From a9db12973005881a1bd1c5eddc31001d9c3189c8 Mon Sep 17 00:00:00 2001
From: Dan Gohman <gohman@apple.com>
Date: Thu, 15 Jul 2010 20:24:58 +0000
Subject: [PATCH] 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.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@108455 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Transforms/Scalar/LoopStrengthReduce.cpp | 21 +++++++++++++++++++-
 1 file changed, 20 insertions(+), 1 deletion(-)

diff --git a/lib/Transforms/Scalar/LoopStrengthReduce.cpp b/lib/Transforms/Scalar/LoopStrengthReduce.cpp
index 1612d895f21..adaadb26e9b 100644
--- a/lib/Transforms/Scalar/LoopStrengthReduce.cpp
+++ b/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;