[llvm-commits] [llvm] r145100 - in /llvm/trunk: lib/CodeGen/MachineBlockPlacement.cpp test/CodeGen/X86/block-placement.ll

[Chandler Carruth]

Author: chandlerc
Date: Wed Nov 23 04:35:36 2011
New Revision: 145100

URL: http://llvm.org/viewvc/llvm-project?rev=145100&view=rev
Log:
Relax an invariant that block placement was trying to assert a bit
further. This invariant just wasn't going to work in the face of
unanalyzable branches; we need to be resillient to the phenomenon of
chains poking into a loop and poking out of a loop. In fact, we already
were, we just needed to not assert on it.

This was found during a bootstrap with block placement turned on.

Modified:
    llvm/trunk/lib/CodeGen/MachineBlockPlacement.cpp
    llvm/trunk/test/CodeGen/X86/block-placement.ll

Modified: llvm/trunk/lib/CodeGen/MachineBlockPlacement.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/MachineBlockPlacement.cpp?rev=145100&r1=145099&r2=145100&view=diff
==============================================================================
--- llvm/trunk/lib/CodeGen/MachineBlockPlacement.cpp (original)
+++ llvm/trunk/lib/CodeGen/MachineBlockPlacement.cpp Wed Nov 23 04:35:36 2011
@@ -504,7 +504,6 @@
     const BlockFilterSet *BlockFilter) {
   assert(BB);
   assert(BlockToChain[BB] == &Chain);
-  assert(*Chain.begin() == BB);
   MachineFunction &F = *BB->getParent();
   MachineFunction::iterator PrevUnplacedBlockIt = F.begin();
 
@@ -614,8 +613,7 @@
       if (!LoopBlockSet.erase(*BCI)) {
         // We don't mark the loop as bad here because there are real situations
         // where this can occur. For example, with an unanalyzable fallthrough
-        // from a loop block to a non-loop block.
-        // FIXME: Such constructs shouldn't exist. Track them down and fix them.
+        // from a loop block to a non-loop block or vice versa.
         dbgs() << "Loop chain contains a block not contained by the loop!\n"
                << "  Loop header:  " << getBlockName(*L.block_begin()) << "\n"
                << "  Chain header: " << getBlockName(*LoopChain.begin()) << "\n"

Modified: llvm/trunk/test/CodeGen/X86/block-placement.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/X86/block-placement.ll?rev=145100&r1=145099&r2=145100&view=diff
==============================================================================
--- llvm/trunk/test/CodeGen/X86/block-placement.ll (original)
+++ llvm/trunk/test/CodeGen/X86/block-placement.ll Wed Nov 23 04:35:36 2011
@@ -568,3 +568,28 @@
   %next.phi = phi i32* [ %next.load, %loop2b ], [ %next.var, %loop2a ]
   br label %loop1
 }
+
+define void @unanalyzable_branch_to_loop_header() {
+; Ensure that we can handle unanalyzable branches into loop headers. We
+; pre-form chains for unanalyzable branches, and will find the tail end of that
+; at the start of the loop. This function uses floating point comparison
+; fallthrough because that happens to always produce unanalyzable branches on
+; x86.
+;
+; CHECK: unanalyzable_branch_to_loop_header
+; CHECK: %entry
+; CHECK: %loop
+; CHECK: %exit
+
+entry:
+  %cmp = fcmp une double 0.000000e+00, undef
+  br i1 %cmp, label %loop, label %exit
+
+loop:
+  %cond = icmp eq i8 undef, 42
+  br i1 %cond, label %exit, label %loop
+
+exit:
+  ret void
+}
+