forked from OSchip/llvm-project
RegisterCoalescer: Prune undef subranges from copy pairs in loops
If we had a pair of copies inside a loop which introduced new liveness to a subregister which was undef before the loop, we would have a dummy phi-only segment remaining across the loop body. Later, this false segment would confuse RenameIndependentSubregs causing it to introduce IMPLICIT_DEFs with broken value numbering. It seems always adding the lanes to ShrinkMask is OK, so any conditions should be purely a compile time filter.
This commit is contained in:
Matt Arsenault
parent
5580fa10db
commit
d886da042c
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@ -3114,6 +3114,13 @@ void JoinVals::pruneValues(JoinVals &Other,
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}
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}
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// Check if the segment consists of a copied live-through value (i.e. the copy
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// in the block only extended the liveness, of an undef value which we may need
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// to handle).
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static bool isLiveThrough(const LiveQueryResult Q) {
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return Q.valueIn() && Q.valueIn()->isPHIDef() && Q.valueIn() == Q.valueOut();
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}
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/// Consider the following situation when coalescing the copy between
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/// %31 and %45 at 800. (The vertical lines represent live range segments.)
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///
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@ -3196,11 +3203,21 @@ void JoinVals::pruneSubRegValues(LiveInterval &LI, LaneBitmask &ShrinkMask) {
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// with V.OtherVNI.
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LIS->extendToIndices(S, EndPoints);
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}
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// We may need to eliminate the subrange if the copy introduced a live
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// out undef value.
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if (ValueOut->isPHIDef())
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ShrinkMask |= S.LaneMask;
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continue;
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}
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// If a subrange ends at the copy, then a value was copied but only
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// partially used later. Shrink the subregister range appropriately.
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if (Q.valueIn() != nullptr && Q.valueOut() == nullptr) {
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//
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// Ultimately this calls shrinkToUses, so assuming ShrinkMask is
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// conservatively correct.
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if ((Q.valueIn() != nullptr && Q.valueOut() == nullptr) ||
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(V.Resolution == CR_Erase && isLiveThrough(Q))) {
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LLVM_DEBUG(dbgs() << "\t\tDead uses at sublane "
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<< PrintLaneMask(S.LaneMask) << " at " << Def
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<< "\n");
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@ -250,57 +250,150 @@ body: |
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...
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# FIXME: This testcase is broken
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# The coalescing of the %0 = %2 COPY in %bb.2 needs to prune the dead
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# phi range across %bb.1 after it is erased.
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# ---
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# name: prune_subrange_phi_value_0
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# tracksRegLiveness: true
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# body: |
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# bb.0:
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# liveins: $vgpr0
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---
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name: prune_subrange_phi_value_0
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tracksRegLiveness: true
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body: |
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; CHECK-LABEL: name: prune_subrange_phi_value_0
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; CHECK: bb.0:
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; CHECK: successors: %bb.1(0x80000000)
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; CHECK: liveins: $vgpr0
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; CHECK: undef %2.sub1:vreg_64 = COPY $vgpr0
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; CHECK: bb.1:
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; CHECK: successors: %bb.2(0x40000000), %bb.1(0x40000000)
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; CHECK: S_CBRANCH_EXECNZ %bb.1, implicit $exec
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; CHECK: S_BRANCH %bb.2
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; CHECK: bb.2:
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; CHECK: successors: %bb.1(0x80000000)
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; CHECK: S_BRANCH %bb.1
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bb.0:
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liveins: $vgpr0
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# undef %0.sub1:vreg_64 = COPY killed $vgpr0
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undef %0.sub1:vreg_64 = COPY killed $vgpr0
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# bb.1:
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# successors: %bb.2, %bb.1
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bb.1:
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successors: %bb.2, %bb.1
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# %1:vreg_64 = COPY killed %0
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# %0:vreg_64 = COPY %1
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# S_CBRANCH_EXECNZ %bb.1, implicit $exec
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# S_BRANCH %bb.2
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%1:vreg_64 = COPY killed %0
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%0:vreg_64 = COPY %1
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S_CBRANCH_EXECNZ %bb.1, implicit $exec
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S_BRANCH %bb.2
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# bb.2:
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# undef %2.sub1:vreg_64 = COPY %0.sub1
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# %0:vreg_64 = COPY killed %2
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# S_BRANCH %bb.1
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bb.2:
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undef %2.sub1:vreg_64 = COPY %0.sub1
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%0:vreg_64 = COPY killed %2
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S_BRANCH %bb.1
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# ...
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...
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---
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name: prune_subrange_phi_value_0_0
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tracksRegLiveness: true
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body: |
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; CHECK-LABEL: name: prune_subrange_phi_value_0_0
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; CHECK: bb.0:
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; CHECK: successors: %bb.1(0x80000000)
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; CHECK: liveins: $vgpr0
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; CHECK: undef %0.sub1:vreg_64 = COPY $vgpr0
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; CHECK: bb.1:
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; CHECK: successors: %bb.2(0x40000000), %bb.1(0x40000000)
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; CHECK: S_CBRANCH_EXECNZ %bb.1, implicit $exec
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; CHECK: S_BRANCH %bb.2
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; CHECK: bb.2:
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; CHECK: successors: %bb.1(0x80000000)
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; CHECK: S_BRANCH %bb.1
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bb.0:
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liveins: $vgpr0
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undef %0.sub1:vreg_64 = COPY killed $vgpr0
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bb.1:
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successors: %bb.2, %bb.1
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%1:vreg_64 = COPY killed %0
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%0:vreg_64 = COPY %1
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S_CBRANCH_EXECNZ %bb.1, implicit $exec
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S_BRANCH %bb.2
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bb.2:
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undef %0.sub1:vreg_64 = COPY %0.sub1
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S_BRANCH %bb.1
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...
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---
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name: prune_subrange_phi_value_0_1
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tracksRegLiveness: true
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body: |
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; CHECK-LABEL: name: prune_subrange_phi_value_0_1
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; CHECK: bb.0:
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; CHECK: successors: %bb.1(0x80000000)
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; CHECK: liveins: $vgpr0
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; CHECK: undef %0.sub1:vreg_64 = COPY $vgpr0
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; CHECK: bb.1:
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; CHECK: successors: %bb.2(0x40000000), %bb.1(0x40000000)
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; CHECK: S_CBRANCH_EXECNZ %bb.1, implicit $exec
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; CHECK: S_BRANCH %bb.2
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; CHECK: bb.2:
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; CHECK: successors: %bb.1(0x80000000)
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; CHECK: S_BRANCH %bb.1
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bb.0:
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liveins: $vgpr0
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undef %0.sub1:vreg_64 = COPY killed $vgpr0
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bb.1:
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successors: %bb.2, %bb.1
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%1:vreg_64 = COPY killed %0
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%0:vreg_64 = COPY %1
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S_CBRANCH_EXECNZ %bb.1, implicit $exec
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S_BRANCH %bb.2
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bb.2:
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S_BRANCH %bb.1
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...
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# Variant of testcase that asserts since there wasn't already an
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# incoming segment at the erased copy, and no valid end point.
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# ---
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# name: prune_subrange_phi_value_1
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# tracksRegLiveness: true
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# body: |
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# bb.0:
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# liveins: $vgpr0
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---
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name: prune_subrange_phi_value_1
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tracksRegLiveness: true
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body: |
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; CHECK-LABEL: name: prune_subrange_phi_value_1
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; CHECK: bb.0:
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; CHECK: successors: %bb.1(0x80000000)
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; CHECK: liveins: $vgpr0
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; CHECK: undef %0.sub1:vreg_64 = COPY $vgpr0
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; CHECK: bb.1:
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; CHECK: successors: %bb.2(0x40000000), %bb.1(0x40000000)
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; CHECK: S_CBRANCH_EXECNZ %bb.1, implicit $exec
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; CHECK: S_BRANCH %bb.2
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; CHECK: bb.2:
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; CHECK: successors: %bb.1(0x80000000)
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; CHECK: undef %0.sub1:vreg_64 = nofpexcept V_CEIL_F32_e32 %0.sub1, implicit $mode, implicit $exec
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; CHECK: S_BRANCH %bb.1
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bb.0:
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liveins: $vgpr0
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# undef %0.sub1:vreg_64 = COPY killed $vgpr0
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undef %0.sub1:vreg_64 = COPY killed $vgpr0
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# bb.1:
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# successors: %bb.2, %bb.1
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bb.1:
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successors: %bb.2, %bb.1
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# %0:vreg_64 = COPY killed %0
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# S_CBRANCH_EXECNZ %bb.1, implicit $exec
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# S_BRANCH %bb.2
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%0:vreg_64 = COPY killed %0
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S_CBRANCH_EXECNZ %bb.1, implicit $exec
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S_BRANCH %bb.2
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# bb.2:
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# undef %1.sub1:vreg_64 = nofpexcept V_CEIL_F32_e32 killed %0.sub1, implicit $mode, implicit $exec
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# %0:vreg_64 = COPY killed %1
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# S_BRANCH %bb.1
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bb.2:
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undef %1.sub1:vreg_64 = nofpexcept V_CEIL_F32_e32 killed %0.sub1, implicit $mode, implicit $exec
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%0:vreg_64 = COPY killed %1
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S_BRANCH %bb.1
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# ...
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...
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---
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name: prune_subrange_phi_value_2
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@ -0,0 +1,51 @@
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; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
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; RUN: llc -mtriple=amdgcn-amd-amdhsa -mcpu=gfx906 -verify-machineinstrs < %s | FileCheck %s
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; This example used to produce a verifier error resulting from the
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; register coalescer leaving behind a false live interval when a live
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; out copy introduced new liveness for a subregister.
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define <3 x float> @liveout_undef_subrange(<3 x float> %arg) {
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; CHECK-LABEL: liveout_undef_subrange:
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; CHECK: ; %bb.0: ; %bb
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; CHECK-NEXT: s_waitcnt vmcnt(0) expcnt(0) lgkmcnt(0)
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; CHECK-NEXT: v_add_f32_e32 v3, v2, v2
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; CHECK-NEXT: v_add_f32_e32 v1, v1, v1
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; CHECK-NEXT: v_add_f32_e32 v0, v0, v0
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; CHECK-NEXT: BB0_1: ; %bb1
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; CHECK-NEXT: ; =>This Loop Header: Depth=1
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; CHECK-NEXT: ; Child Loop BB0_2 Depth 2
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; CHECK-NEXT: s_mov_b64 s[4:5], 0
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; CHECK-NEXT: BB0_2: ; %bb1
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; CHECK-NEXT: ; Parent Loop BB0_1 Depth=1
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; CHECK-NEXT: ; => This Inner Loop Header: Depth=2
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; CHECK-NEXT: v_cmp_neq_f32_e32 vcc, 0, v2
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; CHECK-NEXT: s_or_b64 s[4:5], vcc, s[4:5]
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; CHECK-NEXT: s_andn2_b64 exec, exec, s[4:5]
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; CHECK-NEXT: s_cbranch_execnz BB0_2
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; CHECK-NEXT: ; %bb.3: ; %bb2
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; CHECK-NEXT: ; in Loop: Header=BB0_1 Depth=1
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; CHECK-NEXT: s_or_b64 exec, exec, s[4:5]
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; CHECK-NEXT: v_mul_f32_e32 v2, v3, v2
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; CHECK-NEXT: s_branch BB0_1
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bb:
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br label %bb1
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bb1: ; preds = %bb3, %bb
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%i = phi <3 x float> [ %arg, %bb ], [ %i11, %bb3 ]
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%i2 = extractelement <3 x float> %i, i64 2
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%i3 = fmul float %i2, 1.000000e+00
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%i4 = fmul nsz <3 x float> %arg, <float 2.000000e+00, float 2.000000e+00, float 2.000000e+00>
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%i5 = insertelement <3 x float> undef, float %i3, i32 0
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%i6 = shufflevector <3 x float> %i5, <3 x float> undef, <3 x i32> zeroinitializer
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%i7 = fmul <3 x float> %i4, %i6
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%i8 = fcmp oeq float %i3, 0.000000e+00
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br i1 %i8, label %bb3, label %bb2
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bb2: ; preds = %bb1
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br label %bb3
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bb3: ; preds = %bb2, %bb1
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%i11 = phi <3 x float> [ %i7, %bb2 ], [ %i, %bb1 ]
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br label %bb1
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}
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