[memcpyopt] Teach memcpyopt to optimize across basic blocks

This teaches memcpyopt to make a non-local memdep query when a local query
indicates that the dependency is non-local. This notably allows it to
eliminate many more llvm.memcpy calls in common Rust code, often by 20-30%.

Fixes PR28958.

Differential Revision: https://reviews.llvm.org/D38374

llvm-svn: 319482

llvm/lib/Analysis/MemoryDependenceAnalysis.cpp

@@ -919,6 +919,14 @@ void MemoryDependenceResults::getNonLocalPointerDependency(
     Instruction *QueryInst, SmallVectorImpl<NonLocalDepResult> &Result) {
   const MemoryLocation Loc = MemoryLocation::get(QueryInst);
   bool isLoad = isa<LoadInst>(QueryInst);
+  return getNonLocalPointerDependencyFrom(QueryInst, Loc, isLoad, Result);
+}
+
+void MemoryDependenceResults::getNonLocalPointerDependencyFrom(
+    Instruction *QueryInst,
+    const MemoryLocation &Loc,
+    bool isLoad,
+    SmallVectorImpl<NonLocalDepResult> &Result) {
   BasicBlock *FromBB = QueryInst->getParent();
   assert(FromBB);
 

llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp

@@ -1031,9 +1031,22 @@ bool MemCpyOptPass::processMemCpyMemCpyDependence(MemCpyInst *M,
   //
   // NOTE: This is conservative, it will stop on any read from the source loc,
   // not just the defining memcpy.
-  MemDepResult SourceDep =
-      MD->getPointerDependencyFrom(MemoryLocation::getForSource(MDep), false,
-                                   M->getIterator(), M->getParent());
+  MemoryLocation SourceLoc = MemoryLocation::getForSource(MDep);
+  MemDepResult SourceDep = MD->getPointerDependencyFrom(SourceLoc, false,
+                                                        M->getIterator(), M->getParent());
+
+  if (SourceDep.isNonLocal()) {
+    SmallVector<NonLocalDepResult, 2> NonLocalDepResults;
+    MD->getNonLocalPointerDependencyFrom(M, SourceLoc, /*isLoad=*/false,
+                                         NonLocalDepResults);
+    if (NonLocalDepResults.size() == 1) {
+      SourceDep = NonLocalDepResults[0].getResult();
+      assert((!SourceDep.getInst() ||
+              LookupDomTree().dominates(SourceDep.getInst(), M)) &&
+             "when memdep returns exactly one result, it should dominate");
+    }
+  }
+
   if (!SourceDep.isClobber() || SourceDep.getInst() != MDep)
     return false;
 
@@ -1235,6 +1248,18 @@ bool MemCpyOptPass::processMemCpy(MemCpyInst *M) {
   MemDepResult SrcDepInfo = MD->getPointerDependencyFrom(
       SrcLoc, true, M->getIterator(), M->getParent());
 
+  if (SrcDepInfo.isNonLocal()) {
+    SmallVector<NonLocalDepResult, 2> NonLocalDepResults;
+    MD->getNonLocalPointerDependencyFrom(M, SrcLoc, /*isLoad=*/true,
+                                         NonLocalDepResults);
+    if (NonLocalDepResults.size() == 1) {
+      SrcDepInfo = NonLocalDepResults[0].getResult();
+      assert((!SrcDepInfo.getInst() ||
+              LookupDomTree().dominates(SrcDepInfo.getInst(), M)) &&
+             "when memdep returns exactly one result, it should dominate");
+    }
+  }
+
   if (SrcDepInfo.isClobber()) {
     if (MemCpyInst *MDep = dyn_cast<MemCpyInst>(SrcDepInfo.getInst()))
       return processMemCpyMemCpyDependence(M, MDep);

llvm/test/Transforms/MemCpyOpt/memcpy-invoke-memcpy.ll

@@ -0,0 +1,48 @@
+; RUN: opt < %s -memcpyopt -S | FileCheck %s
+; Test memcpy-memcpy dependencies across invoke edges.
+
+; Test that memcpyopt works across the non-unwind edge of an invoke.
+
+define hidden void @test_normal(i8* noalias %dst, i8* %src) personality i8* bitcast (i32 (...)* @__gxx_personality_v0 to i8*) {
+entry:
+  %temp = alloca i8, i32 64
+  call void @llvm.memcpy.p0i8.p0i8.i64(i8* %temp, i8* nonnull %src, i64 64, i32 8, i1 false)
+; CHECK: call void @llvm.memcpy.p0i8.p0i8.i64(i8* %temp, i8* nonnull %src, i64 64, i32 8, i1 false)
+  invoke void @invoke_me()
+          to label %try.cont unwind label %lpad
+
+lpad:
+  landingpad { i8*, i32 }
+          catch i8* null
+  ret void
+
+try.cont:
+  call void @llvm.memcpy.p0i8.p0i8.i64(i8* %dst, i8* %temp, i64 64, i32 8, i1 false)
+; CHECK: call void @llvm.memcpy.p0i8.p0i8.i64(i8* %dst, i8* %src, i64 64, i32 8, i1 false)
+  ret void
+}
+
+; Test that memcpyopt works across the unwind edge of an invoke.
+
+define hidden void @test_unwind(i8* noalias %dst, i8* %src) personality i8* bitcast (i32 (...)* @__gxx_personality_v0 to i8*) {
+entry:
+  %temp = alloca i8, i32 64
+  call void @llvm.memcpy.p0i8.p0i8.i64(i8* %temp, i8* nonnull %src, i64 64, i32 8, i1 false)
+; CHECK: call void @llvm.memcpy.p0i8.p0i8.i64(i8* %temp, i8* nonnull %src, i64 64, i32 8, i1 false)
+  invoke void @invoke_me()
+          to label %try.cont unwind label %lpad
+
+lpad:
+  landingpad { i8*, i32 }
+          catch i8* null
+  call void @llvm.memcpy.p0i8.p0i8.i64(i8* %dst, i8* %temp, i64 64, i32 8, i1 false)
+; CHECK: call void @llvm.memcpy.p0i8.p0i8.i64(i8* %dst, i8* %src, i64 64, i32 8, i1 false)
+  ret void
+
+try.cont:
+  ret void
+}
+
+declare void @llvm.memcpy.p0i8.p0i8.i64(i8* nocapture writeonly, i8* nocapture readonly, i64, i32, i1)
+declare i32 @__gxx_personality_v0(...)
+declare void @invoke_me() readnone

llvm/test/Transforms/MemCpyOpt/nonlocal-memcpy-memcpy.ll

@@ -0,0 +1,114 @@
+; RUN: opt < %s -memcpyopt -S | FileCheck %s
+; Make sure memcpy-memcpy dependence is optimized across
+; basic blocks (conditional branches and invokes).
+
+%struct.s = type { i32, i32 }
+
+@s_foo = private unnamed_addr constant %struct.s { i32 1, i32 2 }, align 4
+@s_baz = private unnamed_addr constant %struct.s { i32 1, i32 2 }, align 4
+@i = external constant i8*
+
+declare void @qux()
+declare void @llvm.memcpy.p0i8.p0i8.i64(i8* nocapture writeonly, i8* nocapture readonly, i64, i32, i1)
+declare void @__cxa_throw(i8*, i8*, i8*)
+declare i32 @__gxx_personality_v0(...)
+declare i8* @__cxa_begin_catch(i8*)
+
+; A simple partial redundancy. Test that the second memcpy is optimized
+; to copy directly from the original source rather than from the temporary.
+
+; CHECK-LABEL: @wobble
+define void @wobble(i8* noalias %dst, i8* %src, i1 %some_condition) {
+bb:
+  %temp = alloca i8, i32 64
+  call void @llvm.memcpy.p0i8.p0i8.i64(i8* %temp, i8* nonnull %src, i64 64, i32 8, i1 false)
+; CHECK: call void @llvm.memcpy.p0i8.p0i8.i64(i8* %temp, i8* nonnull %src, i64 64, i32 8, i1 false)
+  br i1 %some_condition, label %more, label %out
+
+out:
+  call void @qux()
+  unreachable
+
+more:
+  call void @llvm.memcpy.p0i8.p0i8.i64(i8* %dst, i8* %temp, i64 64, i32 8, i1 false)
+; CHECK: call void @llvm.memcpy.p0i8.p0i8.i64(i8* %dst, i8* %src, i64 64, i32 8, i1 false)
+  ret void
+}
+
+; A CFG triangle with a partial redundancy targeting an alloca. Test that the
+; memcpy inside the triangle is optimized to copy directly from the original
+; source rather than from the temporary.
+
+; CHECK-LABEL: @foo
+define i32 @foo(i1 %t3) {
+bb:
+  %s = alloca %struct.s, align 4
+  %t = alloca %struct.s, align 4
+  %s1 = bitcast %struct.s* %s to i8*
+  call void @llvm.memcpy.p0i8.p0i8.i64(i8* %s1, i8* bitcast (%struct.s* @s_foo to i8*), i64 8, i32 4, i1 false)
+; CHECK: call void @llvm.memcpy.p0i8.p0i8.i64(i8* %s1, i8* bitcast (%struct.s* @s_foo to i8*), i64 8, i32 4, i1 false)
+  br i1 %t3, label %bb4, label %bb7
+
+bb4:                                              ; preds = %bb
+  %t5 = bitcast %struct.s* %t to i8*
+  %s6 = bitcast %struct.s* %s to i8*
+  call void @llvm.memcpy.p0i8.p0i8.i64(i8* %t5, i8* %s6, i64 8, i32 4, i1 false)
+; CHECK: call void @llvm.memcpy.p0i8.p0i8.i64(i8* %t5, i8* bitcast (%struct.s* @s_foo to i8*), i64 8, i32 4, i1 false)
+  br label %bb7
+
+bb7:                                              ; preds = %bb4, %bb
+  %t8 = getelementptr %struct.s, %struct.s* %t, i32 0, i32 0
+  %t9 = load i32, i32* %t8, align 4
+  %t10 = getelementptr %struct.s, %struct.s* %t, i32 0, i32 1
+  %t11 = load i32, i32* %t10, align 4
+  %t12 = add i32 %t9, %t11
+  ret i32 %t12
+}
+
+; A CFG diamond with an invoke on one side, and a partially redundant memcpy
+; into an alloca on the other. Test that the memcpy inside the diamond is
+; optimized to copy ; directly from the original source rather than from the
+; temporary. This more complex test represents a relatively common usage
+; pattern.
+
+; CHECK-LABEL: @baz
+define i32 @baz(i1 %t5) personality i8* bitcast (i32 (...)* @__gxx_personality_v0 to i8*) {
+bb:
+  %s = alloca %struct.s, align 4
+  %t = alloca %struct.s, align 4
+  %s3 = bitcast %struct.s* %s to i8*
+  call void @llvm.memcpy.p0i8.p0i8.i64(i8* %s3, i8* bitcast (%struct.s* @s_baz to i8*), i64 8, i32 4, i1 false)
+; CHECK: call void @llvm.memcpy.p0i8.p0i8.i64(i8* %s3, i8* bitcast (%struct.s* @s_baz to i8*), i64 8, i32 4, i1 false)
+  br i1 %t5, label %bb6, label %bb22
+
+bb6:                                              ; preds = %bb
+  invoke void @__cxa_throw(i8* null, i8* bitcast (i8** @i to i8*), i8* null)
+          to label %bb25 unwind label %bb9
+
+bb9:                                              ; preds = %bb6
+  %t10 = landingpad { i8*, i32 }
+          catch i8* null
+  br label %bb13
+
+bb13:                                             ; preds = %bb9
+  %t15 = call i8* @__cxa_begin_catch(i8* null)
+  br label %bb23
+
+bb22:                                             ; preds = %bb
+  %t23 = bitcast %struct.s* %t to i8*
+  %s24 = bitcast %struct.s* %s to i8*
+  call void @llvm.memcpy.p0i8.p0i8.i64(i8* %t23, i8* %s24, i64 8, i32 4, i1 false)
+; CHECK: call void @llvm.memcpy.p0i8.p0i8.i64(i8* %t23, i8* bitcast (%struct.s* @s_baz to i8*), i64 8, i32 4, i1 false)
+  br label %bb23
+
+bb23:                                             ; preds = %bb22, %bb13
+  %t17 = getelementptr inbounds %struct.s, %struct.s* %t, i32 0, i32 0
+  %t18 = load i32, i32* %t17, align 4
+  %t19 = getelementptr inbounds %struct.s, %struct.s* %t, i32 0, i32 1
+  %t20 = load i32, i32* %t19, align 4
+  %t21 = add nsw i32 %t18, %t20
+  ret i32 %t21
+
+bb25:                                             ; preds = %bb6
+  unreachable
+}