms/Scalar/JumpThreading.cpp b/lib/Transforms/Scalar/JumpThreading.cpp
index 5a8f4ca192d544517b22bf38cdd52786425e89c5..cf18ff040bdab2b6f871c7d5f6f0e699006db1f5 100644 (file)
--- a/lib/Transforms/Scalar/JumpThreading.cpp
+++ b/lib/Transforms/Scalar/JumpThreading.cpp
@@ -706,7 +706,7 @@ bool JumpThreading::ProcessBlock(BasicBlock *BB) {
     DEBUG(dbgs() << "  In block '" << BB->getName()
           << "' folding terminator: " << *BB->getTerminator() << '\n');
     ++NumFolds;
-    ConstantFoldTerminator(BB);
+    ConstantFoldTerminator(BB, true);
     return true;
   }
 

diff --git a/lib/Transforms/Scalar/SimplifyCFGPass.cpp b/lib/Transforms/Scalar/SimplifyCFGPass.cpp
index 1137c2b23f964083afb4ec6f1b16edee969ffb0d..eccafea3aa89961acb535bd1362936bdc85d3fee 100644 (file)
--- a/lib/Transforms/Scalar/SimplifyCFGPass.cpp
+++ b/lib/Transforms/Scalar/SimplifyCFGPass.cpp
@@ -163,7 +163,7 @@ static bool MarkAliveBlocks(BasicBlock *BB,
         Changed = true;
       }
 
-    Changed |= ConstantFoldTerminator(BB);
+    Changed |= ConstantFoldTerminator(BB, true);
     for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB); SI != SE; ++SI)
       Worklist.push_back(*SI);
   } while (!Worklist.empty());

diff --git a/lib/Transforms/Utils/Local.cpp b/lib/Transforms/Utils/Local.cpp
index 12e15b07c79d391420218ee512b5da0c62d68693..f5a8adacd5aba0773cb9915f77e0dcb7767bcf1b 100644 (file)
--- a/lib/Transforms/Utils/Local.cpp
+++ b/lib/Transforms/Utils/Local.cpp
@@ -44,11 +44,14 @@ using namespace llvm;
 //  Local constant propagation.
 //
 
-// ConstantFoldTerminator - If a terminator instruction is predicated on a
-// constant value, convert it into an unconditional branch to the constant
-// destination.
-//
-bool llvm::ConstantFoldTerminator(BasicBlock *BB) {
+/// ConstantFoldTerminator - If a terminator instruction is predicated on a
+/// constant value, convert it into an unconditional branch to the constant
+/// destination.  This is a nontrivial operation because the successors of this
+/// basic block must have their PHI nodes updated.
+/// Also calls RecursivelyDeleteTriviallyDeadInstructions() on any branch/switch
+/// conditions and indirectbr addresses this might make dead if
+/// DeleteDeadConditions is true.
+bool llvm::ConstantFoldTerminator(BasicBlock *BB, bool DeleteDeadConditions) {
   TerminatorInst *T = BB->getTerminator();
   IRBuilder<> Builder(T);
 
@@ -89,7 +92,10 @@ bool llvm::ConstantFoldTerminator(BasicBlock *BB) {
 
       // Replace the conditional branch with an unconditional one.
       Builder.CreateBr(Dest1);
+      Value *Cond = BI->getCondition();
       BI->eraseFromParent();
+      if (DeleteDeadConditions)
+        RecursivelyDeleteTriviallyDeadInstructions(Cond);
       return true;
     }
     return false;
@@ -152,7 +158,10 @@ bool llvm::ConstantFoldTerminator(BasicBlock *BB) {
       }
 
       // Delete the old switch.
-      BB->getInstList().erase(SI);
+      Value *Cond = SI->getCondition();
+      SI->eraseFromParent();
+      if (DeleteDeadConditions)
+        RecursivelyDeleteTriviallyDeadInstructions(Cond);
       return true;
     }
     
@@ -186,7 +195,10 @@ bool llvm::ConstantFoldTerminator(BasicBlock *BB) {
         else
           IBI->getDestination(i)->removePredecessor(IBI->getParent());
       }
+      Value *Address = IBI->getAddress();
       IBI->eraseFromParent();
+      if (DeleteDeadConditions)
+        RecursivelyDeleteTriviallyDeadInstructions(Address);
       
       // If we didn't find our destination in the IBI successor list, then we
       // have undefined behavior.  Replace the unconditional branch with an

diff --git a/lib/Transforms/Utils/SimplifyCFG.cpp b/lib/Transforms/Utils/SimplifyCFG.cpp
index 2c032d5d1293447e6995cf5927068c3f61b7d70f..5ab9a2877cd503f3b834be873ce64467c03cea1f 100644 (file)
--- a/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -2651,7 +2651,7 @@ bool SimplifyCFGOpt::run(BasicBlock *BB) {
 
   // Check to see if we can constant propagate this terminator instruction
   // away...
-  Changed |= ConstantFoldTerminator(BB);
+  Changed |= ConstantFoldTerminator(BB, true);
 
   // Check for and eliminate duplicate PHI nodes in this block.
   Changed |= EliminateDuplicatePHINodes(BB);

diff --git a/test/Transforms/SimplifyCFG/dce-cond-after-folding-terminator.ll b/test/Transforms/SimplifyCFG/dce-cond-after-folding-terminator.ll
new file mode 100644 (file)
index 0000000..3996efd
--- /dev/null
+++ b/test/Transforms/SimplifyCFG/dce-cond-after-folding-terminator.ll
@@ -0,0 +1,52 @@
+; RUN: opt -S <%s -simplifycfg | FileCheck %s
+
+define void @test_br(i32 %x) {
+entry:
+; CHECK: @test_br
+; CHECK-NEXT: entry:
+; CHECK-NEXT: ret void
+  %cmp = icmp eq i32 %x, 10
+  br i1 %cmp, label %if.then, label %if.then
+
+if.then:                                          ; preds = %entry
+  br label %if.end
+
+if.end:                                           ; preds = %if.else, %if.then
+  ret void
+}
+
+define void @test_switch(i32 %x) nounwind {
+entry:
+; CHECK: @test_switch
+; CHECK-NEXT: entry:
+; CHECK-NEXT: ret void
+  %rem = srem i32 %x, 3
+  switch i32 %rem, label %sw.bb [
+    i32 1, label %sw.bb
+    i32 10, label %sw.bb
+  ]
+
+sw.bb:                                            ; preds = %sw.default, %entry, %entry
+  br label %sw.epilog
+
+sw.epilog:                                        ; preds = %sw.bb
+  ret void
+}
+
+define void @test_indirectbr(i32 %x) {
+entry:
+; CHECK: @test_indirectbr
+; CHECK-NEXT: entry:
+; Ideally this should now check:
+;   CHK-NEXT: ret void
+; But that doesn't happen yet. Instead:
+; CHECK-NEXT: br label %L1
+
+  %label = bitcast i8* blockaddress(@test_indirectbr, %L1) to i8*
+  indirectbr i8* %label, [label %L1, label %L2]
+
+L1:                                               ; preds = %entry
+  ret void
+L2:                                               ; preds = %entry
+  ret void
+}