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[DSE] Look through memory PHI arguments when removing noop stores in MSSA.
Summary: Adds support for "following" memory through MSSA PHI arguments. This will help catch more noop stores that exist between blocks. Originally part of D79391. Reviewers: fhahn, jfb, asbirlea Differential Revision: https://reviews.llvm.org/D82588
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@ -2404,10 +2404,44 @@ struct DSEState {
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if (auto *LoadI = dyn_cast<LoadInst>(Store->getOperand(0))) {
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if (LoadI->getPointerOperand() == Store->getOperand(1)) {
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// Get the defining access for the load.
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auto *LoadAccess = MSSA.getMemoryAccess(LoadI)->getDefiningAccess();
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// If both accesses share the same defining access, no instructions
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// between them can modify the memory location.
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return LoadAccess == Def->getDefiningAccess();
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// Fast path: the defining accesses are the same.
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if (LoadAccess == Def->getDefiningAccess())
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return true;
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// Look through phi accesses. Recursively scan all phi accesses by
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// adding them to a worklist. Bail when we run into a memory def that
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// does not match LoadAccess.
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SetVector<MemoryAccess *> ToCheck;
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MemoryAccess *Current = Def->getDefiningAccess();
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// We don't want to bail when we run into the store memory def. But,
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// the phi access may point to it. So, pretend like we've already
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// checked it.
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ToCheck.insert(Def);
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ToCheck.insert(Current);
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// Start at current (1) to simulate already having checked Def.
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for (unsigned I = 1; I < ToCheck.size(); ++I) {
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Current = ToCheck[I];
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if (auto PhiAccess = dyn_cast<MemoryPhi>(Current)) {
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// Check all the operands.
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for (auto &Use : PhiAccess->incoming_values())
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ToCheck.insert(cast<MemoryAccess>(&Use));
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continue;
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}
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// If we found a memory def, bail. This happens when we have an
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// unrelated write in between an otherwise noop store.
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assert(isa<MemoryDef>(Current) &&
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"Only MemoryDefs should reach here.");
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// TODO: Skip no alias MemoryDefs that have no aliasing reads.
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// We are searching for the definition of the store's destination.
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// So, if that is the same definition as the load, then this is a
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// noop. Otherwise, fail.
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if (LoadAccess != Current)
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return false;
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}
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return true;
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}
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}
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@ -101,6 +101,47 @@ bb3:
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ret i32 0
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}
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; Remove redundant store if loaded value is in another block inside a loop.
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define i32 @test31(i1 %c, i32* %p, i32 %i) {
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; CHECK-LABEL: @test31(
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; CHECK-NEXT: entry:
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; CHECK-NEXT: br label [[BB1:%.*]]
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; CHECK: bb1:
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; CHECK-NEXT: br i1 [[C:%.*]], label [[BB1]], label [[BB2:%.*]]
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; CHECK: bb2:
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; CHECK-NEXT: ret i32 0
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;
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entry:
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%v = load i32, i32* %p, align 4
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br label %bb1
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bb1:
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store i32 %v, i32* %p, align 4
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br i1 %c, label %bb1, label %bb2
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bb2:
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ret i32 0
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}
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; Don't remove "redundant" store if %p is possibly stored to.
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define i32 @test46(i1 %c, i32* %p, i32* %p2, i32 %i) {
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; CHECK-LABEL: @test46(
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; CHECK: load
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; CHECK: store
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; CHECK: store
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; CHECK: ret i32 0
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;
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entry:
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%v = load i32, i32* %p, align 4
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br label %bb1
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bb1:
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store i32 %v, i32* %p, align 4
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br i1 %c, label %bb1, label %bb2
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bb2:
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store i32 0, i32* %p2, align 4
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br i1 %c, label %bb3, label %bb1
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bb3:
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ret i32 0
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}
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declare void @unknown_func()
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; Remove redundant store, which is in the lame loop as the load.
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@ -112,7 +153,7 @@ define i32 @test33(i1 %c, i32* %p, i32 %i) {
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; CHECK-NEXT: br label [[BB2:%.*]]
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; CHECK: bb2:
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; CHECK-NEXT: call void @unknown_func()
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; CHECK-NEXT: br i1 undef, label [[BB1]], label [[BB3:%.*]]
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; CHECK-NEXT: br i1 [[C:%.*]], label [[BB1]], label [[BB3:%.*]]
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; CHECK: bb3:
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; CHECK-NEXT: ret i32 0
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;
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@ -125,7 +166,7 @@ bb2:
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store i32 %v, i32* %p, align 4
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; Might read and overwrite value at %p, but doesn't matter.
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call void @unknown_func()
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br i1 undef, label %bb1, label %bb3
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br i1 %c, label %bb1, label %bb3
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bb3:
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ret i32 0
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}
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@ -168,4 +209,52 @@ define void @test45(i32* %Q) {
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ret void
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}
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define i32 @test48(i1 %c, i32* %p) {
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; CHECK-LABEL: @test48(
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; CHECK: entry:
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; CHECK-NEXT: [[V:%.*]] = load
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; CHECK: store i32 0
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; CHECK: store i32 [[V]]
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; CHECK: ret i32 0
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entry:
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%v = load i32, i32* %p, align 4
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br i1 %c, label %bb0, label %bb0.0
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bb0:
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store i32 0, i32* %p
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br i1 %c, label %bb1, label %bb2
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bb0.0:
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br label %bb1
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bb1:
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store i32 %v, i32* %p, align 4
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br i1 %c, label %bb2, label %bb0
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bb2:
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ret i32 0
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}
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; TODO: Remove both redundant stores if loaded value is in another block inside a loop.
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define i32 @test47(i1 %c, i32* %p, i32 %i) {
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; X-CHECK-LABEL: @test47(
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; X-CHECK-NEXT: entry:
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; X-CHECK-NEXT: br label [[BB1:%.*]]
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; X-CHECK: bb1:
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; X-CHECK-NEXT: br i1 [[C:%.*]], label [[BB1]], label [[BB2:%.*]]
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; X-CHECK: bb2:
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; X-CHECK-NEXT: br i1 [[C]], label [[BB2]], label [[BB3:%.*]]
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; X-CHECK: bb3:
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; X-CHECK-NEXT: ret i32 0
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entry:
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%v = load i32, i32* %p, align 4
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br label %bb1
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bb1:
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store i32 %v, i32* %p, align 4
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br i1 %c, label %bb1, label %bb2
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bb2:
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store i32 %v, i32* %p, align 4
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br i1 %c, label %bb3, label %bb1
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bb3:
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ret i32 0
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}
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@ -1,25 +0,0 @@
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; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
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; XFAIL: *
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; RUN: opt < %s -basic-aa -dse -enable-dse-memoryssa -S | FileCheck %s
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; RUN: opt < %s -aa-pipeline=basic-aa -passes=dse -enable-dse-memoryssa -S | FileCheck %s
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target datalayout = "E-p:64:64:64-a0:0:8-f32:32:32-f64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:32:64-v64:64:64-v128:128:128"
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; Remove redundant store if loaded value is in another block inside a loop.
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define i32 @test31(i1 %c, i32* %p, i32 %i) {
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; CHECK-LABEL: @test31(
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; CHECK-NEXT: entry:
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; CHECK-NEXT: br label [[BB1:%.*]]
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; CHECK: bb1:
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; CHECK-NEXT: br i1 undef, label [[BB1]], label [[BB2:%.*]]
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; CHECK: bb2:
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; CHECK-NEXT: ret i32 0
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;
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entry:
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%v = load i32, i32* %p, align 4
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br label %bb1
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bb1:
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store i32 %v, i32* %p, align 4
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br i1 undef, label %bb1, label %bb2
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bb2:
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ret i32 0
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}
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