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[LAA] Support pointer phis in loop by analyzing each incoming pointer.

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SCEV does not look through non-header PHIs inside the loop. Such phis
can be analyzed by adding separate accesses for each incoming pointer
value.

This results in 2 more loops vectorized in SPEC2000/186.crafty and
avoids regressions when sinking instructions before vectorizing.

Reviewed By: Meinersbur

Differential Revision: https://reviews.llvm.org/D101286
This commit is contained in:
Florian Hahn 2021-04-28 20:02:47 +01:00
parent c793cba446
commit 939b677f1c
3 changed files with 48 additions and 8 deletions
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25
lib/Analysis/LoopAccessAnalysis.cpp
View File

@ -1938,7 +1938,18 @@ void LoopAccessInfo::analyzeLoop(AAResults *AA, LoopInfo *LI,
if (blockNeedsPredication(ST->getParent(), TheLoop, DT))
Loc.AATags.TBAA = nullptr;
Accesses.addStore(Loc);
// SCEV does not look through non-header PHIs inside the loop. Such phis
// can be analyzed by adding separate accesses for each incoming pointer
// value.
auto *PN = dyn_cast<PHINode>(Loc.Ptr);
if (PN && TheLoop->contains(PN->getParent()) &&
PN->getParent() != TheLoop->getHeader()) {
for (const Use &Inc : PN->incoming_values()) {
MemoryLocation NewLoc = Loc.getWithNewPtr(Inc);
Accesses.addStore(NewLoc);
}
} else
Accesses.addStore(Loc);
}
}
@ -1982,7 +1993,17 @@ void LoopAccessInfo::analyzeLoop(AAResults *AA, LoopInfo *LI,
if (blockNeedsPredication(LD->getParent(), TheLoop, DT))
Loc.AATags.TBAA = nullptr;
Accesses.addLoad(Loc, IsReadOnlyPtr);
// SCEV does not look through non-header PHIs inside the loop. Such phis can
// be analyzed by adding separate accesses for each incoming pointer value.
auto *PN = dyn_cast<PHINode>(Loc.Ptr);
if (PN && TheLoop->contains(PN->getParent()) &&
PN->getParent() != TheLoop->getHeader()) {
for (const Use &Inc : PN->incoming_values()) {
MemoryLocation NewLoc = Loc.getWithNewPtr(Inc);
Accesses.addLoad(NewLoc, IsReadOnlyPtr);
}
} else
Accesses.addLoad(Loc, IsReadOnlyPtr);
}
// If we write (or read-write) to a single destination and there are no

22
test/Analysis/LoopAccessAnalysis/pointer-phis.ll
View File

@ -6,7 +6,7 @@
define i32 @load_with_pointer_phi_no_runtime_checks(%s1* %data) {
; CHECK-LABEL: load_with_pointer_phi_no_runtime_checks
; CHECK-NEXT: loop.header:
; CHECK-NEXT: Report: cannot identify array bounds
; CHECK-NEXT: Memory dependences are safe
;
entry:
br label %loop.header
@ -41,7 +41,7 @@ exit: ; preds = %loop.latch
define i32 @store_with_pointer_phi_no_runtime_checks(%s1* %data) {
; CHECK-LABEL: 'store_with_pointer_phi_no_runtime_checks'
; CHECK-NEXT: loop.header:
; CHECK-NEXT: Report: cannot identify array bounds
; CHECK-NEXT: Memory dependences are safe
;
entry:
br label %loop.header
@ -76,7 +76,23 @@ exit: ; preds = %loop.latch
define i32 @store_with_pointer_phi_runtime_checks(double* %A, double* %B, double* %C) {
; CHECK-LABEL: 'store_with_pointer_phi_runtime_checks'
; CHECK-NEXT: loop.header:
; CHECK-NEXT: Report: cannot identify array bounds
; CHECK-NEXT: Memory dependences are safe with run-time checks
; CHECK: Run-time memory checks:
; CHECK-NEXT: Check 0:
; CHECK-NEXT: Comparing group ([[GROUP_C:.+]]):
; CHECK-NEXT: %gep.2 = getelementptr inbounds double, double* %C, i64 %iv
; CHECK-NEXT: Against group ([[GROUP_B:.+]]):
; CHECK-NEXT: %gep.1 = getelementptr inbounds double, double* %B, i64 %iv
; CHECK-NEXT: Check 1:
; CHECK-NEXT: Comparing group ([[GROUP_C]]):
; CHECK-NEXT: %gep.2 = getelementptr inbounds double, double* %C, i64 %iv
; CHECK-NEXT: Against group ([[GROUP_A:.+]]):
; CHECK-NEXT: %arrayidx = getelementptr inbounds double, double* %A, i64 %iv
; CHECK-NEXT: Check 2:
; CHECK-NEXT: Comparing group ([[GROUP_B]]):
; CHECK-NEXT: %gep.1 = getelementptr inbounds double, double* %B, i64 %iv
; CHECK-NEXT: Against group ([[GROUP_A]]):
; CHECK-NEXT: %arrayidx = getelementptr inbounds double, double* %A, i64 %iv
;
entry:
br label %loop.header

9
test/Transforms/LoopVectorize/vectorize-pointer-phis.ll
View File

@ -4,7 +4,8 @@
define i32 @load_with_pointer_phi_no_runtime_checks(%s1* %data) {
; CHECK-LABEL: @load_with_pointer_phi_no_runtime_checks
; CHECK-NOT: vector.body
; CHECK-NOT: memcheck
; CHECK: vector.body:
;
entry:
br label %loop.header
@ -38,7 +39,8 @@ exit: ; preds = %loop.latch
define i32 @store_with_pointer_phi_no_runtime_checks(%s1* %data) {
; CHECK-LABEL: @store_with_pointer_phi_no_runtime_checks
; CHECK-NOT: vector.body
; CHECK-NOT: memcheck
; CHECK: vector.body
;
entry:
br label %loop.header
@ -72,7 +74,8 @@ exit: ; preds = %loop.latch
define i32 @store_with_pointer_phi_runtime_checks(double* %A, double* %B, double* %C) {
; CHECK-LABEL: @store_with_pointer_phi_runtime_checks
; CHECK-NOT: vector.body
; CHECK: memcheck
; CHECK: vector.body
;
entry:
br label %loop.header