[llvm] r251492 - [IndVarSimplify] Rewrite loop exit values with their initial values from loop preheader
Chen Li via llvm-commits
llvm-commits at lists.llvm.org
Tue Oct 27 23:02:41 PDT 2015
Yes, I think the issue is the next line:
+ if (isa<Instruction>(Cond) && !L->isLoopInvariant(Cond))
where isa<Instruction> takes a nullptr. I should have added a check after the if-elseif:
if (!Cond) continue;
or added an
else continue;
I think this should solve the problem, but I do want to run though some tests that the bots use to double check.
thanks,
chen
> On Oct 27, 2015, at 10:56 PM, Sanjoy Das <sanjoy at playingwithpointers.com> wrote:
>
> Looks like the bot is just building clang and running clang's test suite.
>
> But I think I've spotted what the bug is:
>
> Value *Cond = nullptr;
> if (auto *BI = dyn_cast<BranchInst>(TermInst)) {
> // Must be a conditional branch, otherwise the block
> // should not be in the loop.
> Cond = BI->getCondition();
> } else if (auto *SI = dyn_cast<SwitchInst>(TermInst)) {
> Cond = SI->getCondition();
> }
>
>
> ^^ you're missing an 'else' case here.
>
> -- Sanjoy
>
>
> Chen Li wrote:
>> I will revert it for now and investigate it. Is there an easy way to rerun the failed test case?
>>
>> thanks,
>> chen
>>
>>
>>> On Oct 27, 2015, at 10:08 PM, Sanjoy Das <sanjoy at playingwithpointers.com <mailto:sanjoy at playingwithpointers.com>> wrote:
>>>
>>> Looks like this broke some bots
>>> http://lab.llvm.org:8011/builders/clang-cmake-mips/builds/10258/steps/ninja%20check%201/logs/stdio
>>> <http://lab.llvm.org:8011/builders/clang-cmake-mips/builds/10258/steps/ninja check 1/logs/stdio>
>>>
>>> Sent from a mobile device, please excuse typos.
>>>
>>> On Oct 27, 2015 21:47, "Chen Li via llvm-commits" <llvm-commits at lists.llvm.org <mailto:llvm-commits at lists.llvm.org>>
>>> wrote:
>>>
>>> Author: chenli
>>> Date: Tue Oct 27 23:45:47 2015
>>> New Revision: 251492
>>>
>>> URL: http://llvm.org/viewvc/llvm-project?rev=251492&view=rev <http://llvm.org/viewvc/llvm-project?rev=251492&view=rev>
>>> Log:
>>> [IndVarSimplify] Rewrite loop exit values with their initial values from loop preheader
>>>
>>> Summary:
>>> This patch adds support to check if a loop has loop invariant conditions which lead to loop exits. If so, we know
>>> that if the exit path is taken, it is at the first loop iteration. If there is an induction variable used in that
>>> exit path whose value has not been updated, it will keep its initial value passing from loop preheader. We can
>>> therefore rewrite the exit value with
>>> its initial value. This will help remove phis created by LCSSA and enable other optimizations like loop unswitch.
>>>
>>>
>>> Reviewers: sanjoy
>>>
>>> Subscribers: llvm-commits
>>>
>>> Differential Revision: http://reviews.llvm.org/D13974
>>>
>>> Added:
>>> llvm/trunk/test/Transforms/IndVarSimplify/rewrite-loop-exit-value.ll
>>> Modified:
>>> llvm/trunk/lib/Transforms/Scalar/IndVarSimplify.cpp
>>> llvm/trunk/test/Transforms/LoopUnroll/scevunroll.ll
>>>
>>> Modified: llvm/trunk/lib/Transforms/Scalar/IndVarSimplify.cpp
>>> URL:
>>> http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/IndVarSimplify.cpp?rev=251492&r1=251491&r2=251492&view=diff
>>> <http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/IndVarSimplify.cpp?rev=251492&r1=251491&r2=251492&view=diff>
>>> ==============================================================================
>>> --- llvm/trunk/lib/Transforms/Scalar/IndVarSimplify.cpp (original)
>>> +++ llvm/trunk/lib/Transforms/Scalar/IndVarSimplify.cpp Tue Oct 27 23:45:47 2015
>>> @@ -132,6 +132,7 @@ private:
>>>
>>> bool canLoopBeDeleted(Loop *L, SmallVector<RewritePhi, 8> &RewritePhiSet);
>>> void rewriteLoopExitValues(Loop *L, SCEVExpander &Rewriter);
>>> + void rewriteFirstIterationLoopExitValues(Loop *L);
>>>
>>> Value *linearFunctionTestReplace(Loop *L, const SCEV *BackedgeTakenCount,
>>> PHINode *IndVar, SCEVExpander &Rewriter);
>>> @@ -700,6 +701,71 @@ void IndVarSimplify::rewriteLoopExitValu
>>> Rewriter.clearInsertPoint();
>>> }
>>>
>>> +//===---------------------------------------------------------------------===//
>>> +// rewriteFirstIterationLoopExitValues: Rewrite loop exit values if we know
>>> +// they will exit at the first iteration.
>>> +//===---------------------------------------------------------------------===//
>>> +
>>> +/// Check to see if this loop has loop invariant conditions which lead to loop
>>> +/// exits. If so, we know that if the exit path is taken, it is at the first
>>> +/// loop iteration. This lets us predict exit values of PHI nodes that live in
>>> +/// loop header.
>>> +void IndVarSimplify::rewriteFirstIterationLoopExitValues(Loop *L) {
>>> + // Verify the input to the pass is already in LCSSA form.
>>> + assert(L->isLCSSAForm(*DT));
>>> +
>>> + SmallVector<BasicBlock *, 8> ExitBlocks;
>>> + L->getUniqueExitBlocks(ExitBlocks);
>>> +
>>> + for (auto *ExitBB : ExitBlocks) {
>>> + BasicBlock::iterator begin = ExitBB->begin();
>>> + // If there are no more PHI nodes in this exit block, then no more
>>> + // values defined inside the loop are used on this path.
>>> + while (auto *PN = dyn_cast<PHINode>(begin++)) {
>>> + for (unsigned IncomingValIdx = 0, e = PN->getNumIncomingValues();
>>> + IncomingValIdx != e; ++IncomingValIdx) {
>>> + auto *IncomingBB = PN->getIncomingBlock(IncomingValIdx);
>>> + if (!L->contains(IncomingBB))
>>> + continue;
>>> +
>>> + // Get condition that leads to the exit path.
>>> + auto *TermInst = IncomingBB->getTerminator();
>>> +
>>> + Value *Cond = nullptr;
>>> + if (auto *BI = dyn_cast<BranchInst>(TermInst)) {
>>> + // Must be a conditional branch, otherwise the block
>>> + // should not be in the loop.
>>> + Cond = BI->getCondition();
>>> + } else if (auto *SI = dyn_cast<SwitchInst>(TermInst))
>>> + Cond = SI->getCondition();
>>> +
>>> + // All non-instructions are loop-invariant.
>>> + if (isa<Instruction>(Cond) && !L->isLoopInvariant(Cond))
>>> + continue;
>>> +
>>> + auto *ExitVal =
>>> + dyn_cast<PHINode>(PN->getIncomingValue(IncomingValIdx));
>>> +
>>> + // Only deal with PHIs.
>>> + if (!ExitVal)
>>> + continue;
>>> +
>>> + // If ExitVal is a PHI on the loop header, then we know its
>>> + // value along this exit because the exit can only be taken
>>> + // on the first iteration.
>>> + auto *LoopPreheader = L->getLoopPreheader();
>>> + assert(LoopPreheader && "Invalid loop");
>>> + if (ExitVal->getBasicBlockIndex(LoopPreheader) != -1) {
>>> + assert(ExitVal->getParent() == L->getHeader() &&
>>> + "ExitVal must be in loop header");
>>> + PN->setIncomingValue(IncomingValIdx,
>>> + ExitVal->getIncomingValueForBlock(LoopPreheader));
>>> + }
>>> + }
>>> + }
>>> + }
>>> +}
>>> +
>>> /// Check whether it is possible to delete the loop after rewriting exit
>>> /// value. If it is possible, ignore ReplaceExitValue and do rewriting
>>> /// aggressively.
>>> @@ -2173,6 +2239,11 @@ bool IndVarSimplify::runOnLoop(Loop *L,
>>> // loop may be sunk below the loop to reduce register pressure.
>>> sinkUnusedInvariants(L);
>>>
>>> + // rewriteFirstIterationLoopExitValues does not rely on the computation of
>>> + // trip count and therefore can further simplify exit values in addition to
>>> + // rewriteLoopExitValues.
>>> + rewriteFirstIterationLoopExitValues(L);
>>> +
>>> // Clean up dead instructions.
>>> Changed |= DeleteDeadPHIs(L->getHeader(), TLI);
>>> // Check a post-condition.
>>>
>>> Added: llvm/trunk/test/Transforms/IndVarSimplify/rewrite-loop-exit-value.ll
>>> URL:
>>> http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/IndVarSimplify/rewrite-loop-exit-value.ll?rev=251492&view=auto
>>> <http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/IndVarSimplify/rewrite-loop-exit-value.ll?rev=251492&view=auto>
>>> ==============================================================================
>>> --- llvm/trunk/test/Transforms/IndVarSimplify/rewrite-loop-exit-value.ll (added)
>>> +++ llvm/trunk/test/Transforms/IndVarSimplify/rewrite-loop-exit-value.ll Tue Oct 27 23:45:47 2015
>>> @@ -0,0 +1,75 @@
>>> +; RUN: opt -indvars -instcombine -S < %s | FileCheck %s
>>> +
>>> +;; Test that loop's exit value is rewritten to its initial
>>> +;; value from loop preheader
>>> +define i32 @test1(i32* %var) {
>>> +; CHECK-LABEL: @test1
>>> +entry:
>>> + %cond = icmp eq i32* %var, null
>>> + br label %header
>>> +
>>> +header:
>>> + %phi_indvar = phi i32 [0, %entry], [%indvar, %loop]
>>> + br i1 %cond, label %loop, label %exit
>>> +
>>> +loop:
>>> + %indvar = add i32 %phi_indvar, 1
>>> + br label %header
>>> +
>>> +exit:
>>> +; CHECK: ret i32 0
>>> + ret i32 %phi_indvar
>>> +}
>>> +
>>> +
>>> +;; Test that inner loop's exit value is first rewritten to outer
>>> +;; loop's induction variable, and then further rewritten to a
>>> +;; constant when process outer loop.
>>> +define i32 @test2(i32* %var1, i32* %var2) {
>>> +; CHECK-LABEL: @test2
>>> +entry:
>>> + %cond1 = icmp eq i32* %var1, null
>>> + %cond2 = icmp eq i32* %var2, null
>>> + br label %outer_header
>>> +
>>> +outer_header:
>>> + %phi_outer = phi i32 [0, %entry], [%indvar_outer, %inner_exit]
>>> + br label %inner_header
>>> +
>>> +inner_header:
>>> + %phi_inner = phi i32 [%phi_outer, %outer_header], [%indvar_inner, %loop]
>>> + br i1 %cond1, label %loop, label %exit
>>> +
>>> +loop:
>>> + %indvar_inner = add i32 %phi_inner, 1
>>> + br i1 %cond2, label %inner_header, label %inner_exit
>>> +
>>> +inner_exit:
>>> + %indvar_outer = add i32 %phi_outer, 1
>>> + br label %outer_header
>>> +
>>> +exit:
>>> +;; %phi_inner is first rewritten to %phi_outer
>>> +;; and then %phi_outer is rewritten to 0
>>> + %ret_val = add i32 %phi_inner, %phi_outer
>>> +; CHECK: ret i32 0
>>> + ret i32 %ret_val
>>> +}
>>> +
>>> +;; Test that we can not rewrite loop exit value if it's not
>>> +;; a phi node (%indvar is an add instruction in this test).
>>> +define i32 @test3(i32* %var) {
>>> +; CHECK-LABEL: @test3
>>> +entry:
>>> + %cond = icmp eq i32* %var, null
>>> + br label %header
>>> +
>>> +header:
>>> + %phi_indvar = phi i32 [0, %entry], [%indvar, %header]
>>> + %indvar = add i32 %phi_indvar, 1
>>> + br i1 %cond, label %header, label %exit
>>> +
>>> +exit:
>>> +; CHECK: ret i32 %indvar
>>> + ret i32 %indvar
>>> +}
>>> \ No newline at end of file
>>>
>>> Modified: llvm/trunk/test/Transforms/LoopUnroll/scevunroll.ll
>>> URL:
>>> http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/LoopUnroll/scevunroll.ll?rev=251492&r1=251491&r2=251492&view=diff
>>> <http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/LoopUnroll/scevunroll.ll?rev=251492&r1=251491&r2=251492&view=diff>
>>> ==============================================================================
>>> --- llvm/trunk/test/Transforms/LoopUnroll/scevunroll.ll (original)
>>> +++ llvm/trunk/test/Transforms/LoopUnroll/scevunroll.ll Tue Oct 27 23:45:47 2015
>>> @@ -184,7 +184,7 @@ for.body87:
>>> ; CHECK: for.body:
>>> ; CHECK: %b.03 = phi i32 [ 0, %entry ], [ %add, %for.cond ]
>>> ; CHECK: return:
>>> -; CHECK: %b.03.lcssa = phi i32 [ %b.03, %for.body ], [ %b.03, %for.cond ]
>>> +; CHECK: %b.03.lcssa = phi i32 [ %b.03, %for.body ], [ 0, %for.cond ]
>>> define void @nsw_latch(i32* %a) nounwind {
>>> entry:
>>> br label %for.body
>>>
>>>
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