Make simplifycfg reprocess newly formed "br (cond1 | cond2)" conditions

when simplifying, allowing them to be eagerly turned into switches.  This
is the last step required to get "Example 7" from this blog post:
http://blog.regehr.org/archives/320

On X86, we now generate this machine code, which (to my eye) seems better
than the ICC generated code:

_crud:                                  ## @crud
## BB#0:                                ## %entry
	cmpb	$33, %dil
	jb	LBB0_4
## BB#1:                                ## %switch.early.test
	addb	$-34, %dil
	cmpb	$58, %dil
	ja	LBB0_3
## BB#2:                                ## %switch.early.test
	movzbl	%dil, %eax
	movabsq	$288230376537592865, %rcx ## imm = 0x400000017001421
	btq	%rax, %rcx
	jb	LBB0_4
LBB0_3:                                 ## %lor.rhs
	xorl	%eax, %eax
	ret
LBB0_4:                                 ## %lor.end
	movl	$1, %eax
	ret



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@121690 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 12 insertions, 5 deletions

diff --git a/lib/Transforms/Utils/SimplifyCFG.cpp b/lib/Transforms/Utils/SimplifyCFG.cpp
index 503e5bcb23..18c2905a54 100644
--- a/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -1357,7 +1357,7 @@ bool llvm::FoldBranchToCommonDest(BranchInst *BI) {
   // must be at the front of the block.
   BasicBlock::iterator FrontIt = BB->front();
   // Ignore dbg intrinsics.
-  while(isa<DbgInfoIntrinsic>(FrontIt))
+  while (isa<DbgInfoIntrinsic>(FrontIt))
     ++FrontIt;
     
   // Allow a single instruction to be hoisted in addition to the compare
@@ -1441,7 +1441,7 @@ bool llvm::FoldBranchToCommonDest(BranchInst *BI) {
         UsedValues.erase(Pair.first);
         if (UsedValues.empty()) break;
         
-        if (Instruction* I = dyn_cast<Instruction>(Pair.first)) {
+        if (Instruction *I = dyn_cast<Instruction>(Pair.first)) {
           for (Instruction::op_iterator OI = I->op_begin(), OE = I->op_end();
                OI != OE; ++OI)
             Worklist.push_back(std::make_pair(OI->get(), Pair.second+1));
@@ -1469,9 +1469,16 @@ bool llvm::FoldBranchToCommonDest(BranchInst *BI) {
     
     // If we need to invert the condition in the pred block to match, do so now.
     if (InvertPredCond) {
-      Value *NewCond =
-        BinaryOperator::CreateNot(PBI->getCondition(),
+      Value *NewCond = PBI->getCondition();
+      
+      if (NewCond->hasOneUse() && isa<CmpInst>(NewCond)) {
+        CmpInst *CI = cast<CmpInst>(NewCond);
+        CI->setPredicate(CI->getInversePredicate());
+      } else {
+        NewCond = BinaryOperator::CreateNot(NewCond,
                                   PBI->getCondition()->getName()+".not", PBI);
+      }
+      
       PBI->setCondition(NewCond);
       BasicBlock *OldTrue = PBI->getSuccessor(0);
       BasicBlock *OldFalse = PBI->getSuccessor(1);
@@ -1507,7 +1514,7 @@ bool llvm::FoldBranchToCommonDest(BranchInst *BI) {
       AddPredecessorToBlock(FalseDest, PredBlock, BB);
       PBI->setSuccessor(1, FalseDest);
     }
-    return true;
+    return SimplifyCFG(PBI->getParent()) | true;
   }
   return false;
 }