Bypass Slow Divides

* Only apply divide bypass optimization when not optimizing for size. 
* Fixed bug caused by constant for 0 value of type Int32,
  used dividend type to generate the constant instead.
* For atom x86-64 apply the divide bypass to use 16-bit divides instead of
  64-bit divides when operand values are small enough.
* Added lit tests for 64-bit divide bypass.

Patch by Tyler Nowicki!




git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@176442 91177308-0d34-0410-b5e6-96231b3b80d8

3 files changed, 8 insertions, 5 deletions

diff --git a/lib/Target/X86/X86ISelLowering.cpp b/lib/Target/X86/X86ISelLowering.cpp
index 451acca..5d12b0a 100644
--- a/lib/Target/X86/X86ISelLowering.cpp
+++ b/lib/Target/X86/X86ISelLowering.cpp
@@ -181,9 +181,12 @@ X86TargetLowering::X86TargetLowering(X86TargetMachine &TM)
     setSchedulingPreference(Sched::RegPressure);
   setStackPointerRegisterToSaveRestore(RegInfo->getStackRegister());
 
-  // Bypass i32 with i8 on Atom when compiling with O2
-  if (Subtarget->hasSlowDivide() && TM.getOptLevel() >= CodeGenOpt::Default)
+  // Bypass expensive divides on Atom when compiling with O2
+  if (Subtarget->hasSlowDivide() && TM.getOptLevel() >= CodeGenOpt::Default) {
     addBypassSlowDiv(32, 8);
+    if (Subtarget->is64Bit())
+      addBypassSlowDiv(64, 16);
+  }
 
   if (Subtarget->isTargetWindows() && !Subtarget->isTargetCygMing()) {
     // Setup Windows compiler runtime calls.
diff --git a/lib/Transforms/Scalar/CodeGenPrepare.cpp b/lib/Transforms/Scalar/CodeGenPrepare.cpp
index d71dd5d..015fd2e 100644
--- a/lib/Transforms/Scalar/CodeGenPrepare.cpp
+++ b/lib/Transforms/Scalar/CodeGenPrepare.cpp
@@ -154,7 +154,7 @@ bool CodeGenPrepare::runOnFunction(Function &F) {
 
   /// This optimization identifies DIV instructions that can be
   /// profitably bypassed and carried out with a shorter, faster divide.
-  if (TLI && TLI->isSlowDivBypassed()) {
+  if (!OptSize && TLI && TLI->isSlowDivBypassed()) {
     const DenseMap<unsigned int, unsigned int> &BypassWidths =
        TLI->getBypassSlowDivWidths();
     for (Function::iterator I = F.begin(); I != F.end(); I++)
diff --git a/lib/Transforms/Utils/BypassSlowDivision.cpp b/lib/Transforms/Utils/BypassSlowDivision.cpp
index 00cda8e..1f517d0 100644
--- a/lib/Transforms/Utils/BypassSlowDivision.cpp
+++ b/lib/Transforms/Utils/BypassSlowDivision.cpp
@@ -163,7 +163,7 @@ static bool insertFastDiv(Function &F,
   Value *AndV = MainBuilder.CreateAnd(OrV, BitMask);
 
   // Compare operand values and branch
-  Value *ZeroV = MainBuilder.getInt32(0);
+  Value *ZeroV = ConstantInt::getSigned(Dividend->getType(), 0);
   Value *CmpV = MainBuilder.CreateICmpEQ(AndV, ZeroV);
   MainBuilder.CreateCondBr(CmpV, FastBB, SlowBB);
 
@@ -244,7 +244,7 @@ bool llvm::bypassSlowDivision(Function &F,
 
     // Get bitwidth of div/rem instruction
     IntegerType *T = cast<IntegerType>(J->getType());
-    int bitwidth = T->getBitWidth();
+    unsigned int bitwidth = T->getBitWidth();
 
     // Continue if bitwidth is not bypassed
     DenseMap<unsigned int, unsigned int>::const_iterator BI = BypassWidths.find(bitwidth);