[llvm] r256955 - [ShrinkWrap] Fix FindIDom to only have one kind of failure.

[Michael Kuperstein via llvm-commits]

Author: mkuper
Date: Wed Jan  6 12:40:11 2016
New Revision: 256955

URL: http://llvm.org/viewvc/llvm-project?rev=256955&view=rev
Log:
[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


Added:
    llvm/trunk/test/CodeGen/X86/shrinkwrap-hang.ll
Modified:
    llvm/trunk/lib/CodeGen/ShrinkWrap.cpp

Modified: llvm/trunk/lib/CodeGen/ShrinkWrap.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/ShrinkWrap.cpp?rev=256955&r1=256954&r2=256955&view=diff
==============================================================================
--- llvm/trunk/lib/CodeGen/ShrinkWrap.cpp (original)
+++ llvm/trunk/lib/CodeGen/ShrinkWrap.cpp Wed Jan  6 12:40:11 2016
@@ -263,6 +263,8 @@ MachineBasicBlock *FindIDom(MachineBasic
     if (!IDom)
       break;
   }
+  if (IDom == &Block)
+    return nullptr;
   return IDom;
 }
 
@@ -352,13 +354,9 @@ void ShrinkWrap::updateSaveRestorePoints
       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.

Added: llvm/trunk/test/CodeGen/X86/shrinkwrap-hang.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/X86/shrinkwrap-hang.ll?rev=256955&view=auto
==============================================================================
--- llvm/trunk/test/CodeGen/X86/shrinkwrap-hang.ll (added)
+++ llvm/trunk/test/CodeGen/X86/shrinkwrap-hang.ll Wed Jan  6 12:40:11 2016
@@ -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"
+
+ at b = global i32 1, align 4
+ at 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" }