When adding blocks to the list of those which no longer have any CFG

conflicts, we should only be adding the first block of the chain to the
list, lest we try to merge into the middle of that chain. Most of the
places we were doing this we already happened to be looking at the first
block, but there is no reason to assume that, and in some cases it was
clearly wrong.

I've added a couple of tests here. One already worked, but I like having
an explicit test for it. The other is reduced from a test case Duncan
reduced for me and used to crash. Now it is handled correctly.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@145119 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/CodeGen/MachineBlockPlacement.cpp b/lib/CodeGen/MachineBlockPlacement.cpp
index 45d5af293039c941d408dbd7793902003213d8f6..870e24884afbdf40b18ad7fe2717fb0bae484abb 100644 (file)
--- a/lib/CodeGen/MachineBlockPlacement.cpp
+++ b/lib/CodeGen/MachineBlockPlacement.cpp
@@ -315,7 +315,7 @@ void MachineBlockPlacement::markChainSuccessors(
       // This is a cross-chain edge that is within the loop, so decrement the
       // loop predecessor count of the destination chain.
       if (SuccChain.LoopPredecessors > 0 && --SuccChain.LoopPredecessors == 0)
-        BlockWorkList.push_back(*SI);
+        BlockWorkList.push_back(*SuccChain.begin());
     }
   }
 }
@@ -594,7 +594,7 @@ void MachineBlockPlacement::buildLoopChains(MachineFunction &F,
     }
 
     if (Chain.LoopPredecessors == 0)
-      BlockWorkList.push_back(*BI);
+      BlockWorkList.push_back(*Chain.begin());
   }
 
   buildChain(*L.block_begin(), LoopChain, BlockWorkList, &LoopBlockSet);
@@ -692,7 +692,7 @@ void MachineBlockPlacement::buildCFGChains(MachineFunction &F) {
     }
 
     if (Chain.LoopPredecessors == 0)
-      BlockWorkList.push_back(BB);
+      BlockWorkList.push_back(*Chain.begin());
   }
 
   BlockChain &FunctionChain = *BlockToChain[&F.front()];

diff --git a/test/CodeGen/X86/block-placement.ll b/test/CodeGen/X86/block-placement.ll
index 891db5a8ce8f60eac64aa78e7a643db07b6f23a5..a6ddc4d68eebb8832662c17253f6730096719164 100644 (file)
--- a/test/CodeGen/X86/block-placement.ll
+++ b/test/CodeGen/X86/block-placement.ll
@@ -593,3 +593,59 @@ exit:
   ret void
 }
 
+define void @unanalyzable_branch_to_best_succ(i1 %cond) {
+; Ensure that we can handle unanalyzable branches where the destination block
+; gets selected as the optimal sucessor to merge.
+;
+; CHECK: unanalyzable_branch_to_best_succ
+; CHECK: %entry
+; CHECK: %foo
+; CHECK: %bar
+; CHECK: %exit
+
+entry:
+  ; Bias this branch toward bar to ensure we form that chain.
+  br i1 %cond, label %bar, label %foo, !prof !1
+
+foo:
+  %cmp = fcmp une double 0.000000e+00, undef
+  br i1 %cmp, label %bar, label %exit
+
+bar:
+  call i32 @f()
+  br label %exit
+
+exit:
+  ret void
+}
+
+define void @unanalyzable_branch_to_free_block(float %x) {
+; Ensure that we can handle unanalyzable branches where the destination block
+; gets selected as the best free block in the CFG.
+;
+; CHECK: unanalyzable_branch_to_free_block
+; CHECK: %entry
+; CHECK: %a
+; CHECK: %b
+; CHECK: %c
+; CHECK: %exit
+
+entry:
+  br i1 undef, label %a, label %b
+
+a:
+  call i32 @f()
+  br label %c
+
+b:
+  %cmp = fcmp une float %x, undef
+  br i1 %cmp, label %c, label %exit
+
+c:
+  call i32 @g()
+  br label %exit
+
+exit:
+  ret void
+}
+