[llvm-commits] [llvm] r107380 - in /llvm/trunk: include/llvm/CodeGen/FastISel.h lib/CodeGen/SelectionDAG/FastISel.cpp test/CodeGen/X86/fast-isel-loads.ll
Dan Gohman
gohman at apple.com
Wed Jun 30 20:49:38 PDT 2010
Author: djg
Date: Wed Jun 30 22:49:38 2010
New Revision: 107380
URL: http://llvm.org/viewvc/llvm-project?rev=107380&view=rev
Log:
Teach fast-isel to avoid loading a value from memory when it's already
available in a register. This is pretty primitive, but it reduces the
number of instructions in common testcases by 4%.
Added:
llvm/trunk/test/CodeGen/X86/fast-isel-loads.ll
Modified:
llvm/trunk/include/llvm/CodeGen/FastISel.h
llvm/trunk/lib/CodeGen/SelectionDAG/FastISel.cpp
Modified: llvm/trunk/include/llvm/CodeGen/FastISel.h
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/CodeGen/FastISel.h?rev=107380&r1=107379&r2=107380&view=diff
==============================================================================
--- llvm/trunk/include/llvm/CodeGen/FastISel.h (original)
+++ llvm/trunk/include/llvm/CodeGen/FastISel.h Wed Jun 30 22:49:38 2010
@@ -307,6 +307,8 @@
}
private:
+ bool SelectLoad(const User *I);
+
bool SelectBinaryOp(const User *I, unsigned ISDOpcode);
bool SelectFNeg(const User *I);
Modified: llvm/trunk/lib/CodeGen/SelectionDAG/FastISel.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/SelectionDAG/FastISel.cpp?rev=107380&r1=107379&r2=107380&view=diff
==============================================================================
--- llvm/trunk/lib/CodeGen/SelectionDAG/FastISel.cpp (original)
+++ llvm/trunk/lib/CodeGen/SelectionDAG/FastISel.cpp Wed Jun 30 22:49:38 2010
@@ -48,6 +48,7 @@
#include "llvm/CodeGen/MachineModuleInfo.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/Analysis/DebugInfo.h"
+#include "llvm/Analysis/Loads.h"
#include "llvm/Target/TargetData.h"
#include "llvm/Target/TargetInstrInfo.h"
#include "llvm/Target/TargetLowering.h"
@@ -716,8 +717,31 @@
}
bool
+FastISel::SelectLoad(const User *I) {
+ LoadInst *LI = const_cast<LoadInst *>(cast<LoadInst>(I));
+
+ // For a load from an alloca, make a limited effort to find the value
+ // already available in a register, avoiding redundant loads.
+ if (!LI->isVolatile() && isa<AllocaInst>(LI->getPointerOperand())) {
+ BasicBlock::iterator ScanFrom = LI;
+ if (const Value *V = FindAvailableLoadedValue(LI->getPointerOperand(),
+ LI->getParent(), ScanFrom)) {
+ unsigned ResultReg = getRegForValue(V);
+ if (ResultReg != 0) {
+ UpdateValueMap(I, ResultReg);
+ return true;
+ }
+ }
+ }
+
+ return false;
+}
+
+bool
FastISel::SelectOperator(const User *I, unsigned Opcode) {
switch (Opcode) {
+ case Instruction::Load:
+ return SelectLoad(I);
case Instruction::Add:
return SelectBinaryOp(I, ISD::ADD);
case Instruction::FAdd:
Added: llvm/trunk/test/CodeGen/X86/fast-isel-loads.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/X86/fast-isel-loads.ll?rev=107380&view=auto
==============================================================================
--- llvm/trunk/test/CodeGen/X86/fast-isel-loads.ll (added)
+++ llvm/trunk/test/CodeGen/X86/fast-isel-loads.ll Wed Jun 30 22:49:38 2010
@@ -0,0 +1,23 @@
+; RUN: llc -march=x86-64 -O0 -asm-verbose=false < %s | FileCheck %s
+
+; Fast-isel shouldn't reload the argument values from the stack.
+
+; CHECK: foo:
+; CHECK-NEXT: movq %rdi, -8(%rsp)
+; CHECK-NEXT: movq %rsi, -16(%rsp)
+; CHECK-NEXT: movsd 128(%rsi,%rdi,8), %xmm0
+; CHECK-NEXT: ret
+
+define double @foo(i64 %x, double* %p) nounwind {
+entry:
+ %x.addr = alloca i64, align 8 ; <i64*> [#uses=2]
+ %p.addr = alloca double*, align 8 ; <double**> [#uses=2]
+ store i64 %x, i64* %x.addr
+ store double* %p, double** %p.addr
+ %tmp = load i64* %x.addr ; <i64> [#uses=1]
+ %tmp1 = load double** %p.addr ; <double*> [#uses=1]
+ %add = add nsw i64 %tmp, 16 ; <i64> [#uses=1]
+ %arrayidx = getelementptr inbounds double* %tmp1, i64 %add ; <double*> [#uses=1]
+ %tmp2 = load double* %arrayidx ; <double> [#uses=1]
+ ret double %tmp2
+}
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