Don't merge uses when they are targetting fixup sites with

different widths. In a use with a narrower fixup, formulae
may be wider than the fixup, in which case the high bits
aren't necessarily meaningful, so it isn't safe to reuse
them for uses with wider fixups.

This fixes PR7618, though the testcase is too large for a
reasonable regression test, since it heavily dependes on
hitting LSR's heuristics in a certain way.

llvm-svn: 108455

1 files changed, 20 insertions, 1 deletions

diff --git a/llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp b/llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp
index 1612d895f21..adaadb26e9b 100644
--- a/llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp
+++ b/llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp
@@ -965,6 +965,12 @@ public:
   /// may be used.
   bool AllFixupsOutsideLoop;
 
+  /// WidestFixupType - This records the widest use type for any fixup using
+  /// this LSRUse. FindUseWithSimilarFormula can't consider uses with different
+  /// max fixup widths to be equivalent, because the narrower one may be relying
+  /// on the implicit truncation to truncate away bogus bits.
+  const Type *WidestFixupType;
+
   /// Formulae - A list of ways to build a value that can satisfy this user.
   /// After the list is populated, one of these is selected heuristically and
   /// used to formulate a replacement for OperandValToReplace in UserInst.
@@ -976,7 +982,8 @@ public:
   LSRUse(KindType K, const Type *T) : Kind(K), AccessTy(T),
                                       MinOffset(INT64_MAX),
                                       MaxOffset(INT64_MIN),
-                                      AllFixupsOutsideLoop(true) {}
+                                      AllFixupsOutsideLoop(true),
+                                      WidestFixupType(0) {}
 
   bool HasFormulaWithSameRegs(const Formula &F) const;
   bool InsertFormula(const Formula &F);
@@ -1083,6 +1090,9 @@ void LSRUse::print(raw_ostream &OS) const {
 
   if (AllFixupsOutsideLoop)
     OS << ", all-fixups-outside-loop";
+
+  if (WidestFixupType)
+    OS << ", widest fixup type: " << *WidestFixupType;
 }
 
 void LSRUse::dump() const {
@@ -1928,6 +1938,7 @@ LSRInstance::FindUseWithSimilarFormula(const Formula &OrigF,
     if (&LU != &OrigLU &&
         LU.Kind != LSRUse::ICmpZero &&
         LU.Kind == OrigLU.Kind && OrigLU.AccessTy == LU.AccessTy &&
+        LU.WidestFixupType == OrigLU.WidestFixupType &&
         LU.HasFormulaWithSameRegs(OrigF)) {
       for (SmallVectorImpl<Formula>::const_iterator I = LU.Formulae.begin(),
            E = LU.Formulae.end(); I != E; ++I) {
@@ -2066,6 +2077,10 @@ void LSRInstance::CollectFixupsAndInitialFormulae() {
     LF.Offset = P.second;
     LSRUse &LU = Uses[LF.LUIdx];
     LU.AllFixupsOutsideLoop &= LF.isUseFullyOutsideLoop(L);
+    if (!LU.WidestFixupType ||
+        SE.getTypeSizeInBits(LU.WidestFixupType) <
+        SE.getTypeSizeInBits(LF.OperandValToReplace->getType()))
+      LU.WidestFixupType = LF.OperandValToReplace->getType();
 
     // If this is the first use of this LSRUse, give it a formula.
     if (LU.Formulae.empty()) {
@@ -2195,6 +2210,10 @@ LSRInstance::CollectLoopInvariantFixupsAndFormulae() {
         LF.Offset = P.second;
         LSRUse &LU = Uses[LF.LUIdx];
         LU.AllFixupsOutsideLoop &= LF.isUseFullyOutsideLoop(L);
+        if (!LU.WidestFixupType ||
+            SE.getTypeSizeInBits(LU.WidestFixupType) <
+            SE.getTypeSizeInBits(LF.OperandValToReplace->getType()))
+          LU.WidestFixupType = LF.OperandValToReplace->getType();
         InsertSupplementalFormula(U, LU, LF.LUIdx);
         CountRegisters(LU.Formulae.back(), Uses.size() - 1);
         break;