[PATCH] D78667: [ValueLattice] Merging unknown with empty CR is unknown.

Wed Apr 22 13:37:29 PDT 2020

fhahn created this revision.
fhahn added reviewers: efriedma, nikic, davide.
Herald added a project: LLVM.

Currently an unknown/undef value is marked as overdefined when merged
with an empty range. An empty range can occur in unreachable/dead code.
When merging the new unknown state (= no value known yet) with an empty
range, there still isn't any information about the value yet and we can
stay in unknown.

This gives a few nice improvements on the number of instructions removed
by IPSCCP:
Same hash: 170 (filtered out)
Remaining: 67
Metric: sccp.IPNumInstRemoved

Program                                        base     patch    diff
 test-suite...rks/FreeBench/mason/mason.test     3.00   6.00 100.0%
 test-suite...nchmarks/McCat/18-imp/imp.test     3.00   5.00 66.7%
 test-suite...C/CFP2000/179.art/179.art.test     2.00   3.00 50.0%
 test-suite...ijndael/security-rijndael.test     2.00   3.00 50.0%
 test-suite...ks/Prolangs-C/agrep/agrep.test    40.00  58.00 45.0%
 test-suite...ce/Applications/Burg/burg.test    26.00  37.00 42.3%
 test-suite...cCat/03-testtrie/testtrie.test     3.00   4.00 33.3%
 test-suite...Source/Benchmarks/sim/sim.test    29.00  36.00 24.1%
 test-suite.../Applications/spiff/spiff.test     9.00  11.00 22.2%
 test-suite...s/FreeBench/neural/neural.test     5.00   6.00 20.0%
 test-suite...pplications/treecc/treecc.test    66.00  79.00 19.7%
 test-suite...langs-C/football/football.test    85.00 101.00 18.8%
 test-suite...ce/Benchmarks/PAQ8p/paq8p.test    90.00 105.00 16.7%
 test-suite...oxyApps-C++/miniFE/miniFE.test    37.00  43.00 16.2%
 test-suite...rks/FreeBench/pifft/pifft.test    26.00  30.00 15.4%
 test-suite...lications/sqlite3/sqlite3.test   481.00  548.00  13.9%
 test-suite...marks/7zip/7zip-benchmark.test   4875.00 5522.00 13.3%
 test-suite.../CINT2000/176.gcc/176.gcc.test   1117.00 1197.00  7.2%
 test-suite...0.perlbench/400.perlbench.test   1618.00 1732.00  7.0%


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D78667

Files:
  llvm/include/llvm/Analysis/ValueLattice.h
  llvm/test/Transforms/CorrelatedValuePropagation/sub.ll
  llvm/test/Transforms/SCCP/widening.ll


Index: llvm/test/Transforms/SCCP/widening.ll
===================================================================

--- llvm/test/Transforms/SCCP/widening.ll
+++ llvm/test/Transforms/SCCP/widening.ll
@@ -744,11 +744,10 @@
 ; IPSCCP-NEXT:    [[C_2:%.*]] = icmp eq i32 [[TMP11]], 8
 ; IPSCCP-NEXT:    br i1 [[C_2]], label [[BB39:%.*]], label [[BB58:%.*]]
 ; IPSCCP:       bb39:
-; IPSCCP-NEXT:    [[TMP40:%.*]] = add nsw i32 [[TMP11]], -1
 ; IPSCCP-NEXT:    [[TMP41:%.*]] = trunc i32 [[TMP3]] to i16
 ; IPSCCP-NEXT:    store i16 [[TMP41]], i16* bitcast ([4 x i8]* @global.11 to i16*), align 1
 ; IPSCCP-NEXT:    [[TMP42:%.*]] = getelementptr inbounds [[STRUCT_BLAM_2]], %struct.blam.2* [[ARG]], i32 0, i32 0
-; IPSCCP-NEXT:    [[TMP43:%.*]] = add i32 [[TMP7]], [[TMP40]]
+; IPSCCP-NEXT:    [[TMP43:%.*]] = add i32 [[TMP7]], 7
 ; IPSCCP-NEXT:    [[TMP44:%.*]] = mul i32 [[TMP43]], 4
 ; IPSCCP-NEXT:    [[TMP45:%.*]] = add i32 [[TMP44]], 2
 ; IPSCCP-NEXT:    [[TMP46:%.*]] = call dereferenceable(1) i8* @spam(%struct.baz.1* [[TMP42]], i32 [[TMP45]])
@@ -763,14 +762,13 @@
 ; IPSCCP-NEXT:    [[TMP55:%.*]] = icmp sgt i32 [[TMP48]], [[TMP54]]
 ; IPSCCP-NEXT:    br i1 [[TMP55]], label [[BB56:%.*]], label [[BB60:%.*]]
 ; IPSCCP:       bb56:
-; IPSCCP-NEXT:    [[TMP57:%.*]] = add nsw i32 [[TMP40]], -1
 ; IPSCCP-NEXT:    br label [[BB60]]
 ; IPSCCP:       bb58:
 ; IPSCCP-NEXT:    [[TMP59:%.*]] = bitcast i16* [[TMP33]] to i8*
 ; IPSCCP-NEXT:    call void @llvm.memcpy.p0i8.p0i8.i64(i8* align 1 getelementptr inbounds ([4 x i8], [4 x i8]* @global.11, i64 0, i64 0), i8* align 2 [[TMP59]], i64 4, i1 false)
 ; IPSCCP-NEXT:    br label [[BB60]]
 ; IPSCCP:       bb60:
-; IPSCCP-NEXT:    [[TMP61:%.*]] = phi i32 [ [[TMP57]], [[BB56]] ], [ [[TMP40]], [[BB39]] ], [ [[TMP11]], [[BB58]] ]
+; IPSCCP-NEXT:    [[TMP61:%.*]] = phi i32 [ 6, [[BB56]] ], [ 7, [[BB39]] ], [ [[TMP11]], [[BB58]] ]
 ; IPSCCP-NEXT:    [[TMP62:%.*]] = getelementptr inbounds [[STRUCT_BLAM_2]], %struct.blam.2* [[ARG]], i32 0, i32 0
 ; IPSCCP-NEXT:    [[TMP63:%.*]] = add i32 [[TMP7]], 1
 ; IPSCCP-NEXT:    [[TMP64:%.*]] = mul i32 [[TMP63]], 4
Index: llvm/test/Transforms/CorrelatedValuePropagation/sub.ll
===================================================================
--- llvm/test/Transforms/CorrelatedValuePropagation/sub.ll
+++ llvm/test/Transforms/CorrelatedValuePropagation/sub.ll
@@ -53,7 +53,7 @@
 ; CHECK-NEXT:    [[CMP:%.*]] = icmp ugt i32 [[A:%.*]], -1
 ; CHECK-NEXT:    br i1 [[CMP]], label [[BB:%.*]], label [[EXIT:%.*]]
 ; CHECK:       bb:
-; CHECK-NEXT:    [[SUB:%.*]] = sub i32 [[A]], 1
+; CHECK-NEXT:    [[SUB:%.*]] = sub nuw nsw i32 [[A]], 1
 ; CHECK-NEXT:    br label [[EXIT]]
 ; CHECK:       exit:
 ; CHECK-NEXT:    ret void
Index: llvm/include/llvm/Analysis/ValueLattice.h
===================================================================
--- llvm/include/llvm/Analysis/ValueLattice.h
+++ llvm/include/llvm/Analysis/ValueLattice.h
@@ -353,8 +353,11 @@
     }
 
     assert(isUnknown() || isUndef());
-    if (NewR.isEmptySet())
+    if (NewR.isEmptySet()) {
+      if (isUnknown())
+        return false;
       return markOverdefined();
+    }
 
     NumRangeExtensions = 0;
     Tag = NewTag;


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