[llvm] e3d8cb1 - [InstCombine] Negator: cache negation results (PR46362)
Roman Lebedev via llvm-commits
llvm-commits at lists.llvm.org
Wed Jun 17 12:48:14 PDT 2020
Author: Roman Lebedev
Date: 2020-06-17T22:47:20+03:00
New Revision: e3d8cb1e1d227c61576914e42435b5e71d442631
URL: https://github.com/llvm/llvm-project/commit/e3d8cb1e1d227c61576914e42435b5e71d442631
DIFF: https://github.com/llvm/llvm-project/commit/e3d8cb1e1d227c61576914e42435b5e71d442631.diff
LOG: [InstCombine] Negator: cache negation results (PR46362)
It is possible that we can try to negate the same value multiple times.
For example, PHI nodes may happen to have multiple incoming values
(all of which must be the same value) for the same incoming basic block.
It may happen that we try to negate such a PHI node, and succeed,
and that might result in having now-different incoming values..
To avoid that, and in general to reduce the amount of duplicated
work we might be doing, let's introduce a cache where
we'll track results of negating each value.
The added test was previously failing -verify after -instcombine.
Fixes https://bugs.llvm.org/show_bug.cgi?id=46362
Added:
Modified:
llvm/lib/Transforms/InstCombine/InstCombineInternal.h
llvm/lib/Transforms/InstCombine/InstCombineNegator.cpp
llvm/test/Transforms/InstCombine/sub-of-negatible.ll
Removed:
################################################################################
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineInternal.h b/llvm/lib/Transforms/InstCombine/InstCombineInternal.h
index 29fcc3c1f2f7..2ad9c7396f93 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineInternal.h
+++ b/llvm/lib/Transforms/InstCombine/InstCombineInternal.h
@@ -16,6 +16,7 @@
#define LLVM_LIB_TRANSFORMS_INSTCOMBINE_INSTCOMBINEINTERNAL_H
#include "llvm/ADT/ArrayRef.h"
+#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/Analysis/InstructionSimplify.h"
@@ -1040,6 +1041,8 @@ class Negator final {
const bool IsTrulyNegation;
+ SmallDenseMap<Value *, Value *> NegationsCache;
+
Negator(LLVMContext &C, const DataLayout &DL, AssumptionCache &AC,
const DominatorTree &DT, bool IsTrulyNegation);
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineNegator.cpp b/llvm/lib/Transforms/InstCombine/InstCombineNegator.cpp
index f613a6c66406..deb14f1818ef 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineNegator.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineNegator.cpp
@@ -14,6 +14,7 @@
#include "InstCombineInternal.h"
#include "llvm/ADT/APInt.h"
#include "llvm/ADT/ArrayRef.h"
+#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/None.h"
#include "llvm/ADT/Optional.h"
#include "llvm/ADT/STLExtras.h"
@@ -43,6 +44,7 @@
#include "llvm/Support/raw_ostream.h"
#include <functional>
#include <tuple>
+#include <type_traits>
#include <utility>
namespace llvm {
@@ -68,6 +70,8 @@ STATISTIC(NegatorTimesDepthLimitReached,
STATISTIC(
NegatorNumValuesVisited,
"Negator: Total number of values visited during attempts to sink negation");
+STATISTIC(NegatorNumNegationsFoundInCache,
+ "Negator: How many negations did we retrieve/reuse from cache");
STATISTIC(NegatorMaxTotalValuesVisited,
"Negator: Maximal number of values ever visited while attempting to "
"sink negation");
@@ -384,8 +388,19 @@ LLVM_NODISCARD Value *Negator::negate(Value *V, unsigned Depth) {
++NumValuesVisitedInThisNegator;
#endif
- // Try negating the value.
- return visitImpl(V, Depth);
+ // Did we already try to negate this value?
+ auto NegationsCacheIterator = NegationsCache.find(V);
+ if (NegationsCacheIterator != NegationsCache.end()) {
+ ++NegatorNumNegationsFoundInCache;
+ return NegationsCacheIterator->second;
+ }
+
+ // No luck. Try negating it for real.
+ Value *NegatedV = visitImpl(V, Depth);
+ // And cache the result for the future.
+ NegationsCache[V] = NegatedV;
+
+ return NegatedV;
}
LLVM_NODISCARD Optional<Negator::Result> Negator::run(Value *Root) {
diff --git a/llvm/test/Transforms/InstCombine/sub-of-negatible.ll b/llvm/test/Transforms/InstCombine/sub-of-negatible.ll
index 79d1e584fe19..f913de3c653f 100644
--- a/llvm/test/Transforms/InstCombine/sub-of-negatible.ll
+++ b/llvm/test/Transforms/InstCombine/sub-of-negatible.ll
@@ -4,6 +4,7 @@
declare void @use4(i4)
declare void @use8(i8)
declare void @use_v2i4(<2 x i4>)
+declare i1 @use32gen1(i32)
; Constant can be freely negated.
define i8 @t0(i8 %x) {
@@ -349,6 +350,44 @@ end:
%n = sub i8 0, %r
ret i8 %n
}
+define void @phi_with_duplicate_incoming_basic_blocks(i32 %x, i32 %y, i1 %should_lookup, i32 %z) {
+; CHECK-LABEL: @phi_with_duplicate_incoming_basic_blocks(
+; CHECK-NEXT: entry:
+; CHECK-NEXT: [[X_INC_NEG:%.*]] = xor i32 [[X:%.*]], -1
+; CHECK-NEXT: br i1 [[SHOULD_LOOKUP:%.*]], label [[LOOKUP:%.*]], label [[LOOP:%.*]]
+; CHECK: lookup:
+; CHECK-NEXT: [[TO_LOOKUP:%.*]] = phi i32 [ [[Y:%.*]], [[ENTRY:%.*]] ], [ [[METAVAL_NEG:%.*]], [[LOOP]] ]
+; CHECK-NEXT: switch i32 [[TO_LOOKUP]], label [[END:%.*]] [
+; CHECK-NEXT: i32 0, label [[LOOP]]
+; CHECK-NEXT: i32 42, label [[LOOP]]
+; CHECK-NEXT: ]
+; CHECK: loop:
+; CHECK-NEXT: [[METAVAL_NEG]] = phi i32 [ [[X_INC_NEG]], [[LOOKUP]] ], [ [[X_INC_NEG]], [[LOOKUP]] ], [ -84, [[ENTRY]] ]
+; CHECK-NEXT: [[REPEAT:%.*]] = call i1 @use32gen1(i32 [[METAVAL_NEG]])
+; CHECK-NEXT: br i1 [[REPEAT]], label [[LOOKUP]], label [[END]]
+; CHECK: end:
+; CHECK-NEXT: ret void
+;
+entry:
+ %x_inc = add i32 %x, 1
+ br i1 %should_lookup, label %lookup, label %loop
+
+lookup:
+ %to_lookup = phi i32 [ %y, %entry ], [ %negated_metaval, %loop ]
+ switch i32 %to_lookup, label %end [
+ i32 0, label %loop
+ i32 42, label %loop
+ ]
+
+loop:
+ %metaval = phi i32 [ %x_inc, %lookup ], [ %x_inc, %lookup ], [ 84, %entry ]
+ %negated_metaval = sub i32 0, %metaval
+ %repeat = call i1 @use32gen1(i32 %negated_metaval)
+ br i1 %repeat, label %lookup, label %end
+
+end:
+ ret void
+}
; truncation can be negated if it's operand can be negated
define i8 @t20(i8 %x, i16 %y) {
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