[llvm] 1587c7e - [Scalarizer] Treat values from unreachable blocks as undef
Mikael Holmen via llvm-commits
llvm-commits at lists.llvm.org
Fri Nov 15 02:16:16 PST 2019
Author: Mikael Holmen
Date: 2019-11-15T11:13:37+01:00
New Revision: 1587c7e86f1c58e3f692f0a418e5df6aeb754bb0
URL: https://github.com/llvm/llvm-project/commit/1587c7e86f1c58e3f692f0a418e5df6aeb754bb0
DIFF: https://github.com/llvm/llvm-project/commit/1587c7e86f1c58e3f692f0a418e5df6aeb754bb0.diff
LOG: [Scalarizer] Treat values from unreachable blocks as undef
Summary:
When scalarizing PHI nodes we might try to examine/rewrite
InsertElement nodes in predecessors. If those predecessors
are unreachable from entry, then the IR in those blocks could
have unexpected properties resulting in infinite loops in
Scatterer::operator[].
By simply treating values originating from instructions in
unreachable blocks as undef we do not need to analyse them
further.
This fixes PR41723.
Reviewers: bjope
Reviewed By: bjope
Subscribers: bjope, hiraditya, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D70171
Added:
llvm/test/Transforms/Scalarizer/phi-unreachable-pred.ll
Modified:
llvm/lib/Transforms/Scalar/Scalarizer.cpp
Removed:
################################################################################
diff --git a/llvm/lib/Transforms/Scalar/Scalarizer.cpp b/llvm/lib/Transforms/Scalar/Scalarizer.cpp
index 821cb4ee85a2..003d34317f34 100644
--- a/llvm/lib/Transforms/Scalar/Scalarizer.cpp
+++ b/llvm/lib/Transforms/Scalar/Scalarizer.cpp
@@ -22,6 +22,7 @@
#include "llvm/IR/BasicBlock.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/DataLayout.h"
+#include "llvm/IR/Dominators.h"
#include "llvm/IR/DerivedTypes.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/IRBuilder.h"
@@ -174,8 +175,8 @@ struct VectorLayout {
class ScalarizerVisitor : public InstVisitor<ScalarizerVisitor, bool> {
public:
- ScalarizerVisitor(unsigned ParallelLoopAccessMDKind)
- : ParallelLoopAccessMDKind(ParallelLoopAccessMDKind) {
+ ScalarizerVisitor(unsigned ParallelLoopAccessMDKind, DominatorTree *DT)
+ : ParallelLoopAccessMDKind(ParallelLoopAccessMDKind), DT(DT) {
}
bool visit(Function &F);
@@ -215,6 +216,8 @@ class ScalarizerVisitor : public InstVisitor<ScalarizerVisitor, bool> {
GatherList Gathered;
unsigned ParallelLoopAccessMDKind;
+
+ DominatorTree *DT;
};
class ScalarizerLegacyPass : public FunctionPass {
@@ -226,6 +229,11 @@ class ScalarizerLegacyPass : public FunctionPass {
}
bool runOnFunction(Function &F) override;
+
+ void getAnalysisUsage(AnalysisUsage& AU) const override {
+ AU.addRequired<DominatorTreeWrapperPass>();
+ AU.addPreserved<DominatorTreeWrapperPass>();
+ }
};
} // end anonymous namespace
@@ -233,6 +241,7 @@ class ScalarizerLegacyPass : public FunctionPass {
char ScalarizerLegacyPass::ID = 0;
INITIALIZE_PASS_BEGIN(ScalarizerLegacyPass, "scalarizer",
"Scalarize vector operations", false, false)
+INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
INITIALIZE_PASS_END(ScalarizerLegacyPass, "scalarizer",
"Scalarize vector operations", false, false)
@@ -304,7 +313,8 @@ bool ScalarizerLegacyPass::runOnFunction(Function &F) {
Module &M = *F.getParent();
unsigned ParallelLoopAccessMDKind =
M.getContext().getMDKindID("llvm.mem.parallel_loop_access");
- ScalarizerVisitor Impl(ParallelLoopAccessMDKind);
+ DominatorTree *DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
+ ScalarizerVisitor Impl(ParallelLoopAccessMDKind, DT);
return Impl.visit(F);
}
@@ -341,6 +351,15 @@ Scatterer ScalarizerVisitor::scatter(Instruction *Point, Value *V) {
return Scatterer(BB, BB->begin(), V, &Scattered[V]);
}
if (Instruction *VOp = dyn_cast<Instruction>(V)) {
+ // When scalarizing PHI nodes we might try to examine/rewrite InsertElement
+ // nodes in predecessors. If those predecessors are unreachable from entry,
+ // then the IR in those blocks could have unexpected properties resulting in
+ // infinite loops in Scatterer::operator[]. By simply treating values
+ // originating from instructions in unreachable blocks as undef we do not
+ // need to analyse them further.
+ if (!DT->isReachableFromEntry(VOp->getParent()))
+ return Scatterer(Point->getParent(), Point->getIterator(),
+ UndefValue::get(V->getType()));
// Put the scattered form of an instruction directly after the
// instruction.
BasicBlock *BB = VOp->getParent();
@@ -857,7 +876,10 @@ PreservedAnalyses ScalarizerPass::run(Function &F, FunctionAnalysisManager &AM)
Module &M = *F.getParent();
unsigned ParallelLoopAccessMDKind =
M.getContext().getMDKindID("llvm.mem.parallel_loop_access");
- ScalarizerVisitor Impl(ParallelLoopAccessMDKind);
+ DominatorTree *DT = &AM.getResult<DominatorTreeAnalysis>(F);
+ ScalarizerVisitor Impl(ParallelLoopAccessMDKind, DT);
bool Changed = Impl.visit(F);
- return Changed ? PreservedAnalyses::none() : PreservedAnalyses::all();
+ PreservedAnalyses PA;
+ PA.preserve<DominatorTreeAnalysis>();
+ return Changed ? PA : PreservedAnalyses::all();
}
diff --git a/llvm/test/Transforms/Scalarizer/phi-unreachable-pred.ll b/llvm/test/Transforms/Scalarizer/phi-unreachable-pred.ll
new file mode 100644
index 000000000000..1de1f6509666
--- /dev/null
+++ b/llvm/test/Transforms/Scalarizer/phi-unreachable-pred.ll
@@ -0,0 +1,98 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt < %s -scalarizer -S -o - | FileCheck %s
+
+define i16 @f1() {
+; CHECK-LABEL: @f1(
+; CHECK-NEXT: entry:
+; CHECK-NEXT: br label [[FOR_END:%.*]]
+; CHECK: for.body:
+; CHECK-NEXT: [[INSERT:%.*]] = insertelement <4 x i16> [[INSERT]], i16 ptrtoint (i16 ()* @f1 to i16), i32 0
+; CHECK-NEXT: br label [[FOR_COND:%.*]]
+; CHECK: for.cond:
+; CHECK-NEXT: br i1 undef, label [[FOR_BODY:%.*]], label [[FOR_END]]
+; CHECK: for.end:
+; CHECK-NEXT: [[PHI_I0:%.*]] = phi i16 [ 1, [[ENTRY:%.*]] ], [ undef, [[FOR_COND]] ]
+; CHECK-NEXT: [[PHI_I1:%.*]] = phi i16 [ 1, [[ENTRY]] ], [ undef, [[FOR_COND]] ]
+; CHECK-NEXT: [[PHI_I2:%.*]] = phi i16 [ 1, [[ENTRY]] ], [ undef, [[FOR_COND]] ]
+; CHECK-NEXT: [[PHI_I3:%.*]] = phi i16 [ 1, [[ENTRY]] ], [ undef, [[FOR_COND]] ]
+; CHECK-NEXT: [[PHI_UPTO0:%.*]] = insertelement <4 x i16> undef, i16 [[PHI_I0]], i32 0
+; CHECK-NEXT: [[PHI_UPTO1:%.*]] = insertelement <4 x i16> [[PHI_UPTO0]], i16 [[PHI_I1]], i32 1
+; CHECK-NEXT: [[PHI_UPTO2:%.*]] = insertelement <4 x i16> [[PHI_UPTO1]], i16 [[PHI_I2]], i32 2
+; CHECK-NEXT: [[PHI:%.*]] = insertelement <4 x i16> [[PHI_UPTO2]], i16 [[PHI_I3]], i32 3
+; CHECK-NEXT: [[EXTRACT:%.*]] = extractelement <4 x i16> [[PHI]], i32 0
+; CHECK-NEXT: ret i16 [[EXTRACT]]
+;
+entry:
+ br label %for.end
+
+for.body:
+ %insert = insertelement <4 x i16> %insert, i16 ptrtoint (i16 () * @f1 to i16), i32 0
+ br label %for.cond
+
+for.cond:
+ br i1 undef, label %for.body, label %for.end
+
+for.end:
+ ; opt used to hang when scalarizing this code. When scattering %insert we
+ ; need to analyze the insertelement in the unreachable-from-entry block
+ ; for.body. Note that the insertelement instruction depends on itself, and
+ ; this kind of IR is not allowed in reachable-from-entry blocks.
+ %phi = phi <4 x i16> [ <i16 1, i16 1, i16 1, i16 1>, %entry ], [ %insert, %for.cond ]
+ %extract = extractelement <4 x i16> %phi, i32 0
+ ret i16 %extract
+}
+
+define void @f2() {
+; CHECK-LABEL: @f2(
+; CHECK-NEXT: entry:
+; CHECK-NEXT: br label [[FOR_BODY:%.*]]
+; CHECK: for.body:
+; CHECK-NEXT: br i1 undef, label [[IF_THEN:%.*]], label [[IF_END8:%.*]]
+; CHECK: if.then:
+; CHECK-NEXT: br label [[IF_END8]]
+; CHECK: for.body2:
+; CHECK-NEXT: br i1 undef, label [[FOR_END:%.*]], label [[FOR_INC:%.*]]
+; CHECK: for.end:
+; CHECK-NEXT: br label [[FOR_INC]]
+; CHECK: for.inc:
+; CHECK-NEXT: [[E_SROA_3_2:%.*]] = phi <2 x i64> [ <i64 1, i64 1>, [[FOR_END]] ], [ [[E_SROA_3_2]], [[FOR_BODY2:%.*]] ]
+; CHECK-NEXT: [[TMP0:%.*]] = phi i32 [ 6, [[FOR_END]] ], [ [[TMP0]], [[FOR_BODY2]] ]
+; CHECK-NEXT: br i1 undef, label [[FOR_BODY2]], label [[FOR_COND1_FOR_END7_CRIT_EDGE:%.*]]
+; CHECK: for.cond1.for.end7_crit_edge:
+; CHECK-NEXT: br label [[IF_END8]]
+; CHECK: if.end8:
+; CHECK-NEXT: [[E_SROA_3_4_I0:%.*]] = phi i64 [ undef, [[FOR_BODY]] ], [ undef, [[FOR_COND1_FOR_END7_CRIT_EDGE]] ], [ undef, [[IF_THEN]] ]
+; CHECK-NEXT: [[E_SROA_3_4_I1:%.*]] = phi i64 [ undef, [[FOR_BODY]] ], [ undef, [[FOR_COND1_FOR_END7_CRIT_EDGE]] ], [ undef, [[IF_THEN]] ]
+; CHECK-NEXT: br label [[FOR_BODY]]
+;
+entry:
+ br label %for.body
+
+for.body: ; preds = %if.end8, %entry
+ br i1 undef, label %if.then, label %if.end8
+
+if.then: ; preds = %for.body
+ br label %if.end8
+
+for.body2: ; preds = %for.inc
+ br i1 undef, label %for.end, label %for.inc
+
+for.end: ; preds = %for.body2
+ br label %for.inc
+
+for.inc: ; preds = %for.end, %for.body2
+ %e.sroa.3.2 = phi <2 x i64> [ <i64 1, i64 1>, %for.end ], [ %e.sroa.3.2, %for.body2 ]
+ %0 = phi i32 [ 6, %for.end ], [ %0, %for.body2 ]
+ br i1 undef, label %for.body2, label %for.cond1.for.end7_crit_edge
+
+for.cond1.for.end7_crit_edge: ; preds = %for.inc
+ br label %if.end8
+
+if.end8: ; preds = %for.cond1.for.end7_crit_edge, %if.then, %for.body
+ ; This used to lead to inserted extractelement instructions between the phis
+ ; in %for.inc.
+ ; %e.sroa.3.2 is defined in a block that is unreachable from entry so we can
+ ; safely replace it with undef in the phi defining e.sroa.3.4.
+ %e.sroa.3.4 = phi <2 x i64> [ undef, %for.body ], [ %e.sroa.3.2, %for.cond1.for.end7_crit_edge ], [ undef, %if.then ]
+ br label %for.body
+}
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