From: Michael Kuperstein <michael.m.kuperstein@intel.com>
Date: Wed, 6 Jan 2016 18:40:11 +0000 (+0000)
Subject: [ShrinkWrap] Fix FindIDom to only have one kind of failure.
X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=f8ab3ef1eb83f2fdbe54924ba8a46646e3421193;p=oota-llvm.git

[ShrinkWrap] Fix FindIDom to only have one kind of failure.

FindIDom() can fail in two different ways - it can either return nullptr or the
block itself, depending on the circumstances. Some users of FindIDom() check
one error condition, while others check the other.

Change it to always return nullptr on failure.
This fixes PR26004.

Differential Revision: http://reviews.llvm.org/D15847



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@256955 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/lib/CodeGen/ShrinkWrap.cpp b/lib/CodeGen/ShrinkWrap.cpp
index f8aa1e2b0b9..2ff86aaa51c 100644
--- a/lib/CodeGen/ShrinkWrap.cpp
+++ b/lib/CodeGen/ShrinkWrap.cpp
@@ -263,6 +263,8 @@ MachineBasicBlock *FindIDom(MachineBasicBlock &Block, ListOfBBs BBs,
     if (!IDom)
       break;
   }
+  if (IDom == &Block)
+    return nullptr;
   return IDom;
 }
 
@@ -352,13 +354,9 @@ void ShrinkWrap::updateSaveRestorePoints(MachineBasicBlock &MBB,
       if (MLI->getLoopDepth(Save) > MLI->getLoopDepth(Restore)) {
         // Push Save outside of this loop if immediate dominator is different
         // from save block. If immediate dominator is not different, bail out.
-        MachineBasicBlock *IDom = FindIDom<>(*Save, Save->predecessors(), *MDT);
-        if (IDom != Save)
-          Save = IDom;
-        else {
-          Save = nullptr;
+        Save = FindIDom<>(*Save, Save->predecessors(), *MDT);
+        if (!Save)
           break;
-        }
       } else {
         // If the loop does not exit, there is no point in looking
         // for a post-dominator outside the loop.
diff --git a/test/CodeGen/X86/shrinkwrap-hang.ll b/test/CodeGen/X86/shrinkwrap-hang.ll
new file mode 100644
index 00000000000..e1e4eefb3ef
--- /dev/null
+++ b/test/CodeGen/X86/shrinkwrap-hang.ll
@@ -0,0 +1,32 @@
+; RUN: llc %s -o - -enable-shrink-wrap=true | FileCheck %s
+
+target datalayout = "e-m:e-p:32:32-f64:32:64-f80:32-n8:16:32-S128"
+target triple = "i686-pc-linux"
+
+@b = global i32 1, align 4
+@a = common global i32 0, align 4
+
+declare void @fn1() #0
+
+; CHECK-LABEL: fn2:
+define void @fn2() #0 {
+entry:
+  %0 = load i32, i32* @b, align 4
+  %tobool = icmp eq i32 %0, 0
+  br i1 %tobool, label %if.end, label %lbl
+
+lbl:                                              ; preds = %if.end, %entry
+  store i32 0, i32* @b, align 4
+  br label %if.end
+
+if.end:                                           ; preds = %entry, %lbl
+  tail call void @fn1()
+  %1 = load i32, i32* @b, align 4
+  %tobool1 = icmp eq i32 %1, 0
+  br i1 %tobool1, label %if.end3, label %lbl
+
+if.end3:                                          ; preds = %if.end
+  ret void
+}
+
+attributes #0 = { norecurse nounwind "disable-tail-calls"="false" "less-precise-fpmad"="false" "no-frame-pointer-elim"="false" "no-infs-fp-math"="false" "no-nans-fp-math"="false" "stack-protector-buffer-size"="8" "target-cpu"="pentium4" "target-features"="+fxsr,+mmx,+sse,+sse2" "unsafe-fp-math"="false" "use-soft-float"="false" }