[AliasAnalysis] Treat invariant.start as read-memory
Summary:
We teach alias analysis that invariant.start is readonly.
This helps with GVN and memcopy optimizations that currently treat.
invariant.start as a clobber.
We need to treat this as readonly, so that DSE does not incorrectly
remove stores prior to the invariant.start
Reviewers: sanjoy, reames, majnemer, dberlin
Subscribers: llvm-commits
Differential Revision: https://reviews.llvm.org/D23214
llvm-svn: 278138
diff --git a/llvm/test/Transforms/MemCpyOpt/invariant.start.ll b/llvm/test/Transforms/MemCpyOpt/invariant.start.ll
new file mode 100644
index 0000000..ed8d7ed
--- /dev/null
+++ b/llvm/test/Transforms/MemCpyOpt/invariant.start.ll
@@ -0,0 +1,49 @@
+; MemCpy optimizations should take place even in presence of invariant.start
+; RUN: opt < %s -basicaa -memcpyopt -dse -S | FileCheck %s
+
+target datalayout = "e-p:32:32:32-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:32:64-f32:32:32-f64:32:64-v64:64:64-v128:128:128-a0:0:64-f80:128:128"
+
+target triple = "i686-apple-darwin9"
+
+%0 = type { x86_fp80, x86_fp80 }
+declare void @llvm.memcpy.p0i8.p0i8.i32(i8* nocapture, i8* nocapture, i32, i32,
+i1) nounwind
+declare void @llvm.memcpy.p0i8.p0i8.i64(i8* nocapture, i8* nocapture readonly,
+i64, i32, i1)
+declare void @llvm.memset.p0i8.i64(i8* nocapture, i8, i64, i32, i1)
+
+declare {}* @llvm.invariant.start.p0i8(i64, i8* nocapture) nounwind readonly
+
+; FIXME: The invariant.start does not modify %P.
+; The intermediate alloca and one of the memcpy's should be eliminated, the
+; other should be transformed to a memmove.
+define void @test1(i8* %P, i8* %Q) nounwind {
+ %memtmp = alloca %0, align 16
+ %R = bitcast %0* %memtmp to i8*
+ call void @llvm.memcpy.p0i8.p0i8.i32(i8* %R, i8* %P, i32 32, i32 16, i1 false)
+ %i = call {}* @llvm.invariant.start.p0i8(i64 32, i8* %P)
+ call void @llvm.memcpy.p0i8.p0i8.i32(i8* %Q, i8* %R, i32 32, i32 16, i1 false)
+ ret void
+; CHECK-LABEL: @test1(
+; CHECK-NEXT: %memtmp = alloca %0, align 16
+; CHECK-NEXT: %R = bitcast %0* %memtmp to i8*
+; CHECK-NEXT: call void @llvm.memcpy.p0i8.p0i8.i32(i8* %R, i8* %P, i32 32, i32 16, i1 false)
+; CHECK-NEXT: %i = call {}* @llvm.invariant.start.p0i8(i64 32, i8* %P)
+; CHECK-NEXT: call void @llvm.memcpy.p0i8.p0i8.i32(i8* %Q, i8* %R, i32 32, i32 16, i1 false)
+; CHECK-NEXT: ret void
+}
+
+
+; The invariant.start intrinsic does not inhibit tranforming the memcpy to a
+; memset.
+define void @test2(i8* %dst1, i8* %dst2, i8 %c) {
+; CHECK-LABEL: define void @test2(
+; CHECK-NEXT: call void @llvm.memset.p0i8.i64(i8* %dst1, i8 %c, i64 128, i32 1, i1 false)
+; CHECK-NEXT: %i = call {}* @llvm.invariant.start.p0i8(i64 32, i8* %dst1)
+; CHECK-NEXT: call void @llvm.memset.p0i8.i64(i8* %dst2, i8 %c, i64 128, i32 8, i1 false)
+; CHECK-NEXT: ret void
+ call void @llvm.memset.p0i8.i64(i8* %dst1, i8 %c, i64 128, i32 1, i1 false)
+ %i = call {}* @llvm.invariant.start.p0i8(i64 32, i8* %dst1)
+ call void @llvm.memcpy.p0i8.p0i8.i64(i8* %dst2, i8* %dst1, i64 128, i32 8, i1 false)
+ ret void
+}