Index: llvm/trunk/lib/Transforms/Scalar/LICM.cpp
===================================================================
--- llvm/trunk/lib/Transforms/Scalar/LICM.cpp
+++ llvm/trunk/lib/Transforms/Scalar/LICM.cpp
@@ -120,6 +120,7 @@
     bool MayThrow;           // The current loop contains an instruction which
                              // may throw, thus preventing code motion of
                              // instructions with side effects.
+    bool HeaderMayThrow;     // Same as previous, but specific to loop header
     DenseMap<Loop*, AliasSetTracker*> LoopToAliasSetMap;
 
     /// cloneBasicBlockAnalysis - Simple Analysis hook. Clone alias set info.
@@ -273,7 +274,12 @@
       CurAST->add(*BB);                 // Incorporate the specified basic block
   }
 
-  MayThrow = false;
+  HeaderMayThrow = false;
+  BasicBlock *Header = L->getHeader();
+  for (BasicBlock::iterator I = Header->begin(), E = Header->end();
+       (I != E) && !HeaderMayThrow; ++I)
+    HeaderMayThrow |= I->mayThrow();
+  MayThrow = HeaderMayThrow;
   // TODO: We've already searched for instructions which may throw in subloops.
   // We may want to reuse this information.
   for (Loop::block_iterator BB = L->block_begin(), BBE = L->block_end();
@@ -659,12 +665,7 @@
 
 bool LICM::isGuaranteedToExecute(Instruction &Inst) {
 
-  // Somewhere in this loop there is an instruction which may throw and make us
-  // exit the loop.
-  if (MayThrow)
-    return false;
-
-  // Otherwise we have to check to make sure that the instruction dominates all
+  // We have to check to make sure that the instruction dominates all
   // of the exit blocks.  If it doesn't, then there is a path out of the loop
   // which does not execute this instruction, so we can't hoist it.
 
@@ -672,7 +673,14 @@
   // common), it is always guaranteed to dominate the exit blocks.  Since this
   // is a common case, and can save some work, check it now.
   if (Inst.getParent() == CurLoop->getHeader())
-    return true;
+    // If there's a throw in the header block, we can't guarantee we'll reach
+    // Inst.
+    return !HeaderMayThrow;
+
+  // Somewhere in this loop there is an instruction which may throw and make us
+  // exit the loop.
+  if (MayThrow)
+    return false;
 
   // Get the exit blocks for the current loop.
   SmallVector<BasicBlock*, 8> ExitBlocks;
Index: llvm/trunk/test/Transforms/LICM/preheader-safe.ll
===================================================================
--- llvm/trunk/test/Transforms/LICM/preheader-safe.ll
+++ llvm/trunk/test/Transforms/LICM/preheader-safe.ll
@@ -0,0 +1,69 @@
+; RUN: opt -S -licm < %s | FileCheck %s
+
+declare void @use_nothrow(i64 %a) nounwind
+declare void @use(i64 %a)
+
+define void @nothrow(i64 %x, i64 %y, i1* %cond) {
+; CHECK-LABEL: nothrow
+; CHECK-LABEL: entry
+; CHECK: %div = udiv i64 %x, %y
+; CHECK-LABEL: loop
+; CHECK: call void @use_nothrow(i64 %div)
+entry:
+  br label %loop
+
+loop:                                         ; preds = %entry, %for.inc
+  %div = udiv i64 %x, %y
+  call void @use_nothrow(i64 %div)
+  br label %loop
+}
+; Negative test
+define void @throw_header(i64 %x, i64 %y, i1* %cond) {
+; CHECK-LABEL: throw_header
+; CHECK-LABEL: loop
+; CHECK: %div = udiv i64 %x, %y
+; CHECK: call void @use(i64 %div)
+entry:
+  br label %loop
+
+loop:                                         ; preds = %entry, %for.inc
+  %div = udiv i64 %x, %y
+  call void @use(i64 %div)
+  br label %loop
+}
+
+; The header is known no throw, but the loop is not.  We can
+; still lift out of the header.
+define void @nothrow_header(i64 %x, i64 %y, i1 %cond) {
+; CHECK-LABEL: nothrow_header
+; CHECK-LABEL: entry
+; CHECK: %div = udiv i64 %x, %y
+; CHECK-LABEL: loop
+; CHECK: call void @use(i64 %div)
+entry:
+  br label %loop
+loop:                                         ; preds = %entry, %for.inc
+  %div = udiv i64 %x, %y
+  br i1 %cond, label %loop-if, label %exit
+loop-if:
+  call void @use(i64 %div)
+  br label %loop
+exit:
+  ret void
+}
+; Negative test - can't move out of throwing block
+define void @nothrow_header_neg(i64 %x, i64 %y, i1 %cond) {
+; CHECK-LABEL: nothrow_header_neg
+; CHECK-LABEL: entry
+; CHECK-LABEL: loop
+; CHECK: %div = udiv i64 %x, %y
+; CHECK: call void @use(i64 %div)
+entry:
+  br label %loop
+loop:                                         ; preds = %entry, %for.inc
+  br label %loop-if
+loop-if:
+  %div = udiv i64 %x, %y
+  call void @use(i64 %div)
+  br label %loop
+}