[llvm] r251492 - [IndVarSimplify] Rewrite loop exit values with their initial values from loop preheader
Sanjoy Das via llvm-commits
llvm-commits at lists.llvm.org
Tue Oct 27 22:56:38 PDT 2015
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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