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Bypass Slow Divides

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* 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
This commit is contained in:
Preston Gurd 2013-03-04 18:13:57 +00:00
parent ff4faabd2d
commit 9a2cfffdb6
5 changed files with 55 additions and 6 deletions
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7
lib/Target/X86/X86ISelLowering.cpp
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@ -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.

2
lib/Transforms/Scalar/CodeGenPrepare.cpp
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@ -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++)

4
lib/Transforms/Utils/BypassSlowDivision.cpp
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@ -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);

46
test/CodeGen/X86/atom-bypass-slow-division-64.ll Normal file
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@ -0,0 +1,46 @@
; RUN: llc < %s -mcpu=atom -mtriple=i686-linux -march=x86-64 | FileCheck %s
; Additional tests for 64-bit divide bypass
define i64 @Test_get_quotient(i64 %a, i64 %b) nounwind {
; CHECK: Test_get_quotient:
; CHECK: orq %rsi, %rcx
; CHECK-NEXT: testq $-65536, %rcx
; CHECK-NEXT: je
; CHECK: idivq
; CHECK: ret
; CHECK: divw
; CHECK: ret
%result = sdiv i64 %a, %b
ret i64 %result
}
define i64 @Test_get_remainder(i64 %a, i64 %b) nounwind {
; CHECK: Test_get_remainder:
; CHECK: orq %rsi, %rcx
; CHECK-NEXT: testq $-65536, %rcx
; CHECK-NEXT: je
; CHECK: idivq
; CHECK: ret
; CHECK: divw
; CHECK: ret
%result = srem i64 %a, %b
ret i64 %result
}
define i64 @Test_get_quotient_and_remainder(i64 %a, i64 %b) nounwind {
; CHECK: Test_get_quotient_and_remainder:
; CHECK: orq %rsi, %rcx
; CHECK-NEXT: testq $-65536, %rcx
; CHECK-NEXT: je
; CHECK: idivq
; CHECK: divw
; CHECK: addq
; CHECK: ret
; CHECK-NOT: idivq
; CHECK-NOT: divw
%resultdiv = sdiv i64 %a, %b
%resultrem = srem i64 %a, %b
%result = add i64 %resultdiv, %resultrem
ret i64 %result
}

2
test/CodeGen/X86/atom-bypass-slow-division.ll
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@ -1,4 +1,4 @@
; RUN: llc < %s -mcpu=atom -mtriple=i686-linux | FileCheck %s
; RUN: llc < %s -mcpu=atom -mtriple=i686-linux | FileCheck %s
define i32 @Test_get_quotient(i32 %a, i32 %b) nounwind {
; CHECK: Test_get_quotient: