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author | Chris Lattner <sabre@nondot.org> | 2010-09-05 02:18:34 +0000 |
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committer | Chris Lattner <sabre@nondot.org> | 2010-09-05 02:18:34 +0000 |
commit | beac75da3784929aee9f0357fc5cd76d49d6c3d7 (patch) | |
tree | 54525601bcdb388c49b9d014c90e6cbe8dbc1467 /lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp | |
parent | 07c2b7ff685523458f92339facfd814689e55873 (diff) | |
download | external_llvm-beac75da3784929aee9f0357fc5cd76d49d6c3d7.zip external_llvm-beac75da3784929aee9f0357fc5cd76d49d6c3d7.tar.gz external_llvm-beac75da3784929aee9f0357fc5cd76d49d6c3d7.tar.bz2 |
implement rdar://6653118 - fastisel should fold loads where possible.
Since mem2reg isn't run at -O0, we get a ton of reloads from the stack,
for example, before, this code:
int foo(int x, int y, int z) {
return x+y+z;
}
used to compile into:
_foo: ## @foo
subq $12, %rsp
movl %edi, 8(%rsp)
movl %esi, 4(%rsp)
movl %edx, (%rsp)
movl 8(%rsp), %edx
movl 4(%rsp), %esi
addl %edx, %esi
movl (%rsp), %edx
addl %esi, %edx
movl %edx, %eax
addq $12, %rsp
ret
Now we produce:
_foo: ## @foo
subq $12, %rsp
movl %edi, 8(%rsp)
movl %esi, 4(%rsp)
movl %edx, (%rsp)
movl 8(%rsp), %edx
addl 4(%rsp), %edx ## Folded load
addl (%rsp), %edx ## Folded load
movl %edx, %eax
addq $12, %rsp
ret
Fewer instructions and less register use = faster compiles.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@113102 91177308-0d34-0410-b5e6-96231b3b80d8
Diffstat (limited to 'lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp')
-rw-r--r-- | lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp | 52 |
1 files changed, 51 insertions, 1 deletions
diff --git a/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp b/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp index 66cb5ce..dead5d5 100644 --- a/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp +++ b/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp @@ -661,6 +661,43 @@ void SelectionDAGISel::PrepareEHLandingPad() { } } + + + +bool SelectionDAGISel::TryToFoldFastISelLoad(const LoadInst *LI, + FastISel *FastIS) { + // Don't try to fold volatile loads. Target has to deal with alignment + // constraints. + if (LI->isVolatile()) return false; + + // Figure out which vreg this is going into. + unsigned LoadReg = FastIS->getRegForValue(LI); + assert(LoadReg && "Load isn't already assigned a vreg? "); + + // Check to see what the uses of this vreg are. If it has no uses, or more + // than one use (at the machine instr level) then we can't fold it. + MachineRegisterInfo::reg_iterator RI = RegInfo->reg_begin(LoadReg); + if (RI == RegInfo->reg_end()) + return false; + + // See if there is exactly one use of the vreg. If there are multiple uses, + // then the instruction got lowered to multiple machine instructions or the + // use of the loaded value ended up being multiple operands of the result, in + // either case, we can't fold this. + MachineRegisterInfo::reg_iterator PostRI = RI; ++PostRI; + if (PostRI != RegInfo->reg_end()) + return false; + + assert(RI.getOperand().isUse() && + "The only use of the vreg must be a use, we haven't emitted the def!"); + + // Ask the target to try folding the load. + return FastIS->TryToFoldLoad(&*RI, RI.getOperandNo(), LI); +} + + + + void SelectionDAGISel::SelectAllBasicBlocks(const Function &Fn) { // Initialize the Fast-ISel state, if needed. FastISel *FastIS = 0; @@ -723,8 +760,21 @@ void SelectionDAGISel::SelectAllBasicBlocks(const Function &Fn) { FastIS->recomputeInsertPt(); // Try to select the instruction with FastISel. - if (FastIS->SelectInstruction(Inst)) + if (FastIS->SelectInstruction(Inst)) { + // If fast isel succeeded, check to see if there is a single-use + // non-volatile load right before the selected instruction, and see if + // the load is used by the instruction. If so, try to fold it. + const Instruction *BeforeInst = 0; + if (Inst != Begin) + BeforeInst = llvm::prior(llvm::prior(BI)); + if (BeforeInst && isa<LoadInst>(BeforeInst) && + BeforeInst->hasOneUse() && *BeforeInst->use_begin() == Inst && + TryToFoldFastISelLoad(cast<LoadInst>(BeforeInst), FastIS)) { + // If we succeeded, don't re-select the load. + --BI; + } continue; + } // Then handle certain instructions as single-LLVM-Instruction blocks. if (isa<CallInst>(Inst)) { |