Author: hans Date: Wed Aug 9 16:52:05 2017 New Revision: 310538 URL: http://llvm.org/viewvc/llvm-project?rev=310538&view=rev Log: Merging r309758: ------------------------------------------------------------------------ r309758 | sanjoy | 2017-08-01 15:37:58 -0700 (Tue, 01 Aug 2017) | 6 lines
[SCEV/IndVars] Always compute loop exiting values if the backedge count is 0 If SCEV can prove that the backedge taken count for a loop is zero, it does not need to "understand" a recursive PHI to compute its exiting value. This should fix PR33885. ------------------------------------------------------------------------ Modified: llvm/branches/release_50/ (props changed) llvm/branches/release_50/lib/Analysis/ScalarEvolution.cpp llvm/branches/release_50/test/Transforms/IndVarSimplify/exit_value_test2.ll Propchange: llvm/branches/release_50/ ------------------------------------------------------------------------------ --- svn:mergeinfo (original) +++ svn:mergeinfo Wed Aug 9 16:52:05 2017 @@ -1,3 +1,3 @@ /llvm/branches/Apple/Pertwee:110850,110961 /llvm/branches/type-system-rewrite:133420-134817 -/llvm/trunk:155241,308483-308484,308503,308808,308813,308891,308906,308950,308963,308978,308986,309113,309302,309321,309323,309325,309330,309343,309353,309355,309422,309481,309483,309495,309555,309561,309594,309651,309744,309849,309928,309930,310071,310190,310240-310242,310250,310253,310267 +/llvm/trunk:155241,308483-308484,308503,308808,308813,308891,308906,308950,308963,308978,308986,309113,309302,309321,309323,309325,309330,309343,309353,309355,309422,309481,309483,309495,309555,309561,309594,309651,309744,309758,309849,309928,309930,310071,310190,310240-310242,310250,310253,310267 Modified: llvm/branches/release_50/lib/Analysis/ScalarEvolution.cpp URL: http://llvm.org/viewvc/llvm-project/llvm/branches/release_50/lib/Analysis/ScalarEvolution.cpp?rev=310538&r1=310537&r2=310538&view=diff ============================================================================== --- llvm/branches/release_50/lib/Analysis/ScalarEvolution.cpp (original) +++ llvm/branches/release_50/lib/Analysis/ScalarEvolution.cpp Wed Aug 9 16:52:05 2017 @@ -7582,6 +7582,25 @@ const SCEV *ScalarEvolution::computeSCEV const SCEV *BackedgeTakenCount = getBackedgeTakenCount(LI); if (const SCEVConstant *BTCC = dyn_cast<SCEVConstant>(BackedgeTakenCount)) { + + // This trivial case can show up in some degenerate cases where + // the incoming IR has not yet been fully simplified. + if (BTCC->getValue()->isZero()) { + Value *InitValue = nullptr; + bool MultipleInitValues = false; + for (unsigned i = 0; i < PN->getNumIncomingValues(); i++) { + if (!LI->contains(PN->getIncomingBlock(i))) { + if (!InitValue) + InitValue = PN->getIncomingValue(i); + else if (InitValue != PN->getIncomingValue(i)) { + MultipleInitValues = true; + break; + } + } + if (!MultipleInitValues && InitValue) + return getSCEV(InitValue); + } + } // Okay, we know how many times the containing loop executes. If // this is a constant evolving PHI node, get the final value at // the specified iteration number. Modified: llvm/branches/release_50/test/Transforms/IndVarSimplify/exit_value_test2.ll URL: http://llvm.org/viewvc/llvm-project/llvm/branches/release_50/test/Transforms/IndVarSimplify/exit_value_test2.ll?rev=310538&r1=310537&r2=310538&view=diff ============================================================================== --- llvm/branches/release_50/test/Transforms/IndVarSimplify/exit_value_test2.ll (original) +++ llvm/branches/release_50/test/Transforms/IndVarSimplify/exit_value_test2.ll Wed Aug 9 16:52:05 2017 @@ -3,15 +3,14 @@ ; Check IndVarSimplify should not replace exit value because or else ; udiv will be introduced by expand and the cost will be high. -; -; CHECK-LABEL: @_Z3fooPKcjj( -; CHECK-NOT: udiv declare void @_Z3mixRjj(i32* dereferenceable(4), i32) declare void @llvm.lifetime.start.p0i8(i64, i8* nocapture) declare void @llvm.lifetime.end.p0i8(i64, i8* nocapture) define i32 @_Z3fooPKcjj(i8* nocapture readonly %s, i32 %len, i32 %c) { +; CHECK-LABEL: @_Z3fooPKcjj( +; CHECK-NOT: udiv entry: %a = alloca i32, align 4 %tmp = bitcast i32* %a to i8* @@ -50,3 +49,26 @@ while.end: call void @llvm.lifetime.end.p0i8(i64 4, i8* %tmp) ret i32 %tmp4 } + +define i32 @zero_backedge_count_test(i32 %unknown_init, i32* %unknown_mem) { +; CHECK-LABEL: @zero_backedge_count_test( +entry: + br label %loop + +loop: + %iv = phi i32 [ 0, %entry], [ %iv.inc, %loop ] + %unknown_phi = phi i32 [ %unknown_init, %entry ], [ %unknown_next, %loop ] + %iv.inc = add i32 %iv, 1 + %be_taken = icmp ne i32 %iv.inc, 1 + %unknown_next = load volatile i32, i32* %unknown_mem + br i1 %be_taken, label %loop, label %leave + +leave: +; We can fold %unknown_phi even though the backedge value for it is completely +; unknown, since we can prove that the loop's backedge taken count is 0. + +; CHECK: leave: +; CHECK: ret i32 %unknown_init + %exit_val = phi i32 [ %unknown_phi, %loop ] + ret i32 %exit_val +} _______________________________________________ llvm-branch-commits mailing list llvm-branch-commits@lists.llvm.org http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-branch-commits