[llvm] r277649 - GVN-hoist: compute MSSA once per function (PR28670)
Sebastian Pop via llvm-commits
llvm-commits at lists.llvm.org
Wed Aug 3 13:54:34 PDT 2016
Author: spop
Date: Wed Aug 3 15:54:33 2016
New Revision: 277649
URL: http://llvm.org/viewvc/llvm-project?rev=277649&view=rev
Log:
GVN-hoist: compute MSSA once per function (PR28670)
With this patch we compute the MemorySSA once and update it in the code generator.
Differential Revision: https://reviews.llvm.org/D22966
Added:
llvm/trunk/test/Transforms/GVN/hoist-mssa.ll
Modified:
llvm/trunk/lib/Transforms/Scalar/GVNHoist.cpp
Modified: llvm/trunk/lib/Transforms/Scalar/GVNHoist.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/GVNHoist.cpp?rev=277649&r1=277648&r2=277649&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Scalar/GVNHoist.cpp (original)
+++ llvm/trunk/lib/Transforms/Scalar/GVNHoist.cpp Wed Aug 3 15:54:33 2016
@@ -193,14 +193,11 @@ public:
VN.setAliasAnalysis(AA);
VN.setMemDep(MD);
bool Res = false;
+ MemorySSA M(F, AA, DT);
+ MSSA = &M;
// FIXME: use lazy evaluation of VN to avoid the fix-point computation.
while (1) {
- // FIXME: only compute MemorySSA once. We need to update the analysis in
- // the same time as transforming the code.
- MemorySSA M(F, AA, DT);
- MSSA = &M;
-
// Perform DFS Numbering of instructions.
unsigned I = 0;
for (const BasicBlock *BB : depth_first(&F.getEntryBlock()))
@@ -208,15 +205,15 @@ public:
DFSNumber.insert({&Inst, ++I});
auto HoistStat = hoistExpressions(F);
- if (HoistStat.first + HoistStat.second == 0) {
+ if (HoistStat.first + HoistStat.second == 0)
return Res;
- }
- if (HoistStat.second > 0) {
+
+ if (HoistStat.second > 0)
// To address a limitation of the current GVN, we need to rerun the
- // hoisting after we hoisted loads in order to be able to hoist all
- // scalars dependent on the hoisted loads. Same for stores.
+ // hoisting after we hoisted loads or stores in order to be able to
+ // hoist all scalars dependent on the hoisted ld/st.
VN.clear();
- }
+
Res = true;
// DFS numbers change when instructions are hoisted: clear and recompute.
@@ -310,7 +307,8 @@ private:
for (User *U : Def->users())
if (auto *MU = dyn_cast<MemoryUse>(U)) {
- BasicBlock *UBB = MU->getBlock();
+ // FIXME: MU->getBlock() does not get updated when we move the instruction.
+ BasicBlock *UBB = MU->getMemoryInst()->getParent();
// Only analyze uses in BB.
if (BB != UBB)
continue;
@@ -742,9 +740,23 @@ private:
!makeGepOperandsAvailable(Repl, HoistPt, InstructionsToHoist))
continue;
+ // Move the instruction at the end of HoistPt.
Repl->moveBefore(HoistPt->getTerminator());
}
+ MemoryAccess *NewMemAcc = nullptr;
+ if (MemoryAccess *MA = MSSA->getMemoryAccess(Repl)) {
+ if (MemoryUseOrDef *OldMemAcc = dyn_cast<MemoryUseOrDef>(MA)) {
+ // The definition of this ld/st will not change: ld/st hoisting is
+ // legal when the ld/st is not moved past its current definition.
+ MemoryAccess *Def = OldMemAcc->getDefiningAccess();
+ NewMemAcc = MSSA->createMemoryAccessInBB(Repl, Def, HoistPt,
+ MemorySSA::End);
+ OldMemAcc->replaceAllUsesWith(NewMemAcc);
+ MSSA->removeMemoryAccess(OldMemAcc);
+ }
+ }
+
if (isa<LoadInst>(Repl))
++NL;
else if (isa<StoreInst>(Repl))
@@ -775,11 +787,36 @@ private:
} else if (isa<CallInst>(Repl)) {
++NumCallsRemoved;
}
+
+ if (NewMemAcc) {
+ // Update the uses of the old MSSA access with NewMemAcc.
+ MemoryAccess *OldMA = MSSA->getMemoryAccess(I);
+ OldMA->replaceAllUsesWith(NewMemAcc);
+ MSSA->removeMemoryAccess(OldMA);
+ }
+
Repl->intersectOptionalDataWith(I);
combineKnownMetadata(Repl, I);
I->replaceAllUsesWith(Repl);
I->eraseFromParent();
}
+
+ // Remove MemorySSA phi nodes with the same arguments.
+ if (NewMemAcc) {
+ SmallPtrSet<MemoryPhi *, 4> UsePhis;
+ for (User *U : NewMemAcc->users())
+ if (MemoryPhi *Phi = dyn_cast<MemoryPhi>(U))
+ UsePhis.insert(Phi);
+
+ for (auto *Phi : UsePhis) {
+ auto In = Phi->incoming_values();
+ if (std::all_of(In.begin(), In.end(),
+ [&](Use &U){return U == NewMemAcc;})) {
+ Phi->replaceAllUsesWith(NewMemAcc);
+ MSSA->removeMemoryAccess(Phi);
+ }
+ }
+ }
}
NumHoisted += NL + NS + NC + NI;
Added: llvm/trunk/test/Transforms/GVN/hoist-mssa.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/GVN/hoist-mssa.ll?rev=277649&view=auto
==============================================================================
--- llvm/trunk/test/Transforms/GVN/hoist-mssa.ll (added)
+++ llvm/trunk/test/Transforms/GVN/hoist-mssa.ll Wed Aug 3 15:54:33 2016
@@ -0,0 +1,69 @@
+; RUN: opt -S -gvn-hoist < %s | FileCheck %s
+
+; Check that store hoisting works: there should be only one store left.
+; CHECK-LABEL: @getopt
+; CHECK: store i32
+; CHECK-NOT: store i32
+
+ at optind = external global i32, align 4
+
+define void @getopt() {
+bb:
+ br label %bb1
+
+bb1: ; preds = %bb
+ br i1 undef, label %bb2, label %bb3
+
+bb2: ; preds = %bb1
+ br label %bb13
+
+bb3: ; preds = %bb1
+ br i1 undef, label %bb4, label %bb9
+
+bb4: ; preds = %bb3
+ %tmp = load i32, i32* @optind, align 4
+ br i1 undef, label %bb5, label %bb7
+
+bb5: ; preds = %bb4
+ %tmp6 = add nsw i32 %tmp, 1
+ store i32 %tmp6, i32* @optind, align 4
+ br label %bb12
+
+bb7: ; preds = %bb4
+ %tmp8 = add nsw i32 %tmp, 1
+ store i32 %tmp8, i32* @optind, align 4
+ br label %bb13
+
+bb9: ; preds = %bb3
+ %tmp10 = load i32, i32* @optind, align 4
+ %tmp11 = add nsw i32 %tmp10, 1
+ store i32 %tmp11, i32* @optind, align 4
+ br label %bb12
+
+bb12: ; preds = %bb9, %bb5
+ br label %bb13
+
+bb13: ; preds = %bb12, %bb7, %bb2
+ ret void
+}
+
+ at GlobalVar = internal global float 1.000000e+00
+
+; Check that we hoist stores and remove the MSSA phi node.
+; CHECK-LABEL: @hoistStoresUpdateMSSA
+; CHECK: store float
+; CHECK-NOT: store float
+define float @hoistStoresUpdateMSSA(float %d) {
+entry:
+ store float 0.000000e+00, float* @GlobalVar
+ %cmp = fcmp oge float %d, 0.000000e+00
+ br i1 %cmp, label %if.then, label %if.end
+
+if.then:
+ store float 0.000000e+00, float* @GlobalVar
+ br label %if.end
+
+if.end:
+ %tmp = load float, float* @GlobalVar, align 4
+ ret float %tmp
+}
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