[llvm-commits] [llvm] r101870 - in /llvm/trunk: lib/Transforms/Scalar/LoopUnswitch.cpp test/Transforms/LoopUnswitch/crash.ll

[Chris Lattner]

Author: lattner
Date: Tue Apr 20 00:09:16 2010
New Revision: 101870

URL: http://llvm.org/viewvc/llvm-project?rev=101870&view=rev
Log:
RewriteLoopBodyWithConditionConstant can end up rewriting the
condition we're unswitching on.  In this case, don't try to
simplify the second copy of the loop which may be dead or not,
but is probably a constant now.  This fixes PR6879

Modified:
    llvm/trunk/lib/Transforms/Scalar/LoopUnswitch.cpp
    llvm/trunk/test/Transforms/LoopUnswitch/crash.ll

Modified: llvm/trunk/lib/Transforms/Scalar/LoopUnswitch.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/LoopUnswitch.cpp?rev=101870&r1=101869&r2=101870&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Scalar/LoopUnswitch.cpp (original)
+++ llvm/trunk/lib/Transforms/Scalar/LoopUnswitch.cpp Tue Apr 20 00:09:16 2010
@@ -677,15 +677,22 @@
   LoopProcessWorklist.push_back(NewLoop);
   redoLoop = true;
 
+  // Keep a WeakVH holding onto LIC.  If the first call to RewriteLoopBody
+  // deletes the instruction (for example by simplifying a PHI that feeds into
+  // the condition that we're unswitching on), we don't rewrite the second
+  // iteration.
+  WeakVH LICHandle(LIC);
+  
   // Now we rewrite the original code to know that the condition is true and the
   // new code to know that the condition is false.
   RewriteLoopBodyWithConditionConstant(L, LIC, Val, false);
-  
-  // It's possible that simplifying one loop could cause the other to be
-  // deleted.  If so, don't simplify it.
-  if (!LoopProcessWorklist.empty() && LoopProcessWorklist.back() == NewLoop)
-    RewriteLoopBodyWithConditionConstant(NewLoop, LIC, Val, true);
 
+  // It's possible that simplifying one loop could cause the other to be
+  // changed to another value or a constant.  If its a constant, don't simplify
+  // it.
+  if (!LoopProcessWorklist.empty() && LoopProcessWorklist.back() == NewLoop &&
+      LICHandle && !isa<Constant>(LICHandle))
+    RewriteLoopBodyWithConditionConstant(NewLoop, LICHandle, Val, true);
 }
 
 /// RemoveFromWorklist - Remove all instances of I from the worklist vector
@@ -981,6 +988,8 @@
       continue;
     }
     
+    // FIXME: Change this to use instruction simplify interfaces!
+    
     // Special case hacks that appear commonly in unswitched code.
     switch (I->getOpcode()) {
     case Instruction::Select:

Modified: llvm/trunk/test/Transforms/LoopUnswitch/crash.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/LoopUnswitch/crash.ll?rev=101870&r1=101869&r2=101870&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/LoopUnswitch/crash.ll (original)
+++ llvm/trunk/test/Transforms/LoopUnswitch/crash.ll Tue Apr 20 00:09:16 2010
@@ -45,3 +45,22 @@
 for.end:                                          ; preds = %for.body, %entry
   ret void
 }
+
+; PR6879
+define i32* @test3(i32** %p_45, i16 zeroext %p_46, i64 %p_47, i64 %p_48, i16 signext %p_49) nounwind {
+entry:
+  br label %for.cond
+
+for.cond:                                         ; preds = %for.cond4, %entry
+  br i1 false, label %for.cond4, label %for.end88
+
+for.cond4:                                        ; preds = %for.cond
+  %conv46 = trunc i32 0 to i8                     ; <i8> [#uses=2]
+  %cmp60 = icmp sgt i8 %conv46, 124               ; <i1> [#uses=1]
+  %or.cond = and i1 undef, %cmp60                 ; <i1> [#uses=1]
+  %cond = select i1 %or.cond, i8 %conv46, i8 undef ; <i8> [#uses=0]
+  br label %for.cond
+
+for.end88:                                        ; preds = %for.cond
+  ret i32* undef
+}