Add support to indvars for optimizing sadd.with.overflow.

Split sadd.with.overflow into add + sadd.with.overflow to allow
analysis and optimization. This should ideally be done after
InstCombine, which can perform code motion (eventually indvars should
run after all canonical instcombines). We want ISEL to recombine the
add and the check, at least on x86.

This is currently under an option for reducing live induction
variables: -liv-reduce. The next step is reducing liveness of IVs that
are live out of the overflow check paths. Once the related
optimizations are fully developed, reviewed and tested, I do expect
this to become default.

llvm-svn: 197926

1 files changed, 11 insertions, 3 deletions

diff --git a/llvm/lib/Transforms/Scalar/IndVarSimplify.cpp b/llvm/lib/Transforms/Scalar/IndVarSimplify.cpp
index 235aaaa6f80..c291f68bd63 100644
--- a/llvm/lib/Transforms/Scalar/IndVarSimplify.cpp
+++ b/llvm/lib/Transforms/Scalar/IndVarSimplify.cpp
@@ -63,6 +63,9 @@ static cl::opt<bool> VerifyIndvars(
   "verify-indvars", cl::Hidden,
   cl::desc("Verify the ScalarEvolution result after running indvars"));
 
+static cl::opt<bool> ReduceLiveIVs("liv-reduce", cl::Hidden,
+  cl::desc("Reduce live induction variables."));
+
 namespace {
   class IndVarSimplify : public LoopPass {
     LoopInfo        *LI;
@@ -643,8 +646,11 @@ namespace {
     WideIVInfo WI;
 
     WideIVVisitor(PHINode *NarrowIV, ScalarEvolution *SCEV,
-                  const DataLayout *TData) :
-      SE(SCEV), TD(TData) { WI.NarrowIV = NarrowIV; }
+                  const DataLayout *TData, const DominatorTree *DTree):
+      SE(SCEV), TD(TData) {
+      DT = DTree;
+      WI.NarrowIV = NarrowIV;
+    }
 
     // Implement the interface used by simplifyUsersOfIV.
     virtual void visitCast(CastInst *Cast);
@@ -1114,7 +1120,9 @@ void IndVarSimplify::SimplifyAndExtend(Loop *L,
       PHINode *CurrIV = LoopPhis.pop_back_val();
 
       // Information about sign/zero extensions of CurrIV.
-      WideIVVisitor WIV(CurrIV, SE, TD);
+      WideIVVisitor WIV(CurrIV, SE, TD, DT);
+      if (ReduceLiveIVs)
+        WIV.setSplitOverflowIntrinsics();
 
       Changed |= simplifyUsersOfIV(CurrIV, SE, &LPM, DeadInsts, &WIV);