[llvm-commits] [llvm] r134695 - in /llvm/trunk: include/llvm/Target/TargetLowering.h lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp lib/CodeGen/SelectionDAG/SelectionDAGBuilder.h lib/CodeGen/SelectionDAG/TargetLowering.cpp test/CodeGen/X86/sdiv-exact.ll
Benjamin Kramer
benny.kra at googlemail.com
Fri Jul 8 03:31:31 PDT 2011
Author: d0k
Date: Fri Jul 8 05:31:30 2011
New Revision: 134695
URL: http://llvm.org/viewvc/llvm-project?rev=134695&view=rev
Log:
Emit a more efficient magic number multiplication for exact sdivs.
We have to do this in DAGBuilder instead of DAGCombiner, because the exact bit is lost after building.
struct foo { char x[24]; };
long bar(struct foo *a, struct foo *b) { return a-b; }
is now compiled into
movl 4(%esp), %eax
subl 8(%esp), %eax
sarl $3, %eax
imull $-1431655765, %eax, %eax
instead of
movl 4(%esp), %eax
subl 8(%esp), %eax
movl $715827883, %ecx
imull %ecx
movl %edx, %eax
shrl $31, %eax
sarl $2, %edx
addl %eax, %edx
movl %edx, %eax
Added:
llvm/trunk/test/CodeGen/X86/sdiv-exact.ll
Modified:
llvm/trunk/include/llvm/Target/TargetLowering.h
llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.h
llvm/trunk/lib/CodeGen/SelectionDAG/TargetLowering.cpp
Modified: llvm/trunk/include/llvm/Target/TargetLowering.h
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/Target/TargetLowering.h?rev=134695&r1=134694&r2=134695&view=diff
==============================================================================
--- llvm/trunk/include/llvm/Target/TargetLowering.h (original)
+++ llvm/trunk/include/llvm/Target/TargetLowering.h Fri Jul 8 05:31:30 2011
@@ -1540,6 +1540,8 @@
//===--------------------------------------------------------------------===//
// Div utility functions
//
+ SDValue BuildExactSDIV(SDValue Op1, SDValue Op2, DebugLoc dl,
+ SelectionDAG &DAG) const;
SDValue BuildSDIV(SDNode *N, SelectionDAG &DAG,
std::vector<SDNode*>* Created) const;
SDValue BuildUDIV(SDNode *N, SelectionDAG &DAG,
Modified: llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp?rev=134695&r1=134694&r2=134695&view=diff
==============================================================================
--- llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp (original)
+++ llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp Fri Jul 8 05:31:30 2011
@@ -2501,6 +2501,22 @@
Op1.getValueType(), Op1, Op2));
}
+void SelectionDAGBuilder::visitSDiv(const User &I) {
+ const BinaryOperator *BO = cast<BinaryOperator>(&I);
+ SDValue Op1 = getValue(I.getOperand(0));
+ SDValue Op2 = getValue(I.getOperand(1));
+
+ // Turn exact SDivs into multiplications.
+ // FIXME: This should be in DAGCombiner, but it doesn't have access to the
+ // exact bit.
+ if (BO->isExact() && !isa<ConstantSDNode>(Op1) &&
+ isa<ConstantSDNode>(Op2) && !cast<ConstantSDNode>(Op2)->isNullValue())
+ setValue(&I, TLI.BuildExactSDIV(Op1, Op2, getCurDebugLoc(), DAG));
+ else
+ setValue(&I, DAG.getNode(ISD::SDIV, getCurDebugLoc(), Op1.getValueType(),
+ Op1, Op2));
+}
+
void SelectionDAGBuilder::visitICmp(const User &I) {
ICmpInst::Predicate predicate = ICmpInst::BAD_ICMP_PREDICATE;
if (const ICmpInst *IC = dyn_cast<ICmpInst>(&I))
Modified: llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.h
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.h?rev=134695&r1=134694&r2=134695&view=diff
==============================================================================
--- llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.h (original)
+++ llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.h Fri Jul 8 05:31:30 2011
@@ -467,7 +467,7 @@
void visitSRem(const User &I) { visitBinary(I, ISD::SREM); }
void visitFRem(const User &I) { visitBinary(I, ISD::FREM); }
void visitUDiv(const User &I) { visitBinary(I, ISD::UDIV); }
- void visitSDiv(const User &I) { visitBinary(I, ISD::SDIV); }
+ void visitSDiv(const User &I);
void visitFDiv(const User &I) { visitBinary(I, ISD::FDIV); }
void visitAnd (const User &I) { visitBinary(I, ISD::AND); }
void visitOr (const User &I) { visitBinary(I, ISD::OR); }
Modified: llvm/trunk/lib/CodeGen/SelectionDAG/TargetLowering.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/SelectionDAG/TargetLowering.cpp?rev=134695&r1=134694&r2=134695&view=diff
==============================================================================
--- llvm/trunk/lib/CodeGen/SelectionDAG/TargetLowering.cpp (original)
+++ llvm/trunk/lib/CodeGen/SelectionDAG/TargetLowering.cpp Fri Jul 8 05:31:30 2011
@@ -3211,6 +3211,32 @@
return true;
}
+/// BuildExactDiv - Given an exact SDIV by a constant, create a multiplication
+/// with the multiplicative inverse of the constant.
+SDValue TargetLowering::BuildExactSDIV(SDValue Op1, SDValue Op2, DebugLoc dl,
+ SelectionDAG &DAG) const {
+ ConstantSDNode *C = cast<ConstantSDNode>(Op2);
+ APInt d = C->getAPIntValue();
+ assert(d != 0 && "Division by zero!");
+
+ // Shift the value upfront if it is even, so the LSB is one.
+ unsigned ShAmt = d.countTrailingZeros();
+ if (ShAmt) {
+ // TODO: For UDIV use SRL instead of SRA.
+ SDValue Amt = DAG.getConstant(ShAmt, getShiftAmountTy(Op1.getValueType()));
+ Op1 = DAG.getNode(ISD::SRA, dl, Op1.getValueType(), Op1, Amt);
+ d = d.ashr(ShAmt);
+ }
+
+ // Calculate the multiplicative inverse, using Newton's method.
+ APInt t, xn = d;
+ while ((t = d*xn) != 1)
+ xn *= APInt(d.getBitWidth(), 2) - t;
+
+ Op2 = DAG.getConstant(xn, Op1.getValueType());
+ return DAG.getNode(ISD::MUL, dl, Op1.getValueType(), Op1, Op2);
+}
+
/// BuildSDIVSequence - Given an ISD::SDIV node expressing a divide by constant,
/// return a DAG expression to select that will generate the same value by
/// multiplying by a magic number. See:
Added: llvm/trunk/test/CodeGen/X86/sdiv-exact.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/X86/sdiv-exact.ll?rev=134695&view=auto
==============================================================================
--- llvm/trunk/test/CodeGen/X86/sdiv-exact.ll (added)
+++ llvm/trunk/test/CodeGen/X86/sdiv-exact.ll Fri Jul 8 05:31:30 2011
@@ -0,0 +1,18 @@
+; RUN: llc -march=x86 < %s | FileCheck %s
+
+define i32 @test1(i32 %x) {
+ %div = sdiv exact i32 %x, 25
+ ret i32 %div
+; CHECK: test1:
+; CHECK: imull $-1030792151, 4(%esp)
+; CHECK-NEXT: ret
+}
+
+define i32 @test2(i32 %x) {
+ %div = sdiv exact i32 %x, 24
+ ret i32 %div
+; CHECK: test2:
+; CHECK: sarl $3
+; CHECK-NEXT: imull $-1431655765
+; CHECK-NEXT: ret
+}
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